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Mercruiser 502 MPI cutting out

Old 05-29-2007, 06:10 PM
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Join Date: Aug 2002
Location: Roanoke VA
My Boats: 1986 Formula 357-SR1
Posts: 266
Mercruiser 502 MPI cutting out

A problem cropped up this weekend: When cruising on plane my port engine started cutting out. I first noticed it stumbling occasionally, then it started dying completely. When I stopped, sometimes I could turn the key off, then back on and it will start immediately. Other times the ECM and fuel pump would cycle up, eng will turn over but not start. A few minutes later it usually would start again. I started with the easy fix- changed the water/fuel filter- no help of course. The next day I turned the key- nothing powered up. I left the key on and started jiggling and pushing on the electrical connectors- when I touched the coil wires- the eng cycled up and then would start. The connectors still have lube in them and look in no way rusted or corroded. I managed to get the boat home with it stumbling occasionally and dying a couple of times but obviously it wasn't just a loose connection. I felt the coil when I got home and it wasn't hot like they are supposed to get when they fail. Anybody out there have any suggestions??
ctuck0659 is offline  
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Old 05-29-2007, 06:18 PM
Join Date: Aug 2005
Location: sint maarten
My Boats: 96 , cig top gun
Posts: 1,491

yes... in the absence of a scanner to help diagnose it properly, just start swapping parts one at a time to the other motor. when the other motor does it, thats what was wrong.
stevesxm is offline  
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Old 05-29-2007, 11:06 PM
Join Date: Jul 2005
Location: evansville In
My Boats: '94 29' powerquest
Posts: 482

Hey ctuck, Look very carefully at your main harness connector on the back of the motor. Turn your key on and wiggle this connector in and out ..kinda slow so you can get it to act up. I have seen this very thing several times. Good luck
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