Diagnosing low compression cylinder
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
TECH Resident
Joined: Mar 2012
Posts: 859
Likes: 402
From: Texas
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?
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
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.
Trending Topics
TECH Addict
Joined: Dec 2017
Posts: 2,180
Likes: 969
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.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo That's what a leak down test does.
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.