Compression Help

[CMIDD]

Alright. Wanting to run a compression test on my boat engine. Is it pretty much the same as running one on a car engine? I am clueless here...

[Jbyrd]

Alright. Wanting to run a compression test on my boat engine. Is it pretty much the same as running one on a car engine? I am clueless here...

Pretty simple, Start by pulling your kill switch. Then remove a spark plug starting at the top or bottom doesn't matter. Using the screw in tester, after removing the plug insert the tester and crank your motor. After checking each one replace plug wire before moving on to the next so you don't get your wires crossed. depending on type of motor they should test within 5 lbs of each other. If one is higher or lower than the rest it maybe a potential problem.

[MarkW]

I always remove all spark plugs when I do a compression test. But, for sure make sure you pull your kill switch.

[DaveR]

I also read recently to keep your throttle all the way open while cranking, Not sure if this is still required for new EFI's, but I did it anyway.

[CMIDD]

Ok. I think there is something wrong with my compression gauge. Tested today, gauge read between 35-40psi on all six cylinders. That seems awfully low. The engine starts and runs great. I think I will try a different gauge tomorrow. Seems to me that if the compression were that low, the engine would not even fire.

[DaveR]

make sure you let it go thru 4 or 5 compression cycles to build up pressure

hard to watch and crank by yourself sometimes.

[CMIDD]

I was wondering how many cycles to go through. I am use to working on cars, and was not sure if the two cycle was any different. Would it start and run with 40 psi????

[otis44]

I don't know if one would run at 40psi or not, but i'd bet your gauge is bad or something else is going on. I've also read that a warm engine will read a little better (not much but a little) than a cold engine.

[DaveR]

You can borrow my guage if you are anywhere near louisville or bullitt co