1999 MIE 7.4 MPI ECM Parameter's

[waterbug]

Hey guys, sorry for the delay. It has been a little hectic around here with the virus stuff going around. Hope you and your families are all well.

I checked the position of the throttle plate vs. throttle position at helm. Both are equal however there is a noticeable difference under way. Several degrees difference. I will check TPS with scanner as soon as I can.
I disconnected the "add-on" pumps and the original pumps were able to produce 40lbs steady at key on. Reconnected the "add-on" pumps and both maintain 40lbs. Will test underway as soon as I can.

As for the solenoid, STBD has a wire corroded completely off. So it has to be stuck in the "open" position because that engine actually runs better than the one with the "newer" solenoid.

I will do more testing and post as soon as I can. Stay safe out there and as always, thanks for all your input!

[waterbug]

Update. I was finally able to get all the work done. Both engines running great now. The main culprit was the fuel pressure regulator. Oil/water (condensation)was able to creep down the vacuum line and cause corrosion. The injectors were dirty/clogged/stuck. (I just had them sent for cleaning because they had never had it and that was the diagnosis from the company) now they all flow within 2cc of each other. The cap and rotor button were functioning but did have corrosion and wear so they were replaced. The MAP sensor, while was still reading accurately was dirty so it was replaced. As for the additional/auxiliary fuel pump the wiring for it ties directly into the factory wiring harness with no splices. The fuel pumps were replaced because why not, since it is a cool fuel 2 and accessibility is poor. Runs like a champ now topping out around 4200rpm and holding steady. Thanks for all your help!

[bud37]

Thanks for posting the resolution....you did a great job figuring it out.....

[Oldie]

Okay, I just had a crash course in Marine ECMs', and wow, they are totally different to cars!!

The advantage you have is that you have 2 motors, one working, and one quirky..... it's "parts swap" time, to narrow it down. From your description, since it's not throwing codes and you're not going into limp mode, your MEFI is just picking a code based on the sensor inputs. As a guess, I would suspect your TPS. The carbon track could be faulty and sending the wrong Voltage to the ECM, and it thinks you have just throttled back, so picks an appropriate setting from the chart?
If it's a simple task, I would swap them out. I wouldn't try a Volt/Ohm meter in a static test, but rather a real world scenario. Continue swapping out easily accessible sensors, and see if your starboard motor now adopts the problem.

You mentioned that you checked the spark plugs and they seemed normal. Does this mean the were a nice tan colour, and not white or black? If they compare favorably (colour wise) to the good motor, this would indicate a healthy motor and MEFI, but it's just getting the wrong inputs. If they are white (lean) I would get professional help, to avoid destroying an engine.

Cheers.