mercruiser 7.4 mpi starts and dies?????

[Michael C. Beam]

I have a 1996 mercruiser 330 hp w/a 7.4 MPI. When started at a idle, itfires up and quickly dies. If you give it a little throttle and fire it up it will stay running, but if you idle it down to shift it into gear before it's warm the engine will die. Other than that the boat runs perfect, 60mph at full throttle 5000 rpm. Can anyone help. Thank You, Mike

 

[Haut Medoc]

Re: mercruiser 7.4 mpi starts and dies?????

Sounds like a choke issue, possibly....
If you need to give it a little gas to start it & you can keep it at less than 1000 rpms until it is fully warmed up & it will idle after warmed up, it sounds normal for a carbed engine to me....
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[Windykid]

Re: mercruiser 7.4 mpi starts and dies?????

Next question, when warm what RPM is idle set at??

 

[Mischief Managed]

Re: mercruiser 7.4 mpi starts and dies?????

choke on an MPI?

I'd look at the IAC (Idle air control) valve, it's on the throttle body, below and between the two big passages; and the ECT (engine coolant temperature) sensor on the thermostat housing. Maybe the wiring is a loose. A scantool would be handy...

 

[Reel Poor]

Re: mercruiser 7.4 mpi starts and dies?????

A scantool would be handy...

And is most likely going to be necessary. BTW, do not try to adjust the idle speed. Idle speed is controled by the ECM.

 

[Michael C. Beam]

Re: mercruiser 7.4 mpi starts and dies?????

Thanks for all of your info. Your right though a MPI engine does not have a choke, does anyone know what kind of scanner will work on this engine. I thought these had to be trouble shot with a lap top and the program from Mercruiser?

 

[Reel Poor]

Re: mercruiser 7.4 mpi starts and dies?????

You could make one of these to read codes. You could also look HERE for a choice of the proper diagnostic aids. If you get the codes out of it (if there is any) come back and let know what code(s) you have and we can go from there.

 

[Don S]

Re: mercruiser 7.4 mpi starts and dies?????

I don't know about you other guys. But in my experience, probably 9 out of 10 times I don't see set codes that help me find the problem. You do need to check, but it all comes down to testing and following a systiatic approch to troubleshooting the EFI systems.
Get the OEM manual and start reading, studying, testing and following instructions. And you MUST know how to use a DVM, EFI fuel pressure gauges, and read wiring diagrams.

 

[Reel Poor]

Re: mercruiser 7.4 mpi starts and dies?????

I don't know about you other guys. But in my experience, probably 9 out of 10 times I don't see set codes that help me find the problem.

I agree, sometimes the codes that DON'T set can help more than the one's that do. The ability to read live data is probably the most helpful tool. Along with the DVOM and th fuel pressure gauge you mentioned.

 

[newport dave]

Re: mercruiser 7.4 mpi starts and dies?????

Don is spot on as usual. The GM MEFI "self diagnostic" system leaves a lot to be desired, and following diagnostic procedures in the factory service manual is the way most EFI problems will be diagnosed and repaired.

The newer ECM/PCM555 systems have a much better self diagnostic system, but don't let you view as many data parameters.

If I was going to take a guess at what the problem is on this engine, I would vote bad IAC motor.

Dave

 

[brooksdonald]

Re: mercruiser 7.4 mpi starts and dies?????

I would recommend replacing the IAC valve. You shouldn't have to give it any throttle to start if the IAC is working correctly. I did this last month and it solved my problem (which was identical to yours).

 

[Don S]

Re: mercruiser 7.4 mpi starts and dies?????

I would recommend troubleshooting. Throwing parts at a problem because it fixed someone elses problem is a waste of time. The same problem could be from a wire going to the IAC, and not the IAC itself.