mercruiser 3.0 with 90 psi compression on all cyl.,

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Stubby234

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Jun 13, 2012
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90 psi on each cylinder, is that low enough to make engine hard to start ,not idle and seem like it has not very much power
 
Oshkosh1

Oshkosh1

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Jun 8, 2009
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Re: mercruiser 3.0 with 90 psi compression on all cyl.,

Thats pretty low...If those numbers were taken from a warm engine, it's awfully tired and will definately have issues. I believe it should be running 140-150psi or so.
 
F

fishrdan

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Jan 25, 2008
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Re: mercruiser 3.0 with 90 psi compression on all cyl.,

90PSI is pretty bad and could cause these issues you mentioned.

But, did you do the compression test correctly? Warm up engine, battery fully charged, remove plugs, throttle wide open, test each cylinder by cranking 3-4 revolutions?
 
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Stubby234

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Re: mercruiser 3.0 with 90 psi compression on all cyl.,

engine was cold, took one plug out and tested one by one,throttle wide open and cranked 4 times
 
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jeepster625

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May 1, 2016
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Ok I dont know if im supposed to post on here or not but I cant figure out how to start a new thread.

So I just purchased a 1979 marquis stingray with a 3.0 mercruiser and I also have 90 lbs in each cylinder. i tested it cold because I cant get it to run. Ive got it to backfire a few times but I cant get it to run. I also have a "boat" load of other questions to help me get this boat back to its former glory. Any help is greatly appreciated.
 
A

airshot

Rear Admiral
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Jul 22, 2008
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4,329
Yep....gotta agree with Bondo he is most always right on with his reasons. I know my 3.0 just got a head job over the winter, burned thru a head gasket between #2-3 and dropped comp to 95 in #2 and 110 in #3, engine became hard to start and did not want to idle and kept fouling plugs in 2&3. In my case cylinders looked perfect with no ridge and no grooves so I just had the head redone with valves ground, new springs, head flattened and reassembled. In your case with 90# on all cylinders....rebuild is in order...she won't run with 90# .
 
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