93 3.0L Mercruiser will crank, will not start

[Crazyko]

My 3.0l won't start.

Re: what should compression be on a 3.0L?

It sounds like it is a bit high unless the gauge is off. Do you have someone elses gauge to try? Only thing I've heard that would cause a high reading, is allot of carbon build up. Normally, not an issue on 4 strokes. Were the plugs black? How has you engine oil consumption been? I use seafoam sprayed into carb, to get rid of it on my 2 strokes.

Hello,

My 93 Mercruiser 3.0L is cranking great but will not turn over. Hasn’t been started for 8 months, replaced the starter plugs and cleaned out the carb(waiting on rebuild kit). I have spark and fuel at least getting to the carb. I checked my compression last night, keep in mind it has not been ran and it’s still pretty chilly here. 1-3 40 psi and 4 had around 60 psi... 1-3 spark plugs are brand new but covered in oily burnup. Are you saying sea foam could stop that extra oil from getting in there?

 

[Crazyko]

Hello,

My 93 Mercruiser 3.0L is cranking great but will not turn over. Hasn’t been started for 8 months, replaced the starter plugs and cleaned out the carb(waiting on rebuild kit). I have spark and fuel at least getting to the carb. I checked my compression last night, keep in mind it has not been ran and it’s still pretty chilly here. 1-3 40 psi and 4 had around 60 psi... I just replaced the plugs and when I pulled them out 1-3 spark plugs are covered in oily buildup. 4 is relatively clean. If I pour a little gas in the carb while turning it over it will back fire a bit through the carb. Another forum I read said sea foam might fix the oily buildup issue and I’d like to get some opinions on if that would stop it from fully starting. The manual I have read said the firing order is 1342.

other information, I bought it from the last owner not running. Last fall the trans union was replaced and the whole engine was pulled out and put back in. I went through the plugs and distributer. I’m getting spark all the way through but inside the cap had some buildup that I cleaned thoroughly. Done my best to check all wiring, cleaned out cannon plug which was corroded on the inside, throttle does not have a safety shutoff switch. Any idea for what to check next will be welcomed!

 

[Bondo]

1-3 40 psi and 4 had around 60 psi... 1-3 spark plugs are brand new but covered in oily burnup. Are you saying sea foam could stop that extra oil from getting in there?

Ayuh,...... Sounds like you need a new motor,...... 100 psi is a rebuildable core motor,.....

A Runner needs 120 to better yet, 150 psi,.....

A leak down test might tell ya where the problem is,....

 

[TunaFish389]

Your compression needs looked at. You shouldn't be below 100 psi.

 

[Scott06]

Compression that low it won’t run. Unless you compression gauge is wayyyyy off or someone mis adjusted the valves such that they don’t close you have a dead engine.

 

[nola mike]

Double check that compression. If it's right, that's bad news. Cranking and turning over are the same thing. Presumably you mean that will crank but not start/run. Also, sounds like the part that was replaced was the engine coupler.