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blgiles78
06-06-2007, 12:15 PM
I have talked to several different people at indmar and at mastercraft and I am getting so much conflicting information. I am so frustrated! I have a 95 maristar with a 5.7 liter GM TBI injected engine. Indmar Marine's operators manual says the fuel pressure should be 30psi and Mastercraft's manual says 10 to 12 psi. I ordered a fuel pressure regulator from skidim using the engine serial number, and it runs at bout 12 psi. The boat runs better (except for an issue idling), but I am concerned about it running lean. So, I called Vince and he said 10 to 12psi seemed low. He sent me another regulator off of an engine he had at his place, and it has a pressure reading of 30 psi. THERE ARE TWO DIFFERENT REGULATORS! WHICH ONE IS RIGHT! Does anyone have the correct anwser? What is the fuel pressure suppose to be? This is a huge difference? :rant:

Sorry about the misspelling of aggravated !!!

trickskier
06-06-2007, 12:50 PM
Sorry, I can't help with your issue...............However, I would go with what ever Indmar recommends since it's their engine..............Good Luck!!!

ProTour X9
06-06-2007, 12:55 PM
I can't help you either.................but you spelled aggravated wrong

Storm861triple
06-06-2007, 01:23 PM
30 PSI is not right. The TBI style injectors will not fire reliably under that much pressure. Chevy TBI car's specs are 9-12 PSI, but there are SOME marine TBI engines that run as high as 18 PSI.

Does your regulator have an adjusting screw on the bottom of it? What color was your original spring? The new spring? Why did you change the regulator? It should be adjustable, and if so try adjusting it to compress the spring more and see how the engine likes it.

I used to have a "Crossfire Injected" Trans Am, which featured two 1 bbl TBI units on a cross ram intake. Different. Anyway, the car came w/a 170 hp 5.0L engine, and when I sold it it was running a 330 hp, 6.6L engine, under the original (albeit highly ported) intake and TBI's, w/the original ECM and chip w/stock programing. I made it work by changing injector sizes, timing, FP, and ultimately running a "marine" fuel pressure regulator which featured a vacuum reference port so it would run less FP at idle and more at WOT...like a multi port system. I guess my point is that you needn't be afraid of changing the FP adjustment on the regulator to "feed it what it wants".

74stars
06-06-2007, 02:05 PM
Is this the TBI (throttle body injection) or TPS (tuned port injection - like the vette/camaro/firebird) 30PSI seems way too high for a TBI set-up, but would be more in line with the TPS style injection. Also have you checked the spark plugs- If it is leaning out the electrodes will generally be dry and light tan in color. Too rich will usually be fuel fouled with black carbon present or with light black soot on them.

Storm861triple
06-06-2007, 02:23 PM
He said it was TBI in the first post:I have a 95 maristar with a 5.7 liter GM TBI injected engine.[/B]

And in the interest of accuracy, the Camaro's 'Vettes and 'Birds had TPI. You did have the "Tuned Port Injection" part right. ;)

Jesus_Freak
06-06-2007, 03:42 PM
30 PSI is not right. The TBI style injectors will not fire reliably under that much pressure. Chevy TBI car's specs are 9-12 PSI, but there are SOME marine TBI engines that run as high as 18 PSI.

Does your regulator have an adjusting screw on the bottom of it? What color was your original spring? The new spring? Why did you change the regulator? It should be adjustable, and if so try adjusting it to compress the spring more and see how the engine likes it.

I used to have a "Crossfire Injected" Trans Am, which featured two 1 bbl TBI units on a cross ram intake. Different. Anyway, the car came w/a 170 hp 5.0L engine, and when I sold it it was running a 330 hp, 6.6L engine, under the original (albeit highly ported) intake and TBI's, w/the original ECM and chip w/stock programing. I made it work by changing injector sizes, timing, FP, and ultimately running a "marine" fuel pressure regulator which featured a vacuum reference port so it would run less FP at idle and more at WOT...like a multi port system. I guess my point is that you needn't be afraid of changing the FP adjustment on the regulator to "feed it what it wants".

Please correct me here, but it seems the dramatic difference between these two scenarios is that the boat does not have an O2S; it has no way of knowing AFR. If this is true, the fuel pressure is not a degree of freedom.

WilliM1940
06-06-2007, 04:01 PM
My '95 Tahoe with 5.7 Litre TBI states dead head pressure at 13-15 psi. Even without the O2 sensor, the ECM is still using a table of values for valve opening, and more pressure is going to mean more fuel volume screwing up the stochiometric ratio.

WilliM1940
06-06-2007, 05:05 PM
Also, if you are having a problem idling, the idle mixture is controlled on my '95 Tahoe TBI by a stepper motor driven actuator with a pintel on the end, also driven by the ECM. Am assuming yours must be set up pretty much the same way. If idling was your problem all along, then you might want to check this out, there is a procedure for it.

WilliM1940
06-06-2007, 05:17 PM
Also, this engine liked to swallow throttle body to intake manifold gaskets, leaving you with a vacuum leak and high idle problem. Sorry about the multiple posts, I'm old and suffer from CRS.

Storm861triple
06-06-2007, 07:01 PM
Please correct me here, but it seems the dramatic difference between these two scenarios is that the boat does not have an O2S; it has no way of knowing AFR. If this is true, the fuel pressure is not a degree of freedom.
That is wrong. Whether you have an O2 or not, you can effectively change the A/F ratio w/the fuel pressure. On cars w/O2 sensors )before OBDII) the computer doesn't have much "adjustability"...even with the ability to read an O2. So adjusting the FP does affect the A/F ratio. On boat, it would be an even more effective way to A/F ratio adjustment.

Storm861triple
06-06-2007, 07:05 PM
Also, if you are having a problem idling, the idle mixture is controlled on my '95 Tahoe TBI by a stepper motor driven actuator with a pintel on the end, also driven by the ECM. Am assuming yours must be set up pretty much the same way. If idling was your problem all along, then you might want to check this out, there is a procedure for it.
That is not correct. The Idle Air Control motor has zero effect on the mixture AKA Air/Fuel ratio. All the IAC motor does is meter the air entering the engine at low speeds to control the idle speed. The ECM adjusts the A/F ratio based on manifold pressure, coolant temp, throttle position, and RPM (AKA "Speed Density").

Storm861triple
06-06-2007, 07:08 PM
My '95 Tahoe with 5.7 Litre TBI states dead head pressure at 13-15 psi. Even without the O2 sensor, the ECM is still using a table of values for valve opening, and more pressure is going to mean more fuel volume screwing up the stochiometric ratio.
Dead head is not how you measure fuel pressure in any engine. A dead head measurement will not be accurate, because you're eliminating the FPR from the system. If the fuel pump is operating properly, the FPR is the element that governs FP, therefore, needs to be included in a FP test. You need to "T" into the feed line before the FPR and hook a gauge to the "T". Then monitor FP w/the engine running and under a full load to ensure that the pump is maintaining pressure even during the engine's highest consumption.

JDK
06-06-2007, 07:13 PM
Indmar Marine's operators manual says the fuel pressure should be 30psi and Mastercraft's manual says 10 to 12 psi. I ordered a fuel pressure regulator from skidim using the engine serial number, and it runs at bout 12 psi. [/B]

Doesn't your fuel pump (mounted on the rear of the engine) have an internal bypass, meaning no regulator --- suction line and tank return on one end and high pressure line to tbi unit on the other end?
I have a Clymer manual and it also says 30 psi.for my 1995 350 tbi.
The reason I was interested in this is I was looking for a cheap fuel pump to keep as a spare, and I could find many 12 psi replacements for around $100. The only 30 psi replacements with the internal bypass were in the $300 range.
Anyone find the correct pump for cheap???

Storm861triple
06-06-2007, 07:15 PM
Also, this engine liked to swallow throttle body to intake manifold gaskets, leaving you with a vacuum leak and high idle problem. Sorry about the multiple posts, I'm old and suffer from CRS.
That one I agree w/completely. Certainly a vacuum leak will cause idle issues. What ARE the idle issues, BTW? The OP never stated.

What is CRS?

JimN
06-06-2007, 07:29 PM
If the motor has a fuel return line, the pressure should be around 30. If there's no return, it should be about 18. The injectors are fine with 30, since they're used in trucks and cars with larger TBI motors. Increasing the pressure and "giving it what it wants" isn't the best advice since higher pressure will feed it more, sometimes too much, gas considering the amount delivered is controlled by increasing the pulse width.

The plug tips would be tan in a car motor (wheat is the preferred color) and since these run richer than a car, they're usually a bit toward black. Too lean it going to be white and flaky.

JimN
06-06-2007, 07:34 PM
Storm- CRS is "Can't Remember Sh!t", which is better than having CRAFT syndrom, which is Can't Remember A Freakin' Thing.

Look at a Chrysler dealer for the pump, IIRC. Look for a part number on it and if it's generic Indmar/MC, call SkiDim or MC and say that you aren't near a MC dealer.

blgiles78
06-06-2007, 07:57 PM
Guys, I talked to Texas Mastercraft and they said that the fuel pressure on the boat with an engine mounted fuel pump should be about 10 to 12 psi, but if the fuel pump was located in the tank it would be around 30psi or higher. I also know that other engines use the same fuel pump set as mine, but they definitely run higher fuel pressures. Such as multiport engines LT1 for example. They also gave me a part number for fuel injectors from Oreilly Auto Parts. They said they would work fine. Are they correct about this? I feel my idling issue is related to a bad spray pattern from my injectors. The boat does seem to operate better with the 10 to 12 psi regulator in it. With the 30psi regulator in it there is a issue with the boat running rich and bogging.

Storm861triple
06-06-2007, 07:59 PM
If the motor has a fuel return line, the pressure should be around 30. If there's no return, it should be about 18. The injectors are fine with 30, since they're used in trucks and cars with larger TBI motors. Increasing the pressure and "giving it what it wants" isn't the best advice since higher pressure will feed it more, sometimes too much, gas considering the amount delivered is controlled by increasing the pulse width.
I stand corrected on the FP then. That's crazy b/c the Third gen guys w/TBI cars have had problems getting the injectors to perform that 30 PSI; it's too much for the Pintle weight on that larger TBI injector. Whatever though. If Indmar figured out how to make it work, good for them, I guess.

As for increased pressure feeding it "some times too much", that's when you'd LOWER the FP to "feed it what it wants". This level of "modding" is probably not appropriate here though.

Storm861triple
06-06-2007, 08:03 PM
They also gave me a part number for fuel injectors from Oreilly Auto Parts. They said they would work fine. Are they correct about this?
Once you know the pounds per hour rating of the injectors in your boat you can get injectors for any "GM TBI" from virtually any source. I bought mine for my Trans Am of "Dr. Injector" through ebay, for example.

I'm betting that they're around 90 pph, but you need to know that data to order some from someone other than a "boating source" that knows the part number/spec for that sized injector.

blgiles78
06-06-2007, 08:33 PM
Does anyone know what pph rate is in this Indmar application?

Storm861triple
06-06-2007, 09:51 PM
Blgiles78, I thought about it more, and if you post the Part number from your injectors, I can probably figure out how many PPH they are. Do you know how to remove them from the TBI unit? (It's about as easy as it looks).

Keep in mind that a vacuum leak is far more likely than a bad injector. These injectors rarely cause problems. You've verified a junky spray pattern visually?

blgiles78
06-06-2007, 11:18 PM
Yes, I have ran the injectors at 12 psi and 30 psi. The spray pattern is not good at either range. The spray should be a fine mist in a circular cone. Mine is not putting out a spray like this. It is in larger droplets in a poorly defined circle. It fact, gas seems to be building up on the injectors themselves and actually dripping off. I know that is it very odd for the injectors to go bad, I think that it is more likely that the previous owner had the wrong injectors installed. He told me when I bought the boat that he had a set of injectors put in it. I actually have the reciept for a marine dealer. I do not think that this shop was an Indmar or MC dealer. I am concerned that they installed the wrong parts. The injectors do not look like any I have seen in other applications. The nozzle on the injectors are recessed back up in the injector itself. They have a cone shaped funnuel that go back up to a circular grouping of oval shaped holes. Most injectors that I have seen are flat across the bottom with the nozzle in the center. Has anyone seen injectors like I have described? I am not basing any part numbers on the injectors in the boat due to the concerns I am having.

I really appericate all of the action on this post!:D

WilliM1940
06-07-2007, 12:18 AM
Storm:

"That is not correct. The Idle Air Control motor has zero effect on the mixture AKA Air/Fuel ratio. All the IAC motor does is meter the air entering the engine at low speeds to control the idle speed. The ECM adjusts the A/F ratio based on manifold pressure, coolant temp, throttle position, and RPM (AKA "Speed Density")."

I also stated the ECM controls the Idle air actuator, therefore the ECM controls the A/F ratio. Idle air is another tool of the ECM. If this thing doesn't work I guarantee your idle will be screwed up, his initial undefined problem.

"Dead head is not how you measure fuel pressure in any engine. A dead head measurement will not be accurate, because you're eliminating the FPR from the system. If the fuel pump is operating properly, the FPR is the element that governs FP, therefore, needs to be included in a FP test. You need to "T" into the feed line before the FPR and hook a gauge to the "T". Then monitor FP w/the engine running and under a full load to ensure that the pump is maintaining pressure even during the engine's highest consumption."

Right, but he was asking what regulator to use. The pump on the 5.7 TBI apparently does not put out over 30 psi, so the higher pressure regulator is not suitable. My Chevy manual states (assuming it is still a basic Chevy) regulated pump pressure is down to 9-12 psi. And there is a return line at this pressure.

If it is still a Chevy, then the Mastercraft ratings are correct.

Jesus_Freak
06-07-2007, 01:02 AM
That is wrong. Whether you have an O2 or not, you can effectively change the A/F ratio w/the fuel pressure. On cars w/O2 sensors )before OBDII) the computer doesn't have much "adjustability"...even with the ability to read an O2. So adjusting the FP does affect the A/F ratio. On boat, it would be an even more effective way to A/F ratio adjustment.

Yes, my friend, that is precisely my point: AFR is modified with fuel pressure on an open loop system (boat), while on a closed loop system, the injectors will back off as needed. There is plenty of adjustment with an O2S. The computer has the entire operational window (depending on the reciprocal of the engine speed) to modify the pulse width. The mass flow through the injectors, without any feedback loop, will be directly proportional to the square root of the differential pressure across the injectors. 30 PSIG versus 12 PSIG is about 60% more fuel (for a given pulse width, neglecting any additional frictional losses in the fuel rail, etc.).

I am not telling you anything you dont already know. In fact, I trust you know more than I do on this subject. Your point in your early post was that you did some impressive things with your car. I agree. I am jus sayin' that one has to be more careful adjusting things on a boat, or any open loop system (assuming this person cares about fuel consumption, valve life, exhaust temperatures, etc.)

WilliM1940
06-07-2007, 09:12 AM
This is a bit off the subject, but can anyone tell me why you all would want to screw with a computer based engine operating system in a boat when it is not required for emissions purposes? I mean, was that on somebody's wish list when they started chucking these things into boats, or is it because GM and Ford just delivered it that way? Rant over.

JimN
06-07-2007, 09:57 AM
If the injectors were changed with the wrong part, it was due to laziness, the right ones were out of stock, impatience or someone thought they knew how to modify it without benefit of proper test methods/equipment/clue. The part number is on the injector housing. How hard can it be to get the right ones?

"Trying out" different injectors and fuel pumps is hardly a scientific method for improving performance. Indmar and MC did a lot of testing to get the motors to do what they do, on real dynos, by people who know what they're doing. Fuel delivery is variable, contrary to the comments of some people and high demand calls for two things- higher fuel pressure and longer pulse width. Computers are really good at counting, which means that altering pulse width is a piece of cake. Injection replaced carbs because of all of the problems with reliability. Carbs are finickey, get clogged, floats go bad, there are too many ways to adjust them in a way that makes the motor all but useless and when the air temperature is high/boat is running hard, all kinds of problems happen. Injection is harder to diagnose for a lot of people due to its electronic nature but it is definitely more reliable. Carbs are a good, cheap way to get a motor to run but difficult to set accurate fuel/air ratios in a wide range of situations without changing parts.

There is usually a part number on most of the motor parts, including the fuel pump. Why not look at that or ask others to post the number on theirs, when they're from similar boats? The engine serial number can indicate if a list of motors are from the same year's production and unless one has a return line and another doesn't, the pumps should be the same.

WilliM- until recently, it wasn't required for emissions standards but it is now. CARB and the EPA have been getting very sticky about emissions in high population density areas and since these are not high production vehicles, it's not as cost-effective to make several versions of the same motor so they make them basically the same for all parts of the country.

WilliM1940
06-07-2007, 12:35 PM
Interesting, I guess it is only a matter of time before boats are completely regulated all over. Good quality subject matter.

JimN
06-07-2007, 01:20 PM
Regulated- you mean emissions, etc? The Coast Guard and EPA/CARB already do that. CARB makes it necessary for the boats to meet spec in a large place and that makes it easy to meet spec in the rest of the country, since California has more strict emissions standards than the rest of the states.

If the insurance industry had their way, they would regulate everything. We talked about this at MC training when the topic of 'throttle by wire' was brought up. The 'crashless vehicle' was mentioned and when you think about cars having throttle by wire, ABS brakes that are computer controlled, electric shifting and proximity sensors, adding GPS and a master controller doesn't seem that far off. Too fast- it slows the car down. Too close, it increases the distance. Going off-course, it steers it back on. Pretty soon, people will be able to read, do their makeup, sleep, talk on the phone and watch TV without having to worry about actually driving.

Jesus_Freak
06-07-2007, 01:38 PM
If the insurance industry had their way, they would regulate everything.

Does Burt know you are talking smack about him? :)

Pretty soon, people will be able to read, do their makeup, sleep, talk on the phone and watch TV without having to worry about actually driving.

Perfect Pass allows this now, right?:rolleyes:

Storm861triple
06-07-2007, 01:53 PM
I also stated the ECM controls the Idle air actuator, therefore the ECM controls the A/F ratio. Idle air is another tool of the ECM. If this thing doesn't work I guarantee your idle will be screwed up, his initial undefined problem.
Once again, that logic (the way you typed it anyway) is not correct since the IAC motor does not control or have any effect on the A/F ratio at all. Obviously the ECM controls the A/F ratio; that's why it exists. But it doesn't do it using the IAC. A broken IAC will do nothing other than cause the engine to idle at the wrong speed (depending on the position the IAC is in when it breaks), and not compenstate for gear shifting/load changes, etc. Since the OP never stated what the "idle issues" are, I'm not sure why we are talking about IAC's in the first place.

As I stated earlier, after 10+ years of modding a twin TBI equiped Trans Am, (in addition to being a mechanic at the same time) I'm pretty well versed in the functions of the ECM, IAC, and everything else under the hood of a Chevy.

The OP's description of the spray pattern pretty much sheds light on where his issues lie. Or at least one issue. Step one for the OP is to get the proper part number and get the proper injectors in there. Step two is to get the propper FP spec for his particular combo, and make that happen, whether it be by changing FPR springs, adjusting the spring height w/the current regulator or leaving it untouched if it's already correct.

JimN
06-07-2007, 02:04 PM
"Does Burt know you are talking smack about him?"

Burt who? (Sorry if I should know who Burt is, Burt)


"Perfect Pass allows this now, right?"

Yeah, but it can still crash. Wait till they get everything dialed in- hundreds of boats on every lake, going in perfect circles, in unison at a blazing 5 MPH.

Jesus_Freak
06-07-2007, 02:12 PM
"Does Burt know you are talking smack about him?"

Burt who? (Sorry if I should know who Burt is, Burt)


"Perfect Pass allows this now, right?"

Yeah, but it can still crash. Wait till they get everything dialed in- hundreds of boats on every lake, going in perfect circles, in unison at a blazing 5 MPH.

Sorry....Burt is Monte72 and is in the insurance business.

Yeah, I was just kidding about PP. It is far from "complete".

TMCNo1
06-07-2007, 02:15 PM
"Does Burt know you are talking smack about him?"

Burt who? (Sorry if I should know who Burt is, Burt)


"Perfect Pass allows this now, right?"

Yeah, but it can still crash. Wait till they get everything dialed in- hundreds of boats on every lake, going in perfect circles, in unison at a blazing 5 MPH.


Burt/Bert, is Monte72, who is in insurance.

WilliM1940
06-07-2007, 04:22 PM
Storm861:

Once again, that logic (the way you typed it anyway) is not correct since the IAC motor does not control or have any effect on the A/F ratio at all. Obviously the ECM controls the A/F ratio; that's why it exists. But it doesn't do it using the IAC. A broken IAC will do nothing other than cause the engine to idle at the wrong speed (depending on the position the IAC is in when it breaks), and not compenstate for gear shifting/load changes, etc. Since the OP never stated what the "idle issues" are, I'm not sure why we are talking about IAC's in the first place.

First off, lets be clear, the man has an idle issue, he did not specify, so I threw this out there for consideration. We can do that here. I don't even know if his Indmar Chevy TBI has an IAC motor.

Secondly, no, there will be no compensation most likely for load or gear changes with this actuator, the engine is idling, fuel introduction is most likely fixed (open loop). The throttle plate is closed. However, with fuel still being introduced to the engine for it to run at idle, it needs air in the proper proportion. This is the job of the IAC motor (if it exists), to meter the air at proper proportions at idle for the fuel charge. You will let me know I am sure, if I am wrong, or perhaps we have a semantics problem? Or is it air metered, and fuel introduced to proper ratio? How would that work open loop?

I do know that the IAC in a broken state probably introducing too much air on my car drove me down a level road at 45 mph. I am assuming fuel was added to keep the F/A ratio proper according to the O2 sensor. It didn't care where my foot was. Too much air, too much fuel but in the proper proportions. With an open loop system and no check on rich/lean, perhaps this would lead to stumble etc.

Anyway, I am using this as a learning experience. I am not going to tell you I am an expert, but a miffed consumer who really doesn't like to work on systems without the full disclosure of controlling software and the required tools to work with it. Most of the time bits and pieces in the manuals have to be connected together to get the whole picture.

And yes, it sounds like he already had a bit of a handle on the problem when he posted first.

blgiles78
06-07-2007, 09:46 PM
I sent an email to mastercraft using this website. I supplied them with a HIN number and engine serial number on my boat, and they sent me a reply today. They said they spoke to Indmar and the fuel pressure is suppose to be 10 to 12 psi.

JimN I know you said if it has a return fuel line the pressure should read about 30psi, but mine does have the return fuel line and MC say it should be running at the lower psi. I am thinking MC is correct due to the fact that the boat seems to run better at this fuel pressure.

I know you guys have been discussing the IAC. The boat does have one right on the throttle body next to the TPS sensor. The boat is not idling high. It is idling low, rough and dies every now and then. I do believe this is due to bad injector spray pattern. If this is the case and fuel pressure should be at 12psi, (the same as a Chevy Truck) will an automotive injector from a Chevy truck work in this application. I am concerned that the boat injectors are running a higher pph injector, but I do not know. Can injectors under a given fuel pressure be built to have different pph ratings?

Monte
06-07-2007, 10:41 PM
Burt/Bert, is Monte72, who is in insurance.

You rang?:D


This thread is far too technical for me to become involved in:(


Now I CAN tell you about auto, home, inland marine, farm, commercial, liability, life, health, long term care, med supp, and other such beasts8p ;)

Specs?? Got nothin.........

Storm861triple
06-07-2007, 10:41 PM
...The throttle plate is closed. However, with fuel still being introduced to the engine for it to run at idle, it needs air in the proper proportion. This is the job of the IAC motor (if it exists), to meter the air at proper proportions at idle for the fuel charge. You will let me know I am sure, if I am wrong, or perhaps we have a semantics problem? Or is it air metered, and fuel introduced to proper ratio? How would that work open loop?

I do know that the IAC in a broken state probably introducing too much air on my car drove me down a level road at 45 mph. I am assuming fuel was added to keep the F/A ratio proper according to the O2 sensor. It didn't care where my foot was. Too much air, too much fuel but in the proper proportions. With an open loop system and no check on rich/lean, perhaps this would lead to stumble etc.

Anyway, I am using this as a learning experience. I am not going to tell you I am an expert, but a miffed consumer who really doesn't like to work on systems without the full disclosure of controlling software and the required tools to work with it. Most of the time bits and pieces in the manuals have to be connected together to get the whole picture.

And yes, it sounds like he already had a bit of a handle on the problem when he posted first.
I will[ let you know why you are wrong. :)

The engine, whether it's in open loop or closed (open on a boat all the time), meters fuel in accordance w/information the ECM recieves from various SENSORS. The ECM interacts w/two things; sensors and actuators. The IAC is an actuator.

SO the ECM doesn't inject a "fixed" amount of fuel for idle, then control the mixture w/the IAC. That is not thinking is not correct. The ECM doesn nothing w/the IAC except meter air into the engine to govern engine speed at idle. That's IT.

THEN it adjusts fuel flow (open loop OR closed) based on input from the MAP sensor, Coolant sensor, Throttle positions sensor, and RPM. That is it. The ECM couldn't "care less" what the orientation of the IAC is; it will get readings from the other sensors that allow it to calculate the proper A/F ratio, and will do what it needs to w/ injector pulse width to make that happen. If the IAC is stuck wide open, the result will be a proper mixture, and a REALLY high idle, as you experienced w/your truck.

Now IF the programming is GOOD, it the above scenario will throw a check engine light, because the ECM should be programmed such that at IDLE (based on the TPS) it should see x RPM, x MAP, and instead it's seeing Y RPM and Y MAP readings...and those aren't right.

Is this clearing things up? The ECM doesn't meter air w/the IAC to control mixture.

All Chevy based engines w/TBI have an IAC, BTW. :)

blgiles78 symptoms (now that he's described them) are in line w/a leaking/screwed up injector.

JimN
06-07-2007, 10:47 PM
The IAC could potentially cause an idle problem if it was open less than what the program calls for. If it opens too far, the idle speed would increase and more fuel would be injected, to a point, because the ECM sees the MAP and TPS input. 2% or less throttle position is idle in the eyes of the ECM. Choking the idle air (IAC closing too much) affects the MAP reading and could cause stumbling, bad fuel cone and dying. Why not crack the throttle a touch at idle and see if the problem goes away? If the throttle plates are closed (actually not totally, or not much gas would get in, assuming a really good seal), the idle RPM being low will cause less vacuum at the top of the plates and proper atomization won't occur. Is there any chance of hooking it up to a diagnostic computer so the IAC can be functioned? There are IAC open/close buttons and manually setting the idle speed is done this way.

WilliM- The IAC causing high idle caused the MAP to tell the ECM to deliver more fuel and may have decided that the TPS had gone open or failed. If it was a one-time thing, a code may or may not have shown up but if the ECM looked at it as having failed, the usual default is to see the TPS as being at ~12% throttle and turns over control of engine run to the MAP sensor. That's not far from 45 MPH on flat road, either.

blgiles- interesting that MC says fuel pressure should be 10-12 pounds- we were told at CM training the same thing I posted and we were trained by the same people who did the calibrations for MC and IIRC, Indmar. I still think the best way to replace the injectors or verify that they are correct is to look at the part numbers on them. A call to MC would let you know what their replacement part number is and they can be compared.

I just looked at my notes from class and the injectors are the same as the 305 C.I.D. motor, not the small truck. Also, unless they changed the pressure after I was at training, we were definitely told that the older systems were at 18 pounds and the newer ones (by early '98) were at 30 pounds. The 1997 MC manual shows that "With the ignition "ON", engine "OFF", fuel pressure should be 186-228 kPa (27-33 psi)".

One thing I haven't seen is mention that codes were checked. That's one thing I would absolutely recommend doing ASAP. The light may not be on but there may be a 21, 22 (TPS) or 33, 34 (MAP). Again, the injector part numbers are in plain view, on the top of each one. That's one thing I would want to verify as being correct. The wrong injector for the pressure can cause this kind of issue. If the orifice is too large, it won't come out at the same speed and in the same pattern as the right one (think garden hose spray pattern).

JimN
06-07-2007, 11:16 PM
Storm- "The ECM doesn nothing w/the IAC except meter air into the engine to govern engine speed at idle. That's IT." is close but the IAC does follow the throttle position, in order to allow smooth transitions in acceleration/deceleration. Stumble at hard throttle down is usually caused by "IAC overshoot". The program tells the IAC to park at key OFF and to open a specific number of steps at key ON and at idle. In that you are correct- it's an actuator but does a little more than what you say.

The ECM has fuel tables and at set throttle positions, it may increase or decrease but the baro reading at every key ON cycle tells it if the fuel delivered needs to be normal or less for high altitude.

"The ECM doesn't meter air w/the IAC to control mixture."

Right- the IAC helps to stabilize idle quality and speed, hence, the name.

These motors, being open loop are well controlled. Not as tightly wrapped as a multi-port system but not exactly the SWAG method, either.

JimN
06-07-2007, 11:19 PM
Who wants a regional "Forensic Diagnostic Center" system for boat owners?:D

blgiles78
06-07-2007, 11:33 PM
JimN here is the email that MC sent me:

Hi Mr. Giles,

I have spoken to Indmar and they said your first regulator which had the psi between 10-12 is correct. I will not run lean at this psi. He said if you are experiencing idle problems then that will be due to another issue. He said that could be due to several things which he could not diagnose without actually looking at the engine so he suggests you have a certified technician inspect it.


Thank You,

MasterCraft Customer Care

I know that you do not agree with this info, but that is what they sent. I will put an email in to get the part number for the injectors and I will try to match them to mine. More info to come.

JimN
06-08-2007, 12:29 AM
It's not that I disagree with the info but that quote is directly from my manual and notes. Maybe they need to know that the available information has conflicts.

PendO
06-08-2007, 12:49 AM
JimN here is the email that MC sent me:

Hi Mr. Giles,

I have spoken to Indmar and they said your first regulator which had the psi between 10-12 is correct. I will not run lean at this psi. He said if you are experiencing idle problems then that will be due to another issue. He said that could be due to several things which he could not diagnose without actually looking at the engine so he suggests you have a certified technician inspect it.


Thank You,

MasterCraft Customer Care

I know that you do not agree with this info, but that is what they sent. I will put an email in to get the part number for the injectors and I will try to match them to mine. More info to come.

I'm confused ... JimN, you work for Indmar, right? ... and yes, I would like it if you opened up a regional diagnostic center:)

Storm861triple
06-08-2007, 01:48 AM
I know the IAC does more than what I said, but I was trying to keep it simple for the poster I was replying to, to show that it doesn't control or affect A/F ratio, which it doesn't.

A closed IAC could cause a very low idle, but the engine should still idle smoothly to the point that it's on the brink of stalling. If Indmar's programming is decent at all, the MAP value would be affected, but the programming would keep the A/F ratio correct and the idle would still be fine. I know this because I played w/this very thing on my aformentioned Trans Am, and could achieve a smooth idle down to 400 RPM even w/a 224/234 duration cam. If I could do that, I think we can assume that Indmar's programming should be able to as well. Even though MAP would rise w/lower RPM, RPM is declining too, and the programming should be there to accomodate that combination of RPM and MAP.

Laslty closed IAC and low idle speeds will have no affect on spay cone pattern. That is dictated by the injector design and FP which remains constant, regardless of engine RPM.

Anyway, the OP stated that he observed a poor spray pattern, and that can only be caused by three things;
1. VERY low FP
2. Faulty/clogged injector
3. Leaking injector O-rings

JimN
06-08-2007, 09:26 AM
Pendo- no, but I stayed at a....

PendO
06-08-2007, 09:33 AM
Pendo- no, but I stayed at a....

I was thinking enginenut (wasn't I) ... my bad ... but I'd still like the 1-800-call-jim phone number for emergency engine issues:)

JimN
06-08-2007, 09:40 AM
If the IAC was completely closed, it wouldn't run at all. The IAC is not open very far at idle and if it closes completely, tehre will be very little air getting in. As an example, when the 2000 LTR had a hot-start issue due to Rochester not continuing to supply the throttle plate with the 3/16" hole, the program was changed so the IAC idle position would go from 11 steps to about 17. Crack the throttle and they would start all day long but not if it was closed.

When you had yours running at 400RPM, were you able to move the IAC in discreet steps?

I was going to mention the O rings but forget when I posted last. Good point.

Either way, I think more testing needs to be done that hasn't been mentioned, like the line pressure, since that's ahead of the regulator, anyway and that's where the 18-30 psi should be found, depending on the year of the motor. I'm not sure '95 motors have the Shrader valve- I think not.

JimN
06-08-2007, 09:41 AM
"but I'd still like the 1-800-call-jim phone number for emergency engine issues"

Or auto conference call to MC and Indmar.

PendO
06-08-2007, 09:49 AM
"but I'd still like the 1-800-call-jim phone number for emergency engine issues"

Or auto conference call to MC and Indmar.

Like On-Star for your boat ... funny thing is I had the service brake system lihgt come on our chevy the other evening driving back from seattle, I push the on-star button and the gal runs the engine diagnostics and tells me it is an issue with the ABS system, "if you feel comfortable you can drive it home, or we can send a tow truck ..." I let her know I was 200 miles from home and would rather just drive it home and get it checked in the morning, but I was glad that I could have push-button diagnostics ... the light stayed on for 200 miles, but when I woke up the next morning he "code" was gone ... not sure how I feel about that, but an on-star system with engine diagnostics would be pretty dam cool, or even a way for a consumer to just plug in a cell phone so that codes could be read while you were actually having the problem ... cost prohibitive, but a guy can dream:)

JimN
06-08-2007, 09:53 AM
The cell phone connection is something Volvo-Penta was doing with their systems being installed in big boats, like over 32'. I don't know if they still do it but they called it "The Presidential" package. It was so customers could call in, V-P would run diagnostics and at least get the boat to limp in. More for off-shore boaters, though.

Storm861triple
06-08-2007, 10:29 AM
If the IAC was completely closed, it wouldn't run at all. The IAC is not open very far at idle and if it closes completely, tehre will be very little air getting in. As an example, when the 2000 LTR had a hot-start issue due to Rochester not continuing to supply the throttle plate with the 3/16" hole, the program was changed so the IAC idle position would go from 11 steps to about 17. Crack the throttle and they would start all day long but not if it was closed.

When you had yours running at 400RPM, were you able to move the IAC in discreet steps?
This may be getting off topic a bit, but I think whether the engine runs or not w/the IAC closed depends on the minimum air setting spec. I would ASSUME (and that gets me into trouble, I know) that the min-air spec would be the same on TBI boats as on TBI cars, BUT since Indmar doesn it's own programming, maybe not. Anyway, the cars will run fuun (albeit very low RPM) w/the IAC closed as shown below...

I didn't have control of discreet steps, but I was able to close the IAC all the way. On the car, that is how you set the proper minimum air setting (throttle opening); close the IAC all the way (you could plug the IAC air inlet too), then set the throttle stops to achieve a 400 RPM idle speed. Then readjust the TPS and reactivate the IAC.

I also agree that further testing/checking needs to be performed. I still think the first thing that needs to happen is determining what injectors are in there, O-ring condition, and injector condition. Once all that is sorted out, if a problem still exists then a FP test again. You should be able to test anywhere between the fuel pump and the TB to get a proper reading.

blgiles78
06-08-2007, 10:31 AM
JimN the differences in specs is what my orginial complaint was. No one seems to be 100% about the fuel pressure specs. I did take the FP in the steel line before the regulator. My regulator is on the throttle body and it is the last thing the fuel runs into before existing the throttle body. I installed a Shrader Valve in the steel line just after the fuel filter. This is where I got my pressure readings. The spray pattern is bad at 30psi and 12psi. So the pressure does not seem to be the cause. If I had leaking O rings wouldn't they leak when the fuel pressure comes up just before starting the engine? I do not see any leaking fuel at this time.

The one thing I have not had done is a code check, due to the fact that I do not have the equipment and the nearest dealer / tech is two hours away.

Storm861triple
06-08-2007, 11:56 AM
If I had leaking O rings wouldn't they leak when the fuel pressure comes up just before starting the engine? I do not see any leaking fuel at this time.
That is correct. If you do nto see leaking fuel when you have fuel pressure (Key on engine off), then you're O-rings are doing their job. Your fuel pressure test/location is good.

We need to get this injector ID issue sorted out.

JimN
06-08-2007, 12:34 PM
I agree that the injector issue, whatever it is, needs to be identified. If the pattern is bad at high and low pressure, something it up and I think it's the injectors, possibly being the wrong part.

A code reader isn't necessary, codes can be found with a paperclip and a test light. Test light is only needed if the check engine light doesn't work.

Paperclip in pins A and B of the data link connector will make the light flash 12, three times, then whatever codes are present will flash three times until the last code has been indicated and then it flashes 12 three times again to indicate the end of the sequence. Pins E and F connect to the test light and that's what is used to see the codes. The motor doesn't need to run for this test.

blgiles78
06-08-2007, 01:22 PM
Talked to MC again. Here is the reply they sent:

Hi Mr. Giles,

The correct injector # is 81556226, you need 2. We do not have a AC Delco cross reference, this is per Indmar the engine manufacturer. You can call Rambo Marine at (256) 828-3590 to order and have drop shipped to you.

Thank You,

Kim Mitchell
Warranty/ Tech Service

I am going to call these people to price out the injectors.

blgiles78
06-08-2007, 03:02 PM
I have done a bit more research. I called the people at Rambo Marine and the guy pulled the part. He said it was in an AC Delco box and gave me the AC Delco part number 217-2282. This part number matches the GM 7.4l injector. I think I am finally onto some good info. JimN isn't this what you said they should be.

Storm861triple
06-13-2007, 10:16 PM
That's good info. Hold please and I'll get the spec for you in lb/hr.

Good info that they aren't supposed ot be 5.0L injectors too! I thought that seemed amiss, because it generally takes .5 lb/hr to make a hp. So a 310 hp engine needs two ~90 lb/hr injectors -exactly what's in the 454 TBI Chevy's. The 5.0L TBI uses only 55 lb/hr injectors, for 110 lbs total, and a max of 220 hp. The engines are rated at 170 hp which puts it at the "safe" range of 80% of the injectors capacity.

JimN
06-14-2007, 12:14 AM
My notes said they use the 5.0L injectors but I don't have the part number. They may have changed to the 7.4L injectors when they increased the pressure and decreased the pulse width to whatever the motor needed to not run rich.

Will F- anything you can add to this?

blgiles78
06-14-2007, 07:01 PM
Guys, I got the new injectors in the mail today! They are definitely different from what is in the boat right now. I will install them tomarrow and let all of you know what happens.

blgiles78
06-15-2007, 12:26 PM
I am sick to the stomach. I put the injectors in today and it seems to have made the problem worse. The boat will crank and run great for about 15 seconds. Then it dies. The fuel pump is running and there is pressure in the system. I guess these may be the wrong injectors.

I am at the end of my rope and ready to give up!

JimN
06-15-2007, 12:34 PM
Are you leaving the fuel pressure gauge on the line when you run it? Watch for extreme drops when the RPM is increased.

Did you take a fuel sample? I don't remember. The pressure gauge may have a bleeder valve and a skinny tube on it- bleed some gas into a clean bottle and see if it's contaminated.

breezy
06-15-2007, 01:06 PM
BlGiles, are you sure that you have enough pressure?

blgiles78
06-15-2007, 03:00 PM
I did have a pressure guage on it and the pressure held strong at about 12psi. I have taken a fuel sample and the fuel is new and good. Even after the engine dies the pump will continue to run for about one or two seconds.

I am basing the pressure setting by the spec that MC told me to run. They said 12psi. I know a lot of people on here say 30psi. I have not tried 30psi. I am about ready to take in into a good shop. Does anyone around my area know a really good MC or Indmar shop? I live in south Mississippi.

WilliM1940
06-15-2007, 04:42 PM
Have you recorded the error codes yet as JimN suggested?

blgiles78
06-15-2007, 07:12 PM
No, I do not have the equipment. I am going to have it done soon. I sent the injectors back for credit. The boat is running much better with the old injectors in it and the new fuel pressure regualtor running 12 to 13psi.

Now, the only issue I seem to be having is a stalling issue while idling and a bit of a rough idle. The boat often has times where it does not want to start once it has warmed up. I believe these issues are related to the bad spray pattern on these injectors. I am not for sure though. I believe it is time to take the boat into a dealer. They can read the codes and get more info than I can. The other advantage of taking it in would be that if they put parts on that are wrong or do not help, it is their problem to find the right ones.

blgiles78
06-16-2007, 10:20 AM
Now I am about to pull my hair out. I got this email straight from Indmar Marine. Here it is:

We buy our fuel injectors from General Motors Service Parts. The P/N that we but them under is 19110534. 94 and 95 TBI engines use the low pressure regulator in the throttle body that regulates the pressure to 11-13 psi. Later models use a higher pressure system that regulates the pressure to 28-33 psi. I am pretty sure the same injectors are used for both systems. The ecm calibration compensated for the high or low pressure systems by modifying the fuel injector on time. We currently use the same fuel pump for both the higher and lower pressure fuel systems as the fuel pressure regulator in the throttle body controls the fuel pressure to the appropriate level. Hope this helps.

Larry Engelbert

Indmar Marine Engines

So the issue now is that the part number he gave me is the same part number on the injectors that I put in my boat. The boat would not run with these injectors. The boat would crank and run for about 15 seconds and then die. I am clueless here! How will the boat run with the injectors that are in it now, but it will not run with the ones that Indmar says should be in it!!!!

blgiles78
06-16-2007, 10:20 AM
Now I am about to pull my hair out. I got this email straight from Indmar Marine. Here it is:

(I pulled this info off the page due to respect for the techs at Indmar. They are working with me to solve my problem. Thanks for the good customer support!)

So the issue now is that the part number he gave me is the same part number on the injectors that I put in my boat. The boat would not run with these injectors. The boat would crank and run for about 15 seconds and then die. I am clueless here! How will the boat run with the injectors that are in it now, but it will not run with the ones that Indmar says should be in it!!!!

WilliM1940
06-16-2007, 09:59 PM
You have to pull the codes. Using the jumper and test lite as JimN suggested is not that difficult. There are other reasons other than injectors as to why that thing won't run, and with the codes it may lead you to the solution. Unfortunately, you have OBD1 like my truck, and when the obvious isn't a solution, it gets more difficult, even with the codes, as you may need to see the waveforms of the sensors and monitor the actuators, requiring increased gear. But pulling the codes you may find something obvious. My 95 Tahoe would not start because of the EGR valve being faulty. The code signalled EGR fault. That was a simple one, and saved me money. Look for a paper clip. Buy a test lite at the hardware store, or you are stuck with pulling out your wallet and taking it to a tech. You may have to anyway.

JimN
06-16-2007, 10:35 PM
OBD I, having less sensors is pretty easy, if someone knows what to look for.

If the codes are checked and any show up, I can provide the proper voltage ranges for the sensors.

bgiles- go to WOT (Wide Open Throttle) and try to start the motor. If it starts, shut it off immediately and adjust the TPS so it reaches it's maximum position at the same point as the throttle plate. Try to start it again. If it starts at WOT, there's a problem with the TPS, the harness or the ECM. It should not start with the throttle at WOT- that's how a flooded motor is cleared, since the ECM isn't supposed to fire the injectors at 100% throttle. Also, crack the throttle and see if it wants to idle better. If it does, verify that the TPS is the correct one for your motor (same as the trucks and cars). An LT-1 TPS will not work on your motor and the TBI TPS will not work on an LT-1 and I'm wondering if yours is faulty or the wrong part. Yours is acting like the throttle is closing rapidly and if there's a drastic enough change in position toward 0% throttle, the ECM takes it as hard deceleration and shuts the injectors off. A glitchy TPS can cause the same kind of thing.

If I remember, you bought this boat recently, right? I would be in the dealer's face about this.