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Compression Test

RedGrandPrix

RedGrandPrix

New member
I had the car compression tested today:

1999 Pontiac Grand Prix GTP 109,000 miles

#1 130 psi
#2 150 psi
#3 130 psi
#4 145 psi
#5 140 psi
#6 150 psi

Are these numbers good or bad?
 


As long as they all around around 10-20psi within each other it is supposed to be in great running shape IMO. Seafoam it...then test it again and see if it becomes even more consistant of a psi.
 
well, 10% of 150 is 15...so that would give you a lee-way of 135-150, so you are like what? 2% ish difference on 2 pistons...like I said, seafoam it and it should all be good to go :D
 


You don't mention if this is with the throttle blocked open, all plugs out and whether you added a little oil for the wet check as well.

There are sometimes many factors that can affect a compression test. Overall your results look good though. Maybe retest those lower cylinders and see if you get a slightly different number.
 
BillBoost37 said:
You don't mention if this is with the throttle blocked open, all plugs out and whether you added a little oil for the wet check as well.

There are sometimes many factors that can affect a compression test. Overall your results look good though. Maybe retest those lower cylinders and see if you get a slightly different number.
Click to expand...



Some good points Bill.
 
yes those are some good points............what is the proper procedure for doing a compression test? Or is there a thread out there already that I missed?
 


right.......it is one plug at a time......but are the other plugs all in? anything special done with the intake region? Etc......????
 
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