Engine hunts then dies at idle or slow speed.

[vortech347]

My 99 Sport w/GT-40 has had this problem almost since day one. It happens 9 out of 10 times we take the boat out.

During warm up it does not occur, only after the engine reaches operating temperature. What happens is the engine will start "hunting" or revving up and down between 250rpm and 1500 rpm. I call it hunting because this was a common ailment of 5.0 liter Mustangs with similar FI systems.

While the boat was under warranty I had it in the shop 3 different times but the dealer was never able to completely fix the problem. They changed the throttle position sensor, the thermostat and did some diagnostics but were unable to recreate the problem when lake testing the boat.

Now the boat is out of warranty and I really want to fix the problem. It's very annoying to be idling in gear up to a downed rider and have the boat die. Nevermind, the fact that I spent 40k on a premier brand to have it constantly acting up.

Any ideas? I plan to talk to my dealer to see if they are willing to look at it and see if PCM or CC will honor it under warranty but I'm not paying them to diagnose a problem they couldn't figure out during the warranty period.

I'm not angry with my dealer because they tried to fix the problem. It's just one of those problems that doesn't always show up and it usually takes a while for it to manifest. I doubt the dealer stayed out on the water simulating a day of riding till it showed up.

Thanks in advance.

Greg

[tryan]

actually, since you have a previous complaint while under warranty and the issue has never been resolved, you might go a little higher in the food chain. most car dealerships have 'goodwill repairs' for vehicles out of warrenty. being nice will get you far.


get a flush pro and go to a ford dealership. find the best mechanic and tell him you will pay him double his pay scale (plus a six pack) to go to the lake with you for an hour after quitting time or fire it up at his house with the flush pro. ask him if he can bring the ngsII machine if the boat has an obdi port. it will be worth the 50 bucks.

1.)i would clean the air idle control motor and pull the plugs to look for an offending cylinder.
2.)install a remote fuel pressure gauge. it might be a fuel pressure issue.

3.)spray some wd-40 around the intake to look for a vacume leak.


the last gas ford motor i had would have a slight build up behind the butterfly next to the MAP port. this would make the idle unsteady, but not to the extremes you have. i always disconnected the battery to reset the computer, but i don't think there is a feedback loop on a boat motor.

[skinautique]

maybe an issue with a computer? Or it could be with one of the connections that is on the back near the computer. Don't know how to describe it but you could wiggle one of those to try to find out while it is running.

[vortech347]

Thanks for the responses. I think it is the IAC motor causing the problem. The dealer checked and verified proper fuel pressure. Unfortunately the IAC is a mrine unit that is different than the one that Ford put on cars with the same FI. I will first try cleaning it.

I was just hoping someone on here has gone through this and had it diagnosed properly.

It's definitely not a connection problem or a computer problem. That would be a hole different ball of wax.

Thanks for the info.

[tryan]

clean the port on the intake when you get iac off also. (the dealer really should have spotted that.)

vw used orings to hold the injectors in on the old cis cars. bad o-rings (cracked, dry rotted or hard) would cause overcompensation. try a little flamable spray that won't damage rubber. you might find 'sea-foam at a small engine repair place.

the only when warm issue still throws a wrench in the works. try this message board if you are still having trouble. http://flatratetech.com/ubb/ultimate...ubb=forum;f=13
the board is run by ford mechanics.

[R-mallis]

i work at a ford dealer and i had the same problems with some of the older 302's and after roadtesting mant times with my scan tool and looking at all the sensors i found them to have a bad oxygen sensor. im not too familiar with fuel injection on boats but i would think that if they are fuel injected they would have an oxygen sensor on them. hope this might help
by the way, in my experience i've very rarely seen an iac valve cause the syptoms you are having

[tryan]

hey r-mallis, are the marine gt-40's closed loop? can you look that up on oasis?

[vortech347]

R-mallis,

The eec-iv system in our boats do not use o2 sensors due to the water cooled exhaust system. Water is pumped into the exhaust manifolds so an o2 sensor would not function.

I am quite familliar with the problems with the 5.0 liters having had several Mustangs. The two ways to correct the problem were o2 sensors and to work on the iac. Either by cleaning, replacing or installing an iac adjustment plate that was a TSB from Ford would usually fix the problem.

Thanks for the info.

[R-mallis]

ok so i would say they are open loop systems since there are no o2 sensors. so they never went to eec v on marine applications vortech?

[vortech347]

I'm not sure

I don't think they ever got to the eec-v version. Marine applications run 3-5 years behind the newest technology.

When Ford stopped producing the 351W, PCM and other marine manufacturers went all GM for their marine powerplants. It's a shame because the SOHC mod motors would make good marine engines.

[tryan]

any luck with the iac?

do you think your injectors need a cleaning?

[vortech347]

Haven't had a chance to work on the boat.

I work a lot of hours so I haven't had a chance to look at the boat yet or try cleaning the IAC.

I doubt it's the injectors because it is a sporadic problem and under throttle the boat runs perfectly.