Rough Idle/Stall after use

I have a 2002 196, gt-40 (350 hours). The boat idles very rough and sometimes stalls after it has been sitting for 45 minutes + after being run. If it stalls, it will start right back up but will idle rough and may stall a second time. It also smells like it is running rich during this rough idle/stall period. This only happens when the boat is hot, say after pulling 3 skiers in a row and then letting the boat sit at the dock for a while. Once I give it some throttle the idle will smooth out some and then once I give it throttle to pull the skier up the boat will operate fine. This problem seems to be getting progressively worse.
I have performed the following:
New fuel filter
New temperature sensor
New cap and rotor

Have you replaced plug wires? It sounds to me like a misfire is developing when the air under the engine cover gets hot and humid.

I would replace the wires. Those are the weakest part of the ignition system. I had an elusive miss on my boat that was solved with a new set of wires.

Just to be clear, is your boat engine a carbed, PCM 351W with GT40 heads?

Not necessesarrily. I'm on the crackberry so no long winded description of why. But believe me, plug wires are the weakest link on your ignition system.

Let me know if it fixes things. I'd post a better discussion as to why I believe it will fix your problem if I was on a computer instead of the crackberry.

IF you are slightly technical, you may want to peruse the GT-40 service manual. It looks like if you follow it's diagnostic procedures you can figure out your problem...

Someone recommended that I also check the vent tube to the gas tank to make sure it wasn't clogged. I haven't had an opportunity to check it out but hopefully this week I will get to it. Vapor lock is supposed to be nearly impossible with the fuel control cell. I have tried running the blower and venting the engine cover but it doesn't seem to make a difference.

I checked out the Service Manual, the symptoms index suggests a number of possibilities in chart 3, 6 and maybe 10. I've checked out the easy ones, the other possibilities I'll likely have to have a PCM service tech check out for me. Before I do that, I'd like to see if there are any other possibilities to fix this. (The closest PCM tech is 150 miles away.) I will also try to figure out if the gas vent is clear.

I'm hoping there might be a likely suspect given the fact that this only happens after running the boat for a couple of hours then sitting for an hour. I'm in Colorado- hot sun, cold water, 80 degree air temp, very low humidity, 7200 feet above sea level.

The vapor lock theory is losing credibility with me after reading a few post and especially the one from Chris Broshar that said "vapor lock just doesn't happen on a boat".

I'll check out a few more things as suggested and report back.

You don't have to get the special cold spray. Regular old "Office Duster" is the same thing; just ignore the directions and hold the can upside down.

I'm going out Friday and I'm planning on a few tests and observations, but I'm starting to think it's the high pressure fuel pump that starting to go on me. I'm hypothesizing that the problem with the pump gets worse as the temp increases. I'm going to bring a can of compressed air to cool it down if the symptoms occur and see what happens.

I'm not really any closer to solving my problem, but it sure seems thermal related. I went out Friday, air temp in upper 70's and the symptoms were very minor. After running all morning, I opened to engine cover while at lunch, stalled only one on re-start and then ran fine. Yesterday it was a little cooler. I did even open the engine cover and not stall or idle roughly at all, it ran fine all day.

Does anyone know if it's common that when the fuel pump is starting to go, the problems are first noticeable at high temps?

The only thing I failed to mention in this thread is I put a new prop on while my other one is being repaired. It's an Acme 654 that seems to have better mid rpm speed, but less hole shot (requiring more throttle to get a skier up) than the original prop.

I talked to a tech at Skidim and he recommended that I measure fuel pressure when it runs fine and when it starts to act up. It is supposed to be up near 100's again by the end of the week so hopefully I will have a chance to look at that this week.

Hi,

Am just wondering if anyone found the exact cause of this issue?

I have a 97 Ski Nautique with GT-40 EFI and am having a very similar problem in that it starts and runs rough only after sitting for several minutes after use. On hotter days the problem seems to be worse.

Having tested much of the ignition system, I'm leaning towards there being a problem with the low or high pressure fuel pump that is temperature affected. I'm going to follow the advice in this post and try and test the fuel pressure before and during a rough start condition and go from there.

Pete

SNobsessed wrote: Maybe it is a fuel injector that leaks when it is hot.

Possible, however I had all the injectors tested and serviced about 8 months ago and they were all fine. Of course one could have developed this problem since then. How would I check for this? I would think I would need to pull out the plugs after running the engine and then letting it sit to examine them for excess fuel. Or I could put a fuel pressure tester on the fuel rail just after using the boat and monitor it to see if the pressure drops. Once the engine is off and the fuel pumps are off, how long should pressure stay in the fuel rails if all injectors are not leaking?

Pete

normally the pressure should hold for some time, it shouldnt drop off immediatly, there should be some sort of fuel pressure regulator in the system which maintains pressure. 100lbs sounds very high and usually you will find injected systems in the 40 to 60 lb range and the pressure will hold. i got bit hard on a car recently, it wouldnt kick AT all, new fuel pump, relay. ended up being the spark plugs. i took a new plug to check for spark and didnt pull the old one until this morning. its tough to figure this stuff out sometimes shooting in the dark. i have a scanner but it doesnt get you there. you may have to bite the bullet and take it in cause the next thing you will be doing is bying 8 injectors and it wont be that