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View Full Version : Fuel injected motor acting like a carbed


tdjaster
06-05-2012, 03:12 PM
My boat: '98 SportStar, 360-ish hours, very good condition.

My motor: 5.0L TBI Indmar (factory motor)

My problem: The boat is throttle-body fuel injected but it acts like my old '89 carbed ProStar. I have to give it gas and warm it up when I first put it in. I end up starting it with the throttle engaged (fast idle) most of the day. It'll rarely starts with just a turn of the key and no throttle. Overall, it seems like it doesn't feel good when it's in low RPMs.

My question: Is this normal of a TBI engine? Is there a simple fix?

Thanks!

André
06-05-2012, 04:50 PM
Could be many things.Does it run good when warm and pulling skiers?
Had the same problem on my 94 tbi 5.7,turn out to be a bad ECT sensor that was telling the ECM that the engine was hot when it was cold and wasn't injecting enough gas to start.
Also,a bad IAC,idle air control,could cause hard start.
Is your flame arrestor clean?
Hopefully others with more knowledge will chimes in...
Good luck!

ahhudgins
06-05-2012, 05:21 PM
My boat: '98 SportStar, 360-ish hours, very good condition.

My motor: 5.0L TBI Indmar (factory motor)

My problem: The boat is throttle-body fuel injected but it acts like my old '89 carbed ProStar. I have to give it gas and warm it up when I first put it in. I end up starting it with the throttle engaged (fast idle) most of the day. It'll rarely starts with just a turn of the key and no throttle. Overall, it seems like it doesn't feel good when it's in low RPMs.

My question: Is this normal of a TBI engine? Is there a simple fix?

Thanks!

That is not normal. Could be your IAC (called Idle Air Control, or Idle Air Solenoid) mounted on the TB. I don't have a picture handy. Manufacturers tell you not to clean them, but I have removed them and cleaned them out with throttle body cleaner. That would be the first thing I would check.

As Andre asked, does it run smooth above idle???

tdjaster
06-05-2012, 09:48 PM
That is not normal. Could be your IAC (called Idle Air Control, or Idle Air Solenoid) mounted on the TB. I don't have a picture handy. Manufacturers tell you not to clean them, but I have removed them and cleaned them out with throttle body cleaner. That would be the first thing I would check.

As Andre asked, does it run smooth above idle???


Runs great at speeds above idle. I'm pretty handy and do most of my own service but know nothing about ECTs, IACs, or cleaning any of them.

I'm not at all afraid to do the work, just need to know what to do. Can you provide any more info?

Thanks!

blackcreek
06-05-2012, 10:55 PM
Coolant temp sensor, check for proper ohms
IAC valve, clean it or change it
Clogged fuel injector, weak fuel pressure.
Weak ignition, plug wires or plugs
Check the base ignition timing

A timing light is your friend, use it to check the timing(you will probably need a way to bypass the computer timing so check the service manual).
With the engine running check each plug and wire with the timing light by clamping each wire and watching the strobe for drop outs.
Take the flame arrestor off and rev the motor watching the injector spray pattern. In the dark you can hook up the timing light to any plug wire and then point it at each injector and you will be able to see the spray pattern. You want a nice round cone looking spray with no dribbles and both sides looking the same.
http://www.witchhunter.com/images/tbi%20spray1.jpg

JimN
06-05-2012, 11:21 PM
My boat: '98 SportStar, 360-ish hours, very good condition.

My motor: 5.0L TBI Indmar (factory motor)

My problem: The boat is throttle-body fuel injected but it acts like my old '89 carbed ProStar. I have to give it gas and warm it up when I first put it in. I end up starting it with the throttle engaged (fast idle) most of the day. It'll rarely starts with just a turn of the key and no throttle. Overall, it seems like it doesn't feel good when it's in low RPMs.

My question: Is this normal of a TBI engine? Is there a simple fix?

Thanks!

This should idle like glass. How old is the impeller? If it isn't supplying enough raw water, the engine will run hot, making the ECM reduce fuel delivery.

Verify timing- you need to put it into diagnostic mode for this and some scan tools will do it as soon as you plug it in. If you just connect a timing light, you'll see the timing mark jumping all over and you can't set or verify timing that way. In diagnostic mode, the ECM defeats "spark stabilization" and the mark will be fixed at whatever position the timing is set to. You need to set it to 10°BTDC.

Check for codes, too. If you see 14 or 15, it's the coolant temperature sensor (ECT) and its resistance could very well be too low. This will cause the problem you described. Do you smell gas in the exhaust when it's running? That would mean the ECT's resistance is too high, making the ECM deliver too much fuel because it thinks the engine temperature is extremely low.

How old are the cap, rotor, plugs and wires? If you don't know or they're more than about 3 years old, replace them. The plugs should be AC with MR43T or TS- these have a stainless body and are marine plugs. The cap and rotor are standard GM replacement parts. I have a 5.7L in my Silverado and I use Borg Warner Gold Series parts. They have lifetime warranty and I got mine at O'Reilley's. The wires were originally Taylor and these are very good, although any good plug wires will work. Check the spark intensity, too. DON"T PULL A PLUG WIRE OFF OF THE SPARK PLUG WHILE IT"S RUNNING! 50K+ Volts isn't gonna make your day any better than it was.

tdjaster
06-06-2012, 07:36 AM
A bit more info based on your posts...

Impeller, plugs, and fuel filter were all newly replaced at the beginning of the season. Nothing more than 20 hours on it. Don't know about the cap, rotor, or wires because we bought the boat in March.

I've never used a timing light before, you may have to dumb down the instruction to get me started. When I said I do most of my own service, I should have clarified that that has been fluids, plugs, filters, packing, audio, battery, cap and rotor on my old boat, etc. Nothing too engine or ignition specific.

Again, thanks for all the info so far!

bturner2
06-06-2012, 08:09 AM
So the next question would be how did it run before you put these items in? Did the problem start right after you changed them? If the problem started immediately after you changed these items there's chance you induced the problem. If not it sounds like you have a ton of places to look with the recommendations made so far.

I had a similar problem on my 1995 200 MariStar which in my case was a fuel pump going bad.

JimN
06-06-2012, 08:15 AM
A bit more info based on your posts...

Impeller, plugs, and fuel filter were all newly replaced at the beginning of the season. Nothing more than 20 hours on it. Don't know about the cap, rotor, or wires because we bought the boat in March.

I've never used a timing light before, you may have to dumb down the instruction to get me started. When I said I do most of my own service, I should have clarified that that has been fluids, plugs, filters, packing, audio, battery, cap and rotor on my old boat, etc. Nothing too engine or ignition specific.

Again, thanks for all the info so far!

If you can install a stereo, you can use a timing light. You clip the pickup on the #1 plug wire and then the red and black on the battery or some other power source (like the battery cable at the starter and ground it on the block, if the battery is too far for the cables to reach). In the case of the pre-2005 engines, you can put the ECM in diagnostic mode by using a scanner/scan tool, as I posted, or you can bend a paper clip in half and insert the ends in terminals A and B of the ALDL (also called DLC, or diagnostic port- it's at the back of the engine) before starting the engine. When you do this, you'll have to manually bring the engine up to 1000 RPM before checking the timing. Loosen the distributor hold-down bolt and rotate the the distributor if the timing mark isn't at 10°BTDC.

When the paper clip is inserted in the diagnostic port, turn the key to ON and watch the check engine light- it will flash once, pause, flash twice a total of three times at the beginning of the sequence and at the end. These flashes denote 12. You'll need to watch from the beginning because the other codes will tell you if you have a bad sensor or if the ECM is seeing a bad value at a sensor input. I have asked for a sticky to be made of the code list- look in the Maintenance or electrical section for that, or google 'GM Engine Diagnostic Codes' to find a list if it's not here. Once any codes have been revealed, it will flash 12 three times.If it ONLY flashes 12, you have no stored codes.

tdjaster
06-06-2012, 08:31 AM
So the next question would be how did it run before you put these items in? Did the problem start right after you changed them? If the problem started immediately after you changed these items there's chance you induced the problem. If not it sounds like you have a ton of places to look with the recommendations made so far.

I had a similar problem on my 1995 200 MariStar which in my case was a fuel pump going bad.

Previous owner put in the impeller just before I purchased it. It has run this way since I got it...before and after my tune ups.

JimN
06-06-2012, 08:38 AM
Previous owner put in the impeller just before I purchased it. It has run this way since I got it...before and after my tune ups.

I would check it, anyway. They may have put this one in, but it could have been a spare from a previous year. It's still a "replaced impeller", right?

tdjaster
06-06-2012, 12:40 PM
I would check it, anyway. They may have put this one in, but it could have been a spare from a previous year. It's still a "replaced impeller", right?

I know it was a new one. He gave me the old one in the new one's box as a "just in case."

tdjaster
06-28-2012, 01:09 PM
Replaced the IAC and we're running perfect! Bought it for $70 at Advance Auto, replaced it myself in about 10 minutes. Awesome.

Thanks for everyone's wisdom!