6.2L MPI - slow cold idle. How do you test ECT and IAC?

I

iammarcuse

Petty Officer 2nd Class
Joined
Oct 15, 2007
Messages
131
I have a 2004 6.2L MPI Mercruiser serial number OM695430. It runs perfectly except for a slow idle when cold. After cold starting it idles at only 500 RPM and will stall if you put it in gear. When the engine warms up it idles at 600 and runs flawlessly after that. Manual #31 says to check the IAC (Idle Air Control) and ECT (Engine Coolant Temperature sensor) but does not say how and gives no testing parameters. Does anyone know what ohms it should read hot or cold, or where to find how to test these sensors? Any help appreciated. Thanks.
 
M

muc

"Retired" Association of Marine Technicians...
Joined
Jul 7, 2004
Messages
2,064
Re: 6.2L MPI - slow cold idle. How do you test ECT and IAC?

Manual #36 covers the ECM 555 stuff.
Don’t know how to test them, I hook up a scan tool and it tells me what temp the sender is seeing and allows me to control the IAC to see how it’s working. The manual might have non scan tool info you could use.
 
I

iammarcuse

Petty Officer 2nd Class
Joined
Oct 15, 2007
Messages
131
Re: 6.2L MPI - slow cold idle. How do you test ECT and IAC?

Thanks for the tip but I do not have the scan tool. expensive touch
 
I

iammarcuse

Petty Officer 2nd Class
Joined
Oct 15, 2007
Messages
131
Re: 6.2L MPI - slow cold idle. How do you test ECT and IAC?

Anybody else know the parameters of these sensors?
 
M

muc

"Retired" Association of Marine Technicians...
Joined
Jul 7, 2004
Messages
2,064
Re: 6.2L MPI - slow cold idle. How do you test ECT and IAC?

MANUAL #36 page 3A-24 has the resistance test for the ECT.
The IAC can’t be tested with meter. Manual #23 page 5E-90 tells how IAC’s were tested in the early days of MEFI ECM’s. Might help you?
P.S. if your IAC is bad, might want to want to replace your IAC muffler. It seems to me that plugged IAC mufflers seem to be causing IAC’s to go bad. Almost all of them that I find bad have a plugged muffler. They cost a little over $1.00 and are easy to replace.
 
I

iammarcuse

Petty Officer 2nd Class
Joined
Oct 15, 2007
Messages
131
Re: 6.2L MPI - slow cold idle. How do you test ECT and IAC?

Wow, great information. Not sure how you knew where to look, but thank you. I have manual #31 and none of that is included. I'll give it a go.
 
I

iammarcuse

Petty Officer 2nd Class
Joined
Oct 15, 2007
Messages
131
Re: 6.2L MPI - slow cold idle. How do you test ECT and IAC?

Well, Muc you rock. I simply swapped out the IAC muffler which was hard and black and the thing idled perfectly cold. It just wasn't getting enough air to the IAC. Dealer had to order the part, said he had never sold one. Must be some poor running motors out there.
 
You must log in or register to reply here.
Top