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Low Compression In One Cylinder? Need Help

wsln33

By wsln33,
in Engines & Forced Induction

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wsln33 Collaborator

wsln33

Posted
Posted

Hi guys,

Got my car tuned the other day, it is a 26/30 and made over 450rwkw on 18psi pump through an auto. Started breathing heavily upon taking the car off the dyno I am told. It is cylinder two that is 40psi, all others are very close to 120psi. Put some oil in the bore and it went up to 65psi. It has argo rods and cp pistons and rings.

1) what is the problem? Rings gone bye bye?

2) Why did this happen?

3) Is this common or something to expect?

4) how much to fix if engine is taken to engine builder?

Thanks in advance

luvpsi Mentor

luvpsi

Posted
Posted
Hi guys,

Got my car tuned the other day, it is a 26/30 and made over 450rwkw on 18psi pump through an auto. Started breathing heavily upon taking the car off the dyno I am told. It is cylinder two that is 40psi, all others are very close to 120psi. Put some oil in the bore and it went up to 65psi. It has argo rods and cp pistons and rings.

1) what is the problem? Rings gone bye bye?

2) Why did this happen?

3) Is this common or something to expect?

4) how much to fix if engine is taken to engine builder?

Thanks in advance

id say it could be a number of thngs. it could simply be the head gasket has cracked around that cylinder or your rings have gone bye bye or many other things. i would say if its rings its a ring change depending on the bore itself. correct me if im wrong guys

MrStabby Grand Master

MrStabby

Posted
Posted
if it's your rings the I've been told the comp would come back up more than that, almost back to normal. Leak down test time for diagnoses.

Yep - to elaborate, the oil makes up the piston to cylinder clearance, like a ring would, so;

- if the compression comes back, your rings are stuffed and top end is good

- if it doesn't come back its top end, ie valve/head gasket/cracked head... OR both top end and rings....

  • 2 weeks later...
marksuxass Collaborator

marksuxass

Posted
Posted
Hi guys,

Got my car tuned the other day, it is a 26/30 and made over 450rwkw on 18psi pump through an auto. Started breathing heavily upon taking the car off the dyno I am told. It is cylinder two that is 40psi, all others are very close to 120psi. Put some oil in the bore and it went up to 65psi. It has argo rods and cp pistons and rings.

1) what is the problem? Rings gone bye bye?

2) Why did this happen?

3) Is this common or something to expect?

4) how much to fix if engine is taken to engine builder?

Thanks in advance

Had the same thing happen on my rb26, number 2 had about 25 psi, and the rest around 130 psi. Have stripped the motor down to find that number 2 piston was melted around the ring land area :P

marksuxass Collaborator

marksuxass

Posted
Posted
^ hope you use another tuner once its rebuilt.

rarely hear of a single piston melting on a proper tune.

Hadnt had a tune, stock engine stock turbos stock ecu, but with an injector with alot of crap in it. *sigh*

Rolls Grand Master

Rolls

Posted
Posted (edited)
Hadnt had a tune, stock engine stock turbos stock ecu, but with an injector with alot of crap in it. *sigh*

there is your problem, one lean injector probably = a hole in your piston if comp is that bad with oil in it. A decent tuner should have picked up the detonation though and needing more fuel than normal to compensate for 1 cylinder barely firing.

I'd be asking them what knock detection equipment they use and if they say none you ask for nothing less than a refund.

Edited by Rolls
marksuxass Collaborator

marksuxass

Posted
Posted
there is your problem, one lean injector probably = a hole in your piston if comp is that bad with oil in it. A decent tuner should have picked up the detonation though and needing more fuel than normal to compensate for 1 cylinder barely firing.

I'd be asking them what knock detection equipment they use and if they say none you ask for nothing less than a refund.

haha i know that was my problem, thats why it only leaned out on 1 cylinder. As for the tune as stated before it never had one, so i only have myself to blame for it :P

Rolls Grand Master

Rolls

Posted
Posted
haha i know that was my problem, thats why it only leaned out on 1 cylinder. As for the tune as stated before it never had one, so i only have myself to blame for it :P

oh right I got the impression it happened on the dyno, you said it happened after tuning, so it was happening before you took it there, why would you get it tuned if it was pushing loads of oil into the catch can?

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