350 mag mpi back to running rich on cold start

C

cappie

Cadet
Joined
Apr 4, 2009
Messages
13
Changed IAC and coolant temp sensor. Cleaned throttle body, quickleen in fuel. did a complete tune up and it worked for a few start ups. Now it is back to running very rich on start ups. Once it warms up it clears up.

Any ideas would be great
 
J

joncrisler

Petty Officer 2nd Class
Joined
Sep 25, 2009
Messages
150
Re: 350 mag mpi back to running rich on cold start

I thought engines were supposed to run rich when cold :)
That said, you hit the obvious things I would have checked. Has the engine harness been altered / repaired ? I wonder if a wiring problem is affecting your engine readings. Also, what year? would there be an EFI firmware update that would be appropriate ?
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: 350 mag mpi back to running rich on cold start

Merc has been making 350 Mag MPI engines since 95, and they are not all the same.
Got a SN for your engine
 
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