Compression ?

stocker 89

Registered User
what should should psi or kPa be when doing a compression test on a stock 3.8 supercharged motor. My chilton does not give an answer it just says that your lowest cylinder should be within 75% of your highest cylinder.
 
Got a 95 with one cylinder bad. It started at 65 now down to 55 psi. The others on this car and the 89 & 91 are (?125/135?) up to 150+. The car with one cyl low idles a little rough and power is down. Look for balance code as well.
 
I got 158psi every cylinder after 3 revs with throttle wide open and engine warm. My 94 motor has about 30K on it.
 
OK! got the compression test done.

CYL 1 150
CYL 2 150
CYL 3 150
CYL 4 143
CYL 5 120
CYL 6 145 PSI

Car is stock 3.8 SC 1989 has a little under a 100,000 miles on it. Is this good bad or what? what do you think is the problem on CYL 5. Are the rings worn on wrong or broke or is a valve not seating ?
 
You can put a small amount of oil in the 5 cyl.A table spoon.

Then do a compression again on the 5 cyl. If the compression
comes up, this is a sign that you have bad rings.The oil will seal
the rings making the compression come back.

If the oil in the 5 cylinder will not bring the compression back up.
This may mean you have a valve leaking.

Use a heavy wt. oil.

You can also use compressed air in the sparkplug hole.
IF you hear air coming out the intake (throttle body), or exhaust,(tail pipe)
you have a bad valve.

If air comes out the oil fill hole or PCV valve ,the rings are bad.

randy
 
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Yeah, I will try putting some OIL in 5. Notice the drivers side head is the one with different readings. This is the side without the EGR and NO cats in it. I think I might have some burnt valves. Should I keep on driving it or should I have that head redone.
 
I would not think it would hurt to drive it.As long as its not
a head gasket leaking.

Make sure you don't have oil in the cooling system,or anti freeze
in the oil.

good luck randy
 
HEY , JASON belive me when I tell you I know what driving with bad head gaskets is like. I know this for sure it takes around a hour longer to go 50 miles.
 
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