MCM 5.7 EFI Problems when hot

[Dking81]

Hey I have a MCM 5.7 EFI (Throttle Body Injection) in my 89 Grady. During the first start up it runs perfect. After a day of trolling when heading in the motor will not run above 1500 rpm, if I try to run it more that it will fall flat on it's face and die.

What I have done so far : New cap and rotor, new plugs and wires, new fuel pump and reg., emptied and cleaned out fuel tank, installed fuel/water separator, and checked the grounds.

It seems to be related to when the motor gets warm. Any ideas??? Help Please!!!

 

[Don S]

Re: MCM 5.7 EFI Problems when hot

Time to hook up a diagnostic tool and see what the sensors are reading. Could be just a bad ECT sensor, says it's really hot when it isn't. OR, a number of other things.
Do you have a Mercruiser SN for your engine? As far as I remember, there wasn't any TBI systems on the 5.7's in 89.

 

[arks]

Re: MCM 5.7 EFI Problems when hot

As far as I remember, there wasn't any TBI systems on the 5.7's in 89.

You're correct Don (as always)- I'm betting it's not the original engine. I had the same engine installed new in a boat in 2000. I think Mercruiser stopped offering TB injection by 2001 or 2.

Yeah, have it analyzed before throwing $$$ away by guessing.

In my case, the engine developed a similar problem while under warranty. They replaced the ECM and ignition coil before solving it. I believe the problem was with the coil because it would get VERY hot afer running for awhile- so hot that black goo inside the coil was leaking out.

 

[Dking81]

Re: MCM 5.7 EFI Problems when hot

Hey,

Thanks guys, yeah it was a re-power and not the original engine. I know how to use a scan tool on a car, but where is the hook up on a boat? Can I use my auto scanner to read it? I see a terminal near the ECM that has a blank plug/cover in it.

I have also replaced the coil.

 

[Don S]

Re: MCM 5.7 EFI Problems when hot

No, an automotive scanner will not work on marine engines.

Still need to know what engine you have, is it Merc, or some other companies engine. That would have to be know to answers things like where do you hook it up and such.

Who knows what ECM it has and what scanner can be used.

 

[arks]

Re: MCM 5.7 EFI Problems when hot

Still need to know what engine you have, is it Merc, or some other companies engine.

Don- MCM means "MerCruiser Marine"!

 

[Don S]

Re: MCM 5.7 EFI Problems when hot

Don- MCM means "MerCruiser Marine"!

So that's what MCM stands for ................... would never have guessed that in a million years.

Stll don't have a SN to go buy.