Diagnosing low compression cylinder
05-24-2019, 09:01 PM
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Diagnosing low compression cylinder Looking for some feedback. I have a lq9 with roughly 180psi in all cylinders except for cylinder #8 with 95psi cranking pressure.
Inconsistant leak down test results so far. Thinking I have a lifter or valve issue (Valve to left in video). Please see youtube Video.
Thanks
Inconsistant leak down test results so far. Thinking I have a lifter or valve issue (Valve to left in video). Please see youtube Video.
Thanks
05-24-2019, 10:18 PM
#2
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If that is indeed cylinder number 8, my recommendation is to loosen the rocker arms, then pressurize the cylinder. If it holds pressure well, then you're going to have to take the cylinder head off and find out what is wrong.
I hope that helps.
EDIT: Did you do this test with all of the spark plugs out?
I hope that helps.
EDIT: Did you do this test with all of the spark plugs out?
05-24-2019, 10:50 PM
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If that is indeed cylinder number 8, my recommendation is to loosen the rocker arms, then pressurize the cylinder. If it holds pressure well, then you're going to have to take the cylinder head off and find out what is wrong.
I hope that helps.
EDIT: Did you do this test with all of the spark plugs out?
I hope that helps.
EDIT: Did you do this test with all of the spark plugs out?
Good Idea, I will try again after loosening the rocker arms, just to avoid and possible pressure on valve. My hope is that its not a bent rod.
Thanks
05-24-2019, 10:54 PM
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This was done not cold but not operating temp (roughly 140 coolant temp). I didn't squirt oil into the cylinder either. I had about 4 percent leak down in that cylinder, which lead me to scratch my head after only getting 95psi compression reading.
05-24-2019, 11:35 PM
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If compression comes up with oil squirt its rings. If not, its a valve or head gasket.
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05-25-2019, 04:30 PM
#8
Try an air fitting and compressed air. Just see where the air goes.
It will either leak into the crankcase (rings), intake (int valve), or exhaust (exh valve). Any other possibilities are pretty remote.
My money would be on a valve, but you never know until you check.
It will either leak into the crankcase (rings), intake (int valve), or exhaust (exh valve). Any other possibilities are pretty remote.
My money would be on a valve, but you never know until you check.
06-03-2019, 07:03 AM
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It was a bent exhuast valve, you can see in the video. The one on the left ticking and returning slowly to its seat. Problem was it would return to the seat and seal....and give me good leak down numbers but when cranking would be low compression numbers. Thanks the help guys, new heads already installed with upgrades.