F115 idlle trouble shooting

[loyoki]

Thank you for your answers about VST.
I have just replaced crank shaft gasket on my F115 because of water in cylinder and oil, I cleaned also injectors(they work perfectly) and valves and salt in crank shaft (all that can be cleaned !), it is like new now. Before I do this job my F115 ran perfectly at idle. Now it runs perfectly and better (more power) at mid range and full power, like it has never ran before.
But at low rpm I have problem with idle, randomly. Rpm increases to 900 and decreases to 600 randomly, and sometimes motor dies. It seems that electronic try to maintain the good idle (before it was 700 rpm stable).
When I start it again, no problem, idle remains stable (700) and then, after a few minutes, problem remains.
I saw on this forum the same problem and it seems to be filter in VST, it is why I asked the question (see post "what is VST?")
BUT perhaps, someone has another idea ?
Many thanks
Lo?c
FRANCE

 

[Casco Bay Outrage]

Re: F115 idlle trouble shooting

Your idle problem sound very much like mine.

Watch my thread for information.

http://forums.iboats.com/showthread.php?t=297214

 

[loyoki]

Re: F115 idlle trouble shooting

Thanks Casco,

Yes I had already seen your post and I think it is the same problem.
But in fact, I am french, and I have problem to understand US abbreviations.
TPS ? I think it is the elctric air contol above intake
ISC ? What is it and where
ECT ?

Do you have solve your problem ?

Thanks

 

[jaymz101]

Re: F115 idlle trouble shooting

The TPS is the Throttle Position Sensor. On the F115 its starboard side close to the front of the flywheel. Has 3 wires going to it, Pink, Black, and Orange.

ISC is the Idle Speed Control Valve - located lower on the same side as the TPS. ISC is plugged into a 6 pin connector.

And I think you mean ECM not ECT, correct? Thats the Electronic Control Module (the computer). I very much doubt it's a problem there.

Its probably a poorly adjusted TPS.

 

[loyoki]

Re: F115 idlle trouble shooting

OK thanks.
With your advices, yesterday I adjusted the TPS, OK it is very sensible, just a very very little turn and rpm goes up to 1200 or down to 500. I adjusted it to 700, but it was at the same place (there was paint marks).
Sarted it again, iddle fine (700), gone up to 3000/4000 rpm and same problem, idle hesitated, gone down to 500 and died.
Even between 2000 and 3000, motor throttled alone ???
So, I removed ISC: it was smoky and black grease, I cleaned it with alcohol 90..
Sart engine again: engine idles perfectly, do not hesitate in higher rpm and throttles regurlaly.
I think my problem is solved but I think I have to clean VST filter one of these days.
Many thanks