Low compression on all cylinders

[Sirayden]

Hi. I'm new to buicks and have an 87 GN that has 65psi on all cylinders(tested with WOT, warm engine). The engine supposedly has low miles(stock cam, .30 109 block) and it runs strong, idles smooth. Tested with an autozone loaner gauge and now with a Harbor Freight one and same readings. Any ideas? Thanks!

 

[machinegun]

Select one of the middle cylinders, squir about 2 to 3 squits of oil form and oil can into the cylinder.

Do a compression check

Proepr way to compression check: Remove all sparkplugs, hold throttle wide open. Crank to ensure the cylinder sees 3 compression strokes. Record information.

Let us know what you find

 

[Sirayden]

Ok, thanks. Also, I have a little smoke at startup but goes away when the engine warms up. No oil in intercooler pipes but oil in the intake. PCV running to a catch can. Just pulled the intake so we'll see if it's the gasket....

 

[TurboBuRick]

What do the spark plugs look like?

 

[87chrisss]

might have some worn cylinder's/ rings, or Turbo seals leaking, does the engine consume any oil? any blowby out of the breather's

 

[Chuck Leeper]

Rings on upside down???? Odd that all 6 cyls are all the same exact reading.....

 

[Sirayden]

Yeah strange that all are the same. Plugs are fairly black looking but a possibly intake gasket leaking oil into the runners might be the cause. Don't think it's the turbo seal since no oil in the intercooler pipes or on the throttle body butterfly valve. Oil is in the intake though but no oil is collecting in the catch can. Tricky trying to diagnose it when I may have other issues at the same time. Could the cam be off causing the low pressure readings? Maybe I should take off the rocker arms and try a compression test like that? Thanks for the help!

 

[Turbo Loyd]

I would make sure the cam was installed/degreed properly.

 

[Chuck Leeper]

Yeah strange that all are the same. Plugs are fairly black looking but a possibly intake gasket leaking oil into the runners might be the cause. Don't think it's the turbo seal since no oil in the intercooler pipes or on the throttle body butterfly valve. Oil is in the intake though but no oil is collecting in the catch can. Tricky trying to diagnose it when I may have other issues at the same time. Could the cam be off causing the low pressure readings? Maybe I should take off the rocker arms and try a compression test like that? Thanks for the help!

Oil in the system could add to the seal on the rings, not detract from it.
As Loyd mentioned, the cam in wrong will cause this.
You can't remove the rockers and do a compression test. That test would be a leak down test. Probably a good idea. That will take cam timing out of the mix. A hi leak rate would be:
A. Ring seal.
B. Valves.
If the test shows normal on a leak down, then it's time to pull the ft of the engine off, and check cam timing......

 

[Mike Licht]

the cam must be retarded , my guess is that is has a roller chain and the wrong mark was used
Mike

 

[bison]

the cam must be retarded , my guess is that is has a roller chain and the wrong mark was used
Mike

I've seen that before. My clue wasn't the low cranking compression though.

 

[Sirayden]

Going to do a leak down test and see what it says. Thanks.