Got These Engine Compression Test Results....

[04SS6.0]

So i did a dry and wet engine compression test on a cold engine today. I have a 2004 Silverado SS 6.0 with 370,000km on it

Cylinder 1:  Dry 120 PSI Wet 140 PSI                

Cylinder 2:  Dry 121 PSI Wet 139 PSI

Cylinder 3:  Dry 119 PSI Wet 140 PSI

Cylinder 4:  Dry 120 PSI Wet 138 PSI

Cylinder 5:  Dry 121 PSI Wet 138 PSI

Cylinder 6:  Dry 121 PSI Wet 145 PSI

Cylinder 7:  Dry 120 PSI Wet 140 PSI

Cylinder 8:  Dry 120 PSI Wet 145 PSI

 

Should i be worried? i remember doing an engine compression test about 1-1.5 years ago, all the cylinders were in the high 160s PSI and low 170s PSI, how such a big change in short amount of time and how come all the cylinders are so equal. Could it be a defective compression gauge ?  Would this cause a P0300 engine code? 

 

[Jglew82]

Try another gauge if you like, but those readings are pretty well in spec, especially for that high of mileage. Book says anything below 100 psi is an issue. Normal wear of the rings in this case, I'd say. Are you getting a P0300?

[SierraHD17]

Yeah those are low for an LQ9... should be 170 to 180. 370000 kms is high enough though so who knows. The big thing is though that the numbers are equal which is a good sign.  Make sure the throttle was wide open during the test and you could always test a different gauge.  

 

I would more look at needing a CASE relearn to fix the random misfire code.  It usually cures that because it resyncs the crank and cam sensors which get out of sync with play in the timing chain.

[04SS6.0]

15 hours ago, Jglew82 said:

Try another gauge if you like, but those readings are pretty well in spec, especially for that high of mileage. Book says anything below 100 psi is an issue. Normal wear of the rings in this case, I'd say. Are you getting a P0300?

Yeah the only thing that worries me is maybe a year ago i did a compression test and they were all 165psi-170psi. Only major thing i did was delete my mufflers & put in straight pipes because i like the sound, but that wouldn't wreck the engine like that would itÉ 

 

Had a P0300 for the life of me couldn't figure it out even took it to a mechanic and they couldn't. I put a new intake manifold gasket prior to the mechanic Fel-Pro brand.  I did a smoke test on my intake had leaks from 2 injector O rings passenger PCV line, Oil fill tube, & where the cold air intake bolts to the manifold, terrible design from AFE. Got all those issues sorted and have no smoke that i can see. Have another intake manifold gasket on hand by Mahle in case that Fel-Pro wasnt sealing but i did not see smoke after those fixes.

 

I also ordered 2 different ODB devices one Blue Driver and tried to read Engine misfire count in Mode $6 but GM didnt start doing that till 08 in vehicles returned it. Bought another ODB device, touch screen Launch one they said i would be able to read engine misfire count in Live Data in Mode $1. Go to mode 1 and its not there, Their engineer is away till the 8th so i dont have an answer. Will probably return it. I just want a scanner that will tell me my cylinder misfire counts. 

 

The code has come back but i feel like i can still feel misfires even tho no codes or pending codes have come up yet. 

[04SS6.0]

11 hours ago, SierraHD17 said:

Yeah those are low for an LQ9... should be 170 to 180. 370000 kms is high enough though so who knows. The big thing is though that the numbers are equal which is a good sign.  Make sure the throttle was wide open during the test and you could always test a different gauge.  

 

I would more look at needing a CASE relearn to fix the random misfire code.  It usually cures that because it resyncs the crank and cam sensors which get out of sync with play in the timing chain.

Yeah i am happy they are equal across the board. A year ago i have 165-170 psi in all cylinders which worries me. Only thing i did was delete my mufflers.

 

Would a bad timing chain cause bad compression? Yeah i think they did a crank position sensor relearn at the mechanics about a month ago. If that is the same as the CASE relearn you're talking about