View Full Version : Loss of Power

07-16-2008, 08:18 PM
When I got my boat out of storage this year at Action Water Sports in Grand Rapids, MI it had no top end power. It seems to run smoothly up to 15 MPH and then sounds like it is flooding, loses all power, and starts chugging along until I throttle back to idle for a minute and then it will go again up and repeat the above symtoms. I replaced both fuel filter, checked the air filter, and made sure that the knock sensor wires had not come loose. Any other suggestions?

07-18-2008, 07:19 AM
We need more info on your boat. What year? What engine?

Also - do a search, there are TONS of threads on this topic.

07-18-2008, 02:38 PM
It is a 1998 with the Corvette LT1 engine.

07-18-2008, 02:40 PM
It is a 1998 Maristar 225 with the Corvette LT1 engine.

07-18-2008, 03:44 PM
The screen in the fuel pump should be cleaned and I think this is what's causing the issue. The fuel pressure should be checked, too. If you have a fuel pressure gauge, preferably with the bleeder valve, take a fuel sample and put it in a clean, clear container. Let it sit for a half hour, or so, and look for not only particulates but also a milky cloud or water droplets.

It's still smooth at idle and up to the point of the power loss, right?

07-28-2008, 08:18 AM
I finally got some time over the weekend to pull the fuel pump and check the screen. It was clean and the fuel was clean. Unfortunately, I do not have a fuel pressure gauge yet so I could not check the actual pressure. When I do get one, what is the upper and lower limits on the fuel pressure that I should be looking for? I also changed the spark plugs since they had never been changed. Not so much from the symptoms of this problem but so that I could check to see if maybe one cylinder was fouling. Everything looked good there. I took the boat out afterwards and still get the same symptom. It starts easily, idles smoothly, good out of the hole acceleration, and good performance up to half throttle. As soon as it hits that point, the more throttle you give it the worse it runs. Not like it is missing but more like it is flooding. At full throttle, the boat is barely moving. Throttle back to idle, wait a few minutes, and then you can go again. If you have any more thoughts or ways to diagnois the problem, I would appreciate your input.

07-28-2008, 08:47 AM
Your plugs were never changed? They were about 8 years overdue.

The pressure should be about 30 lb and it shouldn't vary more than about a pound.

Put a can of Sea Foam in the tank, start it and don't run it at high RPM until it has run for at least 15 minutes. How old is the PCV valve?

I would also look at the fuel pickup tube screen. It's part of the aluminum piece the anti-siphon valve screws into, on top of the tank. I have seen all kinds of stuff clogging those and this sounds similar to what happened in those cases.

Has Action done the service on the boat in the past?

07-28-2008, 02:53 PM
a new set of plugs will go a long way to helping you boat run better !!

07-28-2008, 03:22 PM
I just pulled the pickup and fuel sensing unit off of the top of the tank and then took the plastic housing off. The intake screen was clean and there were only a few little particles in the plastic housing. I wiped them out and blew everything out with air to make sure it was clean and dry. Reassembled and took the boat out for a test. No change. It gets up to about 15 mph or half throttle and starts to lug down. The more throttle you give it the more it lugs down. It full throttle, the boat is hardly moving. With the pickup unit out of the tank, I was able to check the gas in the tank... it was clear with no water bubbles floating around the bottom and did not seem to have any noticeable particulate in it. Action has always done all of all of my maintenance and stores the boat for me every year... about $2K per year for winterizing, storage, and the things that they find wrong. The problem is each year when I get it back a new problem has cropped up. It was not doing this last year before I took it in for winterizing. As far as the PCV Valve, I do not know when it was last change. I will check it if you can tell me where it is at on this engine... a 97 LT1 I believe.

07-28-2008, 04:15 PM
I had very similar symptoms with mine last year. I have a 2000 PS205 w/310 hp and it may not apply to your LT1 but the problem was the MAP sensor which adjusts for variances in altitude. The sensor had failed and it would not accelerate beyond 20 to 25 mph.

07-28-2008, 07:35 PM
The fuel pressure needs to be checked before anything else. Until that's known, I wouldn't bother with anything else. You know it has spark, you know it has air. The only other things needed to make it run are compression and fuel.

07-29-2008, 09:11 AM
Can anyone tell me where the MAP sensor is on an LT1? It may be something as simple as being unplugged.

07-29-2008, 09:32 AM
It could be unplugged but it should also cause the MIL to light up.

Remove the black plastic covers and look for a black rectangular sensor with a three wire plug. The wire colors are black, blue and gray. It should be behind the throttle body, on the left side of the motor, if you look at the front of the motor.

07-29-2008, 11:07 AM
Jim... I bought an inexpensive ($40) fuel pressure gauge last night and just checked the fuel pressure. My gauge showed the pressure at 39 lbs at idle going up to 40 or 41 at 5K RPMs. I had been taking the boat out on the lake to test it but this morning I just left it in the slip and reved the engine. I did not push it past 5K but after about 10 seconds at 5K, the engine started lugging down and the RPMs started dropping. The more throttle I gave it, the lower the RPMs would go and at full throttle was less than 3K. I was monitoring the fuel pressure during all of this and it remained rock solid at 40 lbs, even while the engine was running poorly. I also checked several of the connectors by unplugging and re-plugging them just to make sure that I did not have a bad connection somewhere, but no joy. Any other thoughts? One person responded with the MAP sensor. Have you ever heard of that causing a similar problem? One point that I did forget to mention is that last year Action replace the EMC module ($1K). I don't know if it was new or reconditioned. Could that be causing the problem?

07-29-2008, 11:52 AM
If the pressure is stable, how stable is the idle speed? Does it surge at all, or surge and remain higher than 600RPM? If it does, look at the MAP sensor plug and remove the sensor. The port where it attaches to the intake needs a good seal and if it leaks, the vacuum reading won't be correct. A vacuum leak can cause performance to suffer. Also, if you have a multi-meter, probe the TPS plug's grey wire and make sure the voltage doesn't fluctuate when the throttle is in one position. This can be done with the motor OFF, key ON.

Don't pierce the wire's insulation. Insert a stick pin between the green silicon rubber seal and the wire. If you don't see voltage, keep probint until you do. Smoothly advnace the throttle through the whole range and if you see major dips in the voltage, it may be a bad TPS.

You need the Corvette TPS- the regular car/truck part won't work on your motor.

07-29-2008, 01:59 PM
Jim, I started the boat and let it idle for 5 minutes. RPMs on the tach was around 650 and did not vary or surge at all. I also tried a minute at 1K, 2K, 3K, and 4K with no variance or surges. I did locate a black rectanular sensor on the port side of the engine on top and just in front of the throttle body and it appears to have 3 wires but they are- black, light green, and grey. Slightly behind that and just in front of the air filter, is a more rounded sensor with 3 wires - black, blue, and grey. Just behind and slightly lower is another connector with 4 wires - green with black stripe, light green, blue, and light blue with with stripe. If the rectangular block is the MAP sensor, then I assume that the rounded sensor in front of the air cleaner is the Throttle Position Sensor? That is the one with the black, blue, and grey wires. I check the grey wire with the key on, and did not show any voltage at all regardless of the throttle position.

07-29-2008, 06:01 PM
The more rounded sensor is the TPS and the four wire part is the Idle Air Control (IAC) motor.

With the key OFF, remove the plug from the MAP sensor. Turn the key ON and measure DC volts on the blue wire. It should be in the 4+ VDC range. If you still don't have any voltage, it needs to be repaired but crimp connectors isn't the right way and won't last long- any repairs need to use the correct terminal and be crimped, soldered and sealed.

If you know someone who works on GM cars, they will know what to do. This is the same motor used in Corvettes and other cars, so it's not a proprietary design.

07-30-2008, 08:05 AM
Jim... there is a little difference in my setup than you are describing. On the plug going into the map sensor, I have three wires - from right to left as it plugs into the MAP they are: black, light green, and grey. With the switch off, I unplugged the connector and then with the key on, I measured the voltage at all three wires. black = 0; light green = 0; grey = 5.05. All measured with a DVM. I then shut off key, replugged MAP and unplugged TPS connector. On that I have three wires in a triangle configuration: Black, Blue, and grey. After turning on the key: Black - 0 Blue = 0; grey = 5.05. Turned key off, replugged TPS. I assume that the grey wires on both sensors is the input voltage. What wire on each sensor would I measure the output voltage?
Also, if you think that there is a high likelyhood of MAP or TSP, I am willing to replace them. Can I buy them at a standard auto store or do I need to go through Action because it is a marine application? Also, I just want to thank you again for all of the attention that you have been giving this problem.

07-30-2008, 08:17 AM
Please delete this post.

07-30-2008, 08:29 AM
You're right- I meant grey wire, not blue. The grey wires supply the voltage and the blue and grey wires are the return lead. Black is the ground.

To check the TPS,

If you're able to read the voltage without removing the plugs, probe the blue wire and with the key ON, motor OFF, you need to move the throttle through it's entire range. You should see a voltage swing of ~ .7 VDC at idle to ~ 4.8 VDC at WOT (Wide Open Throttle). Move the throttle slowly and watch for any major dips. If you do see a major dip, the TPS needs further testing but a DVM doesn't react fast enough to see a short glitch.

To test the MAP sensor, probe the green wire with the plug in place. With the key ON, you should be able to see voltage on that wire. Start the motor and you should see ~ 1-1.5V at idle and ~ 4 VDC to 4.5 VDC at WOT.

08-02-2008, 08:52 AM
I was able to get back boat diagnostics yesterday afternoon and tested both the TPS and MAP sensors using pins run along the wires and into the connectors. With the motor off and key on, he blue wire on the TPS measured .672 vdc at idle and moved smoothly to 4.24 vdc at WOT, in both forward and reverse. I tested it several times moving the throttle very slowly and did not see any drop outs. Next I tested the light green wire (middle wire) on the MAP sensor with the motor running. It started at 4.16 v at idle but immediately jumped all over the place as I moved the throttle - something like .6, .9. 2.4, 1.5 - it jumped up and down with no consistent readings. Even leaving the throttle in one position, the voltage varied all over the place. I even tried moving the pin to make sure that I had a good connection but had the same symptoms. So do you think I have a bad MAP sensor?

08-02-2008, 12:04 PM
It sounds like it could be the problem. Do you know anyone who has a vacuum pump for bleeding brakes? If you do, remove hte connect the tube that comes with the pump to the sensor and with the key ON, look at the voltage again. It should start low and increase smoothly. If it doesn't vary smoothly, I would say that the sensor is bad. When you get to the the point of having a good amount of vacuum, you should see the higher voltage you did at idle. You can get this part at any good auto parts store.

08-03-2008, 09:37 AM
I took a chance on the MAP sensor and replaced it. Unfortunately, the new sensor acted just like the old one. The volatages on the light green center wire are still jumping all over the place. Even when the throttle is held in one position (engine running) and I put the DVM on the the range to read just tenths of a volt, the readings are constantly jumping from .5 v to 2.5 v. Within the span of a couple of seconds there may be four different readings. Taking the boat for a test drive confirmed that the new MAP sensor had no effect... still the same lugging down like it was getting to much fuel or not enough air. Thinking about the air, when I got back to the boat lift, I did try something new. I pulled the air cleaner and held a mirror so that I could see the butterfly valves. With the engine off, I move the throttle from idle to WOT. At idle, the butterfly valves were closed and at WOT they were wide open. I repeated the test with the engine running and at idle they were closed as you would expect. As I moved the throttle, however, they never changed position... stayed closed even at WOT. Thinking now of the MAS, I checked for voltages on the 4 wire plug with it unplugged and the engine running. The grey wire with the white strip and the grey wire with the dark strip both have voltages jumping around
.5 to 11.6 volts. With the plug back in place and the engine running, the light green with the white strip and the green wire with the dark strip both had output voltages varying from 11.6 volts at idle and going to 12.3v as the throttle was advanced. At whatever point I stopped the throttle, the voltage would read 12.3 and then drop to 1.1 v and stay there. With the engine running, the butterfly valves always appear to be closed regardless of the throttle setting. Even at WOT they appear to be fully closed. Any thoughts?

08-03-2008, 11:49 AM
What "butterfly valves" are you referring to, and what is the MAS? If you look at the throttle body with the flame arrestor off, you'll see one oval throttle plate attached to a rod that's controlled by a lever, which has the throttle cable attached to it. If you watch the end of the cable while you move the handle at the helm, it should open and close. You can do this manually at the motor by slipping the retaining sleeve back and releasing the cable from the lever on the throttle body. Start it, rev it and watch the voltage. If it revs normally, look for a small clamp that holds the black sleeve for the throttle cable in place- is it loose, tight or missing?

What are you calling the MAS- Mass Airflow Sensor? Your motor doesn't have one. Can you post a photo of this?

I didn't mention it before but any test done in neutral has to be repeated in gear. I neutral, the motor has no load .

Re: the jumping voltages- wiggle the two large plugs on the ECM to see if this changes. If it does, the ECM pins or hplug terminals could be corroded or may have spread.

This is the kind of situation where being at the boat would make diagnosing the problems a whole lot easier.

08-04-2008, 08:41 AM
Jim... sorry for the bad terminology. With the flame arrestor off and looking back into the oval opening with a mirror, I was looking at what I believe that you are referring to as the throttle plates. They are two plates, each about the size of a silver dollar, that are attached to the lever with the throttle cable attached to it. With the engine off, these plates are closed at idle and wide open at WOT, which is what I would expect. However, with the engine running, these plates are always closed, even at WOT. So back to the IAC (which I was mistakenly call the MAS). The voltages on the four wires that I described in my previous post, were taken with the boat on my lift with the engine running but out of gear. I assume that the IAC motor controls the throttle plates. Could it be keeping them closed at full throttle, causing the engine to starve for air? Also, if you recommend it, I could hook up a hose to the engine so that I could repeat the voltage tests on the TPS, and IAC while in gear. I have plugged and unplugged the connectors on the EMC, but will take a closer looks at them today. By the way, based on the style of the MAP sensor that I purchased, I believe that this it is a '96 LT1 engine in my '98 Maristar. Is that common?

ProTour X9
08-04-2008, 09:29 AM
Sorry I just read the first post but, we had the vette LT-1 and it would bog down, we replaced the impeller and never had the problem again.

08-04-2008, 11:35 AM
You control the throttle plates, which are supposed to move when you move the lever at the helm. If they stay closed when the motor runs and you advance the throttle, there's a mechanical problem, not electrical. Go to the motor and with it not running, release the throttle cable the way I described before. Now, move the throttle lever with the ball on it and see if you can make the plates wiggle when you press on them. If you can, the screws need to be tightened, or the pawl (the part with the ball on it) needs to be fastened better, That should have a hole that matches the end of a rod, and a screw that goes into the end to keep it in place.

The four wire harness near the base of the throttle body should have a pair of green wires anda a pair of light blue wires, with one of each having a white or black tracer. The IAC doesn't control the throttle- that would be throttle by wire anad they didn't come out with that until later. The IAC (Idle Air Control) does what the name indicates- controls the idle speed when the throttle plate(s) closes, with the secondary function of opening to add some air on hard acceleration and close when the throttle is shut quickly, in order to "follow" the throttle's position and make response snappier. If you try to measure the voltage on those wires, you need to use each pair, not reference to the block. One pair opens the IAC and the other pair closes it.

08-07-2008, 07:33 PM
Jim... I considered your statement about having to repeat all of the test under load to get accurate readings and decided that I could not invest any more time trying to diagnosis the problem and still hope to get some enjoyment out of my boat before summer is over. So I bit the bullet and took it into Action Water Sports today. They did a lake test with a diagnostic computer hooked up and saw that the exhause pressure was high. They decided that the problem something in the muffler obstructing exhaust flow. I immediately thought about mouse nests or bees nests from it being in storage but was told that those were not likely and that the obstruction could not be removed because of the internal construction of the muffler. That didn't make sense to me but I feel like I am over a barrel here. The boat only has 350 hours on it and so far I have had to put about $8K into repairs. That doesn't seem to track to the quality that I thought I was purchasing with Mastercraft. I wish there was a corporate program to review maintenace history from end users to improve overall quality. Hopefully, however, this will get the boat going again for this season. I did want to thank you again for taking the time to work with me over the last few weeks. I really did appreciate your input. I'll do one last post when I get the boat back and test the performance.

08-07-2008, 07:53 PM
First of all, I have never heard that there was a way to tell if there is excessive exhaust pressure on an LT-1. There is no sensor for that.

Second, the mufflers are pretty simple. If the muffler was removed, any obstruction could be seen by using a light and maybe a small inspection mirror.

This isn't freakin' rocket science, it's a fargin' car motor! If you want to tell them I said this, go ahead and if they want to come here to defend themselves, they should. I have heard that their service was really good but to say that they saw high exhaust pressure on that motor by using a diagnostic computer is BS. If anything, the MAP sensor may not be showing the correct range but again, there's no sensor for the exhaust system, in-cylinder temperature, compression, air mass, intake air temperature or anything other than crank position, throttle position, vacuum (MAP sensor), RPM, coolant temperature and total advance.

Sticking a wire into the muffler might drag whatever is blocking the flow out, if that's the actual cause. For future reference, the exhaust flap(s) should be taped shut when the boat is winterized.

08-09-2008, 04:30 PM
Holy crap!!!! I hope you haven't spent any real money yet. I have been following this thread for the last couple of day's and tride everything along with some other threads. I have had the same exact problem on 2002 X-Star, w/ same carter fuel modual. I have taken it to the dealer and was told replace it the fuel pump is bad at $450 bucks. I then read some other threads about replacement fuel pumps and purchased e2400 from advanced auto $76.00 bucks. Still didn't get more than 22 mph and bog down after half throttle. I couldn't understand this so I pulled the regulator out of the of the housing so that I could see in side when it was running, I like to see how things work, I found that that peace of S%@$ Mother Fnnn fuel line was kink when you push it all together. I went back to advanced spent $1.26 on a new fuel hose, installed it and it runs like a champ.

08-10-2008, 10:09 PM
Jim... I took a look at the muffler and found that both outlet ports were totally blocked with the internal fiberglass baffel. It was pressed so hard against the base of the outlet ports that I could not move it at all when pressing down with a screw driver nor could I get ANY air to blow through the ports. It took me only a couple of minutes to drill through both obstructions with a hole saw which would have solved the air flow problem (even though it might have been a little louder, it would have saved me a thousand dollars). I got to thinking about how the baffel would have gotten pressed so hard against the ports that it sealed them and it occur to me that it could have been ice damage since the problem occurred right after Action winterized my boat and stored it for me. Do you think that if the muffler drain plug was not removed and water remained in it that ice could have pushed the baffel against the outlet ports? Should I send the muffler back to Mastercraft for someone to analyze the problem? Or is this a common problem? From a quality perspective, I would think that it would be valuable to understand what was causing the failure. I would appreciate any thoughts that you have on the matter.

08-10-2008, 11:03 PM
Squeeze the exhaust hoses. If you can flatten them easily, it overheated. If you ever had the occasion to squeeze them last year and they were more rigid, it's not just a coincidence. If the baffles were in place as if they were adhered with resin, my opinion is that they dislodged and were forced against the outlet, where the heat softened the resin and since it was dry, it more or less welded them in place. I can see how raw water could have broken them loose and then the heat welded them in place.

Now that we know what the blockage is, I can say without hesitation that this boat wouldn't have been used for 350 hours with this problem. I can also say that if someone charged you $8K and didn't find the problem, you need to go back to them and explain why they should adjust your bill. I would start asking some serious questions about this, such as:

Why did you (the service shop) not find this problem?

Did you remove the plugs from the muffler?

What else didn't you do when you winterized the boat?