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4.3L Mercruiser MPI problems

1

120mmAPFSDS

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After a failure to winterize two seasons ago, we've finally got a 4.3L Mercruiser MPI in a 2003 Crownline 180 BR running, but probably not as well as it should be. Last weekend, we resolved an issue with the fuel system and got it running once more. While running the engine to let seafoam through it and to clean it, the engine got pushed to 3000 RPM and then there was a pop from the bottom of the engine, and a puff of black smoke came out. We are at a total loss of what it could be: we're fairly confident it came from the bottom of the engine, it smelled like burnt plastic, we're not losing oil pressure, and now the engine sounds like it's got some grinding going on within. It doesn't sound good. Any assistance or insight would be appreciated. Ask for more information if necessary.

Thanks, Jacob
 
Docksidemarineservices said:
Post a video with good sound of the grinding.

Seafoam will damage the filters in the injectors.

Expand on the fuel system issue.
Click to expand...

Previously, a marine mechanic skipped the fuel cooler with another fuel pump from an entirely different boat. We believe this is because the first pump (the original) had become inadequate in supplying pressure, and he skipped the fuel cooler and just used the new one to push fuel. We're not sure as the mechanic didn't really tell. When we first started to try to get it running again, we had to figure out what the mechanic had done and replaced and we tried to figure out why. Once we figured out how it worked, we had difficulty (or we weren't intelligent enough) priming the fuel system due to the addition of the second fuel pump. Once we got it primed it cranked and ran like a champ and we let it idle for a while then revved it. All of this was done out of water, but we were supplying it with flusher muffs.

The whining is coming from the added fuel pump. You can hear the exhaust and what sounds like a locomotive. I'm trying to diagnose the locomotive sound.
 
There's no easy way out of this one. One way or another you'll be turning some wrenches. You can start by taking off the timing cover, remove the drive gear on the balance shaft (leave the shaft in place it'll just sit there) and retry to see if that's it. Otherwise you might have to dig much deeper...like see if it's a spun bearing. That's my extremely sketchy advice from this keyboard. You need a knowledgeable person on the scene, not us guessers.

Pop sound and burnt plastic smell...have you looked to see if an exhaust flapper went south? Although it wouldn't burn up...hmmmm...spitballing here
 
Last edited:
Watched video again. Are you sure it's not the water circulating pump on the front of the engine? It def sounds like something with failed bearings. Alternator? So hard to tell without being there
 
o2batsea said:
Watched video again. Are you sure it's not the water circulating pump on the front of the engine? It def sounds like something with failed bearings. Alternator? So hard to tell without being there
Click to expand...
I really, really, hate to say it but if I had to guess, I'd almost certainly tell you it's coming from within the block.
 
Will be removing the outdrive to see if there are any issues within. We feel like fools for only now realizing that we were running it at full up trim.
 
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