Compression Test Question.

I always do compression test cold. My thought is this is most likely to give the worst numbers as everything isn't good and lubricated. If you get great numbers you can feel good. I actually just pulled that thought from where the sun doesn't shine, but I do test them cold.

 

Usually you do the test while the engine is at operating temperature. If the last time the plugs were installed with a little anti-seize they should come out easily. If not, with a cold engine, pull out the plugs, give the threads a little anti-seize and reinstall. Warm the engine up, then pull them and test. Keep a battery charger hooked up to keep up the voltage, crank each cylinder the same number of times, I usually do 5 or 6 "puffs".

 

There's probably multiple right answers here. Compression tests can be done cold or hot.

I think the reco regarding plug removal on a hot engine is actually a recommendation not to put a cold plug into a hot head - I seem to recall that being the bigger concern.

Best way to go here is likely to be to warm up the engine somewhat - not necessarily up to full operating temp - and then perform the test. Sounds like you know what you're doing (remove fuel pump fuse, test with throttles open, etc.) anyway. Good luck on the #'s!

 

there is a new way of doing compression checking ussing a pressure transducer and a labscope with this method i can tell valve timing problems being able to tell if a timing belt is off a tooth or not preety cool huh saves me tons of time and ive come in and diagnosed cars for other shops with only pulling out a spark plug if your interested the guy that dreamed up the idea is out of Albequerque NM USA his names Bernie Thompson and his company ATS stands for automotive test solutions www.automotivetestsolutions.com hands down the guy makes some of the best tools and no hes not paying me

 

Also pull the plug to the coil packs so as not to cycle the ignition coils with the leads disconnected. the DIS isn't happy running with out a grounded discharge. risk of high voltage shock as well.

 

modern EFI systems also have a 'clear flood' setting, WOT @ crank will shut off the injectors. on my daily drivers that's how I've done the compression testing. I still prefer the leak down for an accurate picture of losses from rings and seats.

 

That is slick! It's one of those, now why didn't I think of that! it's almost to simple for the newer cam signaled engines. for the older ones an optical pickup on the cam would work for diagnostic input.

 

Hey i saw in the other chat that you have an ST05 how is it? What are its strengths and weaknesses. Hows it working on the newer cars. I own so many scan tools and have paid for some real crap ones that promised the world before id hate to buy one of thease one day and feel ripped off that it doesnt do enough of what i need it to.