How do you test compression?

"personal_hygiene" wrote

Take out ALL the plugs, so the engine can spin easier, with less stress on the starter and battery.

Disconnect the coil so you won't have 50,000 volts arcing all over the place looking for a ground, possibly frying the electronics or zapping you.

Open the throttle so there's no resistance to the incoming air. Can't compress air if it can't get in.

actually, you should disconnect the EFI(some others call it ECU and maybe something else)fuse to disable the fuel injectors and the ignition system. you don't want to start a fire in the engine compartment do you?

don't remove the MAIN fuse cuz otherwise you won't be able to crank it. remove all the plugs and hold at WOT while cranking like 5 seconds. release the pressure and do this like 3 times per cylinder to get an average.

"MasterBlaster" place looking for a ground, possibly frying the electronics or zapping you.

That's a good answer. I thought you could pump the gas and fill it with gas vapour. I always thought of compression test as measuring how powerful the engine is. This seems like a leak test. Very disappointing.

"MudPuppy1976

"MudPuppy1976

any drivability problems? as long as everything is running good, i would leave well enough alone. of course, if there IS a problem, then perhaps a rebuild is in your future

Well, it is both....

If the piston rings are leaky, the engine will be low in power.

If the compression is too high, then you look at a carboning up problem.

Mike

"MudPuppy1976

what kind of car is this? i have had a few cars over 100k and never have done rebuilds. 1989 camry 270k, 88 s10 blazer 199k, 93 wrangler 149k. all had very good maintenance records, and all ran extremely well for their age and mileage. as long as you take care of them, they'll last. i don't have the camry and the blazer anymore, but i see them around now and then.

"MudPuppy1976