GT40 intermittent rough running

Was the red light on the top of the dash lit up? If the engine overheats or loses oil pressure (less than 5 psi), it will go into "limp-home" mode which will not allow the engine to run above 2700 rpm.

What were your temperature and oil pressure readings when the boat lost power?

The following is taken directly from the PCM GT40 EFI owners manual (page FM 4,5):

"In the event of a water temperature overheat (200°F or higher) or loss of oil pressure (below 5 PSI), engine operation will noticeably change. The ECA will alter the injector timing sequence, the engine will run rough, and engine speed will drop to 2700 RPM. Below 2700 RPM the engine will run normally, but not above. The engine will remain in this Speed Limiting Operation Warning (S.L.O.W.) mode as long as the cooling/ oil pressure problem exists. After the problem is corrected and water temperature or oil pressure returns to normal, the ECA will automatically allow the engine to resume proper operation. The ignition switch does not have to be turned off to reset the system."

Has the boat always run well up until this point?

Cooper

Hi Cooper,

There are no alerts / alarms to signify SLOW mode. The issue can be quite volatile, meaning rough running/clear/ rough in just a span of seconds.

On the antisiphon valve, can someone point me to the part? i did a search on nautiqueparts.com and came up with nothing. Is this a replacement or clear /repair?

thanks!
Charles

I just solved a similar issue with our boat. I'd pull the fuel pickup tube right out of the tank. The filter at the end of ours was completely clogged to the point that fuel stuck in the tube couldn't drain back out once it was out of the tank.

Fuel pressure was 34-32

That engine sure sounds like it is not running on all 8 cylinders. Have you checked your plug leads to the firing order. You may have inadvertently swapped a couple while replacing plug wires.

If the firing order is correct. I would then remove the plug leads one at a time. This will isolate what plugs are firing and any that are not.(The engine will run rougher when you remove a good firing plug lead)

Check quality of spark you should have nice fat blue spark at plugs.

I also heard a couple of noises I did not like the sound off. I could just be damper rattle in gear due to the rough running at low rpm.

Get back to us once you confirm the above.

I think Lewy is on the right path as usual.

That is a perfectly timed miss, which to me, suggests an ignition problem. Definitely sounds like a cylinder not firing. I'd be checking for mixed up spark plug wires and wires not completely seated on the cap or plug.

cgofort (or name not give as Pete would say,

When you are looking at the video in Youtube, press the "Share" button, this will serve up the direct link to the video, so copy that link. Sometimes, the link you'll be watching it through is from a subscription, featured video etc. Those links often don't work. You want that "Share" link.

Then, take the link and put in between these {tube}http://youtu.be/I7fK8-ntZXo{/tube}

Now, replace the squiggle brackets { with the square brackets [, and you've got it.

Coil is possible? I'm not familiar with that one really. Relays are another strong possibility.

Thanks for the direction on embedding videos.

Here's the boat yesterday during trailer load, right AFTER earlier videos:


To answer above question FCC: yep, it has FCC. I replaced the filter there.

I've owned the boat almost 1 year. Previous owner replaced low pressure fuel pump before I got it (allegedly).

cgofort wrote: I really WISH the cables were in incorrect order, but because I'm no expert wrench, I numbered all the plug wires and the respective connection to the cap. All of those are aligned. What gets me on this issue, it runs flawlessly for 10 minutes, but then once it heats up, it starts to go bad. Would a failing coil produce this sort of situation? Video was taken yesterday. What is odd, i turned the boat off to get trailer and load it. In the time that took (maybe 10 minutes) the engine started smoothly. I can post that video. Can someone give me hint how to embed the video so i'm not just showing links? Thanks, Charles

Charles I would check fuel pressure when the engine is running rough. This is so you can rule out fuel supply being the cause of intermittent problem. Next I would check the quality of spark at plugs when running rough if you can get an idea of the nice fat blue spark when it is running correctly to compare it would be good.

It could be the TFI module or coil firstly I would clean all the connections to both and then test. The code reader may be a real help here and at their price probably cheaper than any part you are going to replace. GT40 Code Reader

I couldn't figure it out, and was done throwing parts at it. I sent the boat over to local marine shop. After 2 weeks, they believe it is related to the computer. Will see.

Nice posting guys! Good info here.

solved!!!
This would be a very tough issue to identify unless you're super with electrical diagrams and know what you're doing.

Short answer: corrosion in the fuel injector harness caused the injectors to OHM out, making them shut down. Injector harness was testing at 30 OHM, should be no more than 12 OHM.

Mechanic cleaned harness and replaced corroded connectors inside the harness. Boat works great!

Of course, this took a long time to track down, mechanic swapped the ECM, distributor assembly, cleaned injectors, etc, etc so after 3+ days of labor charges, it's finally fixed, just a huge punch in the wallet. Glad to have it back, and hope this will help anyone in future.

Thank you for taking the time to document this issue