Mercruiser 4.3l EFI Idling issues

[Dan F.]

Hey yall. Well after another successful rebuild after my last rod knock thread I have recently developed an Idle issue with this 2000 model motor. Runs fine at idle then starts to break up till the ECM kicks up the idle momentarily then runs fine again till the break-up starts again. Even stalls on occassion. Was told there was a filter screen behind the IAC motor that may be carboned up but there ain't one in there. Replaced IAC motor since the motor runs great with a little idle bump but that had no change to the idle problem. Any ideas? Idles at about 700-750 rpms on the trailer so low idle concern isn't a problem. Not about to start shotgunning sensors at it without good reason. Figured with the wealth of knowledge here,someone may have a clue what to look for. Oh yea,no water in both filters either so that ain't it!

 

[achris]

Re: Mercruiser 4.3l EFI Idling issues

Water reversion... If you run those engines at idle on flushers, they suck water back into the cylinders... The ECU is detecting the RPM drop and kicking the engine, hence the rise... Put the boat IN the water and check it... You'll probably find it's ok...

It's in the owners manual about lifting the idle speed (using the fast idle on the control box) to 1300 +/-100 when running them on flushers....

Chris........

 

[Dan F.]

Re: Mercruiser 4.3l EFI Idling issues

Water reversion? Is this caused by the lack of exhaust backpressure while running the engine on the trailer? Gonna float it down the bayou here in a little bit and will report the findings. Appreciate the advice man and hope your dead on right cause I don't need any more headaches this month.

 

[achris]

Re: Mercruiser 4.3l EFI Idling issues

Water reversion? Is this caused by the lack of exhaust backpressure while running the engine on the trailer?

Yes...

Gonna float it down the bayou here in a little bit and will report the findings. Appreciate the advice man and hope your dead on right cause I don't need any more headaches this month.

Me too...

 

[Dan F.]

Re: Mercruiser 4.3l EFI Idling issues

Well that seemed to take care of it Chris. A little stumble before it reached peak operating temperature but it went away. Might be swelled vacuum line to pvc valve but other than that it ran fine,thanks man. I'll hoist a cold one in your honor this evening! Throw another Kangaroo on the Barbie!

 

[darooster930]

Re: Mercruiser 4.3l EFI Idling issues

Im having an issue with a 2002 500 mercruiser, but what happens is when i put it into geat the idle goes way up, use to settle down with in a few secs, but not is taking longer, wont do it out of the water with no load, nor will moving the throttle change it, the IAC motor?, could that be my problem? Im located in a romote area, lake powell, only one shop has a reader, but no codes came up, they are baffled, i have twins, but the other motor runs fine.

 

[Don S]

Re: Mercruiser 4.3l EFI Idling issues

Welcome to iboats darooster, You need to start a new thread of your own when you have a problem. Not hijack someone elses old thread.

 

[darooster930]

Re: Mercruiser 4.3l EFI Idling issues

Im having an issue with a 2002 500 mercruiser, but what happens is when i put it into geat the idle goes way up, use to settle down with in a few secs, but not is taking longer, wont do it out of the water with no load, nor will moving the throttle change it, the IAC motor?, could that be my problem? Im located in a romote area, lake powell, only one shop has a reader, but no codes came up, they are baffled, i have twins, but the other motor runs fine.

sorry, new to this site........yours was the closest to my problem, thought you might know something, thanks for the advice