Low compression in cylinder 7
Thread Starter
Teching In
Joined: Mar 2019
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Low compression in cylinder 7 Hey guys I'm have a difficult time finding out why my ls1 is down on compression. I checked all cylinders and they were all between 200-205 except for cylinder 7. It's coming in at 65. The car at idle had just a very slight miss but once you started to throttle going down the road it was like a shutter and seemed way down on power. The valve springs, pushrods, rocker arms all look great. Ran a bore camera in and the cylinder walls look great and so does the piston. No sign of the valve touching the piston. Still need to run a leak down test but wasn't sure if anyone else had run into this before. Bad lifter? Or wiped cam lobe? Cars got prc 227 heads and ticks polluter v2 cam.
It’s time for a leak down test. 100# shop air with the radiator cap off. Start on cylinder 7 with it at tdc. This should help pinpoint the issue. With compression that low it should be easy to find. Could be a burned valve or bad seat
Thread Starter
Teching In
Joined: Mar 2019
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I never checked it with the oil cap off off but will this week once I get it out back together. It has to have crazy high crank case pressure because there was so much oil blow by my intake is coated and it's ran all the way down and rested in my bellow before my maf.
TECH Senior Member
Joined: Jun 2016
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From: Central Cal.
One thing I know- If I once found super low compression on one hole, the LS forums would not be my first thought. I would have torn that engine down as you KNOW there is something mechanically wrong. Everyone here is just guessing as we are not there looking at your engine.
11 Second Club
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If the cylinder looks Ok as you said, meaning the valves and cylinder walls have no apparent damage, then check the head gasket. It the one part that does not show damage until tou take the head off. Check the oil to see if it is milky and the radiator for oil. Good luck.
Thread Starter
Teching In
Joined: Mar 2019
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Well it ended up being broke ring lands in cylinder 7 after a really crappy tune( I know it was my own fault) but you live and you learn. Got it back together with new injectors and had it dyno tuned really happy with the number being a stalled auto with a s60 out back. 441 rwhp. Should be an awesome cruiser now!
