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-   -   502 mpi won't idle down (https://www.offshoreonly.com/forums/general-q/216720-502-mpi-wont-idle-down.html)

cloudmaster_321 09-22-2009 10:35 AM

IAC has already been replaced with new, didn't fix anything. I troubleshot it originally, if I covered the hole in the secondary butterfly, the motor would stumble initially and then the IAC would open bringing in the alternate air. So even the old one was working imo. I'm thining it is a sensor problem that will have to be diagnosed with a scan tool. Something i may invest in if i plan on keeping this boat for a number of years. But for now, it's at the shop.

Young Performance 09-22-2009 12:31 PM

Did you check the area where the IAC seats. Although the IAC may be working fine, if it can not seal good against its seat, it will not close all the way. This is usually the problem with them. IAC's themselves rarely go bad. It is usually a buildup of carbon in the throttle body that stops them from closing all the way.
Eddie

FIXX 09-22-2009 12:46 PM

mrfixxall
 

Originally Posted by Young Performance (Post 2958073)
Did you check the area where the IAC seats. Although the IAC may be working fine, if it can not seal good against its seat, it will not close all the way. This is usually the problem with them. IAC's themselves rarely go bad. It is usually a buildup of carbon in the throttle body that stops them from closing all the way.
Eddie

Eddie, i think he has the older style IAC where the plunger seats in its own housing(ford style iac) not like the newer style merc efi engines..

cloudmaster_321 09-22-2009 01:15 PM

I had pulled the throttle body off and cleaned the whole thing down. The venturi the iac plunger goes into was clean. It is just a metal on metal contact from what i saw, and it was clean before and after pulling the body off.

FIXX 09-22-2009 01:39 PM

mrfixxall
 

Originally Posted by cloudmaster_321 (Post 2958109)
I had pulled the throttle body off and cleaned the whole thing down. The venturi the iac plunger goes into was clean. It is just a metal on metal contact from what i saw, and it was clean before and after pulling the body off.

check injector orings for vacume leaks!....

cloudmaster_321 09-22-2009 02:40 PM


Originally Posted by mrfixxall (Post 2958132)
check injector orings for vacume leaks!....

I never pulled the fuel rail. Just the plenum. Either way, here is an update from the shop:

Basically they verified what i had found, that the base timing was high at 14 degrees. They don't know what changed that it got there, but all they can tell me is that with the scanner on, and put into base timing mode, it was high. They put it back to 8 degrees, but liked the way the engine idled better at 9 degrees. They are going to do some more checking on other sensors and such, but they believe the timing is the whole problem. I would sure like to know how it changed. There was no way that distributer moved, the bolt was tight when i checked it.

I could have left it at 8 degrees as well, but I didn't see how if it was set at 8 before, it changed to 14 without some sort of sensor or something made it go to 14. I am being told that in base timing mode, outside sensors are no longer an influence. So, they are leaving it at 9 degrees.

obnoxus 09-22-2009 02:50 PM


Originally Posted by cloudmaster_321 (Post 2951847)
I tried running it with the air temp sensor unplugged, didn't seem to make a difference. But again, don't know if that's a good test.


water temp,,,on the goose neck,,,, unplugging it is what makes it act up,,,, check the pins to make sure they didnt pull back

FIXX 09-22-2009 02:51 PM

mrfixxall
 

Originally Posted by cloudmaster_321 (Post 2958182)
I never pulled the fuel rail. Just the plenum. Either way, here is an update from the shop:

Basically they verified what i had found, that the base timing was high at 14 degrees. They don't know what changed that it got there, but all they can tell me is that with the scanner on, and put into base timing mode, it was high. They put it back to 8 degrees, but liked the way the engine idled better at 9 degrees. They are going to do some more checking on other sensors and such, but they believe the timing is the whole problem. I would sure like to know how it changed. There was no way that distributer moved, the bolt was tight when i checked it.

I could have left it at 8 degrees as well, but I didn't see how if it was set at 8 before, it changed to 14 without some sort of sensor or something made it go to 14. I am being told that in base timing mode, outside sensors are no longer an influence. So, they are leaving it at 9 degrees.

Gotcha! how many hours on the engine?timing chain slip?

cloudmaster_321 09-22-2009 03:35 PM


Originally Posted by obnoxus (Post 2958190)
water temp,,,on the goose neck,,,, unplugging it is what makes it act up,,,, check the pins to make sure they didnt pull back

I tried that as well. No problems found with it............

cloudmaster_321 09-22-2009 03:36 PM


Originally Posted by mrfixxall (Post 2958191)
Gotcha! how many hours on the engine?timing chain slip?

20 hours, max........... Just rebuilt last fall.


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