Low Compression! Piston Rings?
Posted 15 April 2018 - 05:52 PM
Posted 15 April 2018 - 06:03 PM
Posted 15 April 2018 - 06:05 PM
you should always check compression with the throttle open
Posted 15 April 2018 - 06:14 PM
Unfortunatly that is what another engine I worked on was like when the ringland cracked.
As above it could be the valves, so that is worth checking. The fact that the oil brings the pressure up though suggests that probably the rings are leaking.
Agree with the throttle open comment too, try it again with it open.
Edited by james4563, 15 April 2018 - 06:15 PM.
Posted 15 April 2018 - 06:18 PM
Posted 15 April 2018 - 06:21 PM
Maybe throttle open so there is no vacuum before compression?
plus engine usually cranks faster and thus a better reading
Posted 15 April 2018 - 06:33 PM
Posted 15 April 2018 - 06:34 PM
Edited by Vx220-blue, 15 April 2018 - 06:34 PM.
Posted 15 April 2018 - 08:15 PM
Posted 15 April 2018 - 08:54 PM
Edited by OL11TAL, 15 April 2018 - 08:55 PM.
Posted 15 April 2018 - 08:59 PM
Edited by Vx220-blue, 15 April 2018 - 09:01 PM.
Posted 15 April 2018 - 09:54 PM
Posted 16 April 2018 - 07:11 AM
1 - 150psi 2 - 150psi 3 - 70psi 4 - 150psi
I'm sorry to say that's a vast difference, either that cylinder's rings are broken/worn/bent or has an uneven/washed bore. I doubt its valve seat leak as that wouldn't make such a marked difference unless the valve stem has bent due to spring failure.
Who mapped it?
Edited by Nev, 16 April 2018 - 07:16 AM.
Posted 16 April 2018 - 07:32 AM
a quick google says;
Normally this type of failure affects the exhaust valves only, but it can also damage the intake valves. A burnt valve will cause issues with your vehicle's performance and fuel consumption. Rough idle, reduced power, backfiring, and misfire are all symptoms of valve burn
Posted 16 April 2018 - 07:51 AM
I've never heard of a Z20LET burning it's valve seats TBH, but I suppose it's possible. I have however seen umpteen melted pistons and quite a few cracked rings though. If you go on the Z20LET lovers Farcebook forum there must be a new picture of a melted piston every week or so (here is one from 2 days ago: https://www.facebook...3&theater&ifg=1 ).
I would imagine that the melting point of the pistons (which are only some sort of cast duraluminium) will be a good deal lower than the steel valve seats. Anywho, the resolution is engine out, take the head off and have a look, lots of work/expense I'm afraid.
If you fix/replace your engine, you should also review your map, IATs and existing sensors (so it doesn't happen to the new engine). Usually the cause is "over-optimistic" mapping, hence why I asked who mapped your car.
GL (and let us know what it was if you find out please).
Edited by Nev, 16 April 2018 - 08:14 AM.
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