Compression testing

[Ponyryd]

So when I do a compression test I usually do it on my own, I pull the fuel pump relay first, then the starter relay so I can actuate the starter from under the hood with a jumper wire, I connect my gauge and do 3 cycles, that number is what I use.
Now the other day another guy was doing a compression test (as stated in another thread, we got tons of cars in that injested water from the flood last week) and he was cranking basically until the gauge stopped climbing......so now I wonder, have I been doing it wrong all these years? Not that it matters much since it's usually just for comparison to find a weak cylinder, but I'm curious. Whaddya you guys do?

[ZR]

Roll for three pumps on the gauge just as you've always been doing it.

[ZR]

Injested water, I'd dump oil n filter, pull plugs, shot of oil down the cyls then roll over till all looked clear. Plugs back in, fire up and see how it sounds, likely take a few minutes till it settles.

[98 Snake]

I crank until the needle stops, usually around 5 rotations

[Ponyryd]

Injested water, I'd dump oil n filter, pull plugs, shot of oil down the cyls then roll over till all looked clear. Plugs back in, fire up and see how it sounds, likely take a few minutes till it settles.

Water injestion job isn't mine, in the next bay, I went over to help with the diag on it, #5 piston is 1/4" lower at tech than the rest, so somewhat bent rod, car runs quiet but has a misfire, likely going to scrap, it's a 2.7L.

[jpstang]

Hey guys looking to do a compression test on mine as well. Read that you should warm up the vehicle for more acurate reading. Is this true?

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[ZR]

Many will disagree but it's my feeling a cold test gives you a better picture into an engines real condition. No downside to doing cold them comparing to hot though.

[Ponyryd]

^Agreed, although it sucks using the tester on a hot engine if you have any feeling in your hands.
FWIW I never do a compression test on a good running engine, to me it’s pretty pointless if everything else is working fine. Good idea if you suspect a problem, or if you’re selling the engine though.