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1995 150hp Mercury missing at wot.

S

skullbone30

New member
I have a 1995 mercury that starts missing and will bog down to almost a stop after running wot for a couple miles. It has been in 2 shops and both diagnosed it to be not firing on number 5 cylinder. "First guy replaced power pack with used one. When I picked it up ran the same. Took to another shop they replaced power pack with new one and fuel pump diaphragm. When I picked up ran the same(after they lake tested). Returned it they tested more and changed plugs. I picked up tried it ran the same. returned it. After a week I was told to come get it they couldn't fix it till it got worse. I myself have changed plugs, fuel filter, fuel line, bulb, voltage regulators, number 5 coil, drained gas and put new in, and run quickclean in it. Another shop will look at it in 3 weeks put after talking to them on the phone they don't sound promising. Any ideas or things I can test would be appreciated. I'm pretty good mechanic on cars and thing but don't know much about outboards. Thanks in advance.
 
Not firing on #5 does this mean no spark or nothing changes when you pull the lead off #5 plug ?----------Have you inspected carburetors ? --Inspected reed valves -Have you done a compression test ?-----Water pump in good shape ?-Does spark jump a gap of 7/16" on all 6 leads?
 
Yes no spark on number 5 is what each shop said they found when they diagnosed it. I actually saw the first guy check it before I left the boat. Yes compression is good on all cylinders. It is an efi engine. and just put new water pump in and runs about 18 psi on gauge at wot if engine isn't trimmed all they way up.
 
It is an efi engine.
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With it shutting down its a electrical or fuel issue. Is it overcharging? If so this can overheat fuel pump and ecu causing engine shutdown. Once it dies will it restart and run or just bog? Is fuel pump loud when running? Check the fuse holder also so as they can cause problem with high resistance connections. Also a bad bias circuit will cause a single cylinder to drop and the pack thats not firing is good, its the opposite pack that is working that is actually bad.
 
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