need help with strange 7.4MPI problem

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08-03-2009, 06:58 PM

#31

tomtc

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Quote:

Originally Posted by dbkski

tomtc - I did not mean the boat. I am talking specifically
what is wrong with the ECU/ECM? Programming error?
Something caused your engine to perform poorly. I am
thinking of the next guy who may have the same situation.
If he knows what chain of events brought your engine's
ECU down it would save him time. My Cobalt is a '99 and
came with a 7.4L MPI. It ran perfectly until the day I sold
it and dropped in the 502. I am sure someone knows the
real story of the "bad ECUs". Did your low voltage issue
cause bad info to get stored in the ECU never to be
overwritten? As a programmer I am often told to chase down
a "programming error" or "fix a bad program". I laugh to
myself since it is always something else. Now I get that
most mechanics or owners don't really care what the real
problem with the boat was just that it runs well and only
cost a few $100's. I am just looking for info from someone
who knows the Merc MEFI ECU's and the real cause of
your engine's problem.

There is no way to know definitively know what failed in the ECM though, as I said, it appears to be one of the injector drivers based on the symptoms. There is also no way to know what caused the failure though I suspect that it was a electronic component (mosfet, etc.) in the driver circuit and that the failure was not related to any specific cause and effect. The programming check code is unchanged and correct so it is highly unlikely that it was a programming error or overwrite. Remember that the ECM contains a lot of circuitry beyond just a computer, any of which can fail.

Last edited by tomtc; 08-03-2009 at 07:09 PM.