Thread: Inconsistent Compression Numbers?

I don't want to replace my engine if it's still healthy... I do it one minute and get 170 psi then I try it on the same cylinder right after and I only get 140psi. I've had 170 psi on 3 cylinders and then they wouldn't read that anymore only 140 across the board and then 120... It gets annoying and I don't know if it's actually the engine or simply the compression gauge? Any input?

If I had results like that doing a back to back test with the same conditions and had a 170 reading and a 140 reading, I would not believe the gauge.

there's probably a sealing effect going on with fuel on the rings, causing you to get different numbers. Doing check after check repeatedly with injectors still firing will definitely skew your numbers.

There is a proper way to doing a compression test. Vehicle at operating temp, remove ALL spark plugs, crank 6 times at wide open throttle. You have those parameters?

You also have to unhook the fuel injectors, OR remove the fuse to the fuel pump with the car still running first.

You forgot about the fuel but yes all of those were done.. When I remove all the spark plugs it cranks really really slow like 1/4th regular speed and with all bit one removed it cranks fast but the numbers are still inconsistent no matter how I do it

Yep exactly.. Till it shuts itself off.. You dont want to crank your engine up with a puddle of fuel in the cylinders lol I know I'm doing the test correctly.

This makes me wonder if you don't have a voltage/starter issue somewhere...

Just for the record, I wasn't doubting you, just adding what was left out of the proper steps previously mentioned.

Put like a teaspoon of oil in each cylinder when you do the test and see if it helps the numbers, if so you probably have some ring issues going on. Also get a battery charger on there while your doing it. Your voltage will mess with your results also.