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low compression on all cylinders...

18K views 45 replies 12 participants last post by  pitchedblack04  
#1 ·
Ok guys, well to start things off i just recently got finished installing a custom turbo set up and got it tuned last weekend with tom. Well i pulled the plugs to change them and noticed some oil on the bottom of cyl 1 plug. SO i thought well i wanna do a compression test just to see whats up. Well im gettin 90 psi across the board. Could this be a timing issue as to why im low compression on all 4? And does is sound like valve seals if ive got oil on that plug? The VC is not leaking. Any help would be greatly appreciated.
 
#4 ·
it could be a number of things. ive seen just enough water sucked up to bend all the rods but not break them, but i dont know what the odds are that they would all bend the same amount. a timing issue or head gasket. the rings not sealing would make different numbers not all the same.
 
#8 ·
Even with the VCT you should be around 135. I had one here this past summer that had the same issues... ~90 on all 4 cyls... it was NA and wouldnt pull itself out of bed.
 
#10 ·
its probably not the rings. the odds of all your rings having the same amount of blow by to give you 90psi across the board is slim. look at anything that would affect all cylinders the same.
 
#12 ·
It's cam timing. It's the only thing that could create even numbers that are off . . . but we have to ask if the engine is stock or was the compression lowered for the turbo setup?

If it's raw oil on the plug it's going to be a VC leak. A valve stem seal would leave burnt oil deposits on the plug and never raw oil.
 
#17 ·
^^^ You need a set of feeler gauges, specs, a new valve cover (maybe not right now), and then you rotate the cam until you're at TDC for that cylinder, then put the feeler between the cam lobe and the bucket. You want the feeler gauge to be touching both sides, but not shoved tightly in- you should be able to feel resistance if you tilt it ever so slightly up or down, and if you let go of the gauge it should not tilt on it's own. You may have to combine gauges to get the correct size.

If you have a Haynes manual, it should describe the process with pictures in the General Engine Overhaul section.
 
#19 ·
yeah, VC gasket, sorry

It sounds like you need one of those in the first place where you have oil on the outside of a plug, usually it's the gasket that seals the spark plug tubes that is bad, so it might not leak on the outside.
 
#20 ·
I doubt its anything to do with the cams. During the compression stroke both the intake and exhaust valves are supposed to be closed and shouldn't affect the compression of the motor. What would is severely burnt valves (unlikely across all cylinders...) or worn rings (more likely.)

Before tearing into things, I would throw a leakdown tester on it first to see exactly where the compression is being lost. You will be able to feel whether is exiting through some bad valves (through the intake tract, or exhaust pipes) or out past the rings (you will feel air moving out of the oil fill hole).
 
#29 ·
Its going to be the rings, if the cam timing was off you would have definitly noticed it before now AND you would have a CEL and code for VCT over advance.

A leaking valve cover doesnt mean shit when it comes to compression and if it was a valve it wouldnt effect all 4 cylinders.

Rings can be fine when NA and can go straight to hell after you add boost.


Go advance your exhaust cam 5* and take a compression reading. Same thing at 0* and at 5* retarded. You'll see the number changes quite a bit and evenly across all cylinders.
The static compression hinges on how well that cylinder fills with air. Too much overlap and you will loose compression.
If the timing has never been dead on you'd never know the difference.

digging

This could be an explanation for this --> http://www.focusfanatics.com/forum/showthread.php?t=207262
 
#24 ·
Its going to be the rings, if the cam timing was off you would have definitly noticed it before now AND you would have a CEL and code for VCT over advance.

A leaking valve cover doesnt mean shit when it comes to compression and if it was a valve it wouldnt effect all 4 cylinders.

Rings can be fine when NA and can go straight to hell after you add boost.
 
#28 ·
Of course I was sheesh, and I just told you how to check valve lash because you asked. You already had the answer to what the most likely cause is of your engine not running. You're taking a chance by putting boost to an engine with over 50k miles on it- sometimes you win, sometimes you lose.

I'd take the earlier advice to do a leak down test to find where the compression is escaping to in order to verify what's going on, but I'll bet you'll be working with a ridge reamer, a set of rings, and head gasket kit fairly soon. Might as well change the timing belt and tensioner as well while you're in there.
 
#34 ·
Yea me too i just gotta get time to check.

How was the engine running before installing the turbo? If ok, did you do anything else to the engine? Did you warm the engine up? Block the throttle open? Turbo only should make no difference......
Engine ran fine. I didnt hear any weird noises and it didnt feel like anything was wrong. And yes car was warm and TB was wide open.


Sure it can, if the rings were weak then the added boost from the turbo could easily be enough to cause blow by.

If he didnt buy the car new then none of us can say how good/bad it was taken care of prior to him getting it.... sure it may only have 60k miles on it but they could have been extremely hard miles.
The only thing that gets me about the rings is shouldnt i see a difference once i put the oil in the cyl if it were the rings? And the previous owner was an older guy probably around 45 had money this was just a toy he used when he went biking. He had a roof rack on it. He bought an xcal 1 from sct and he loaded the tune on the car but then took it off because he thought he might not pass an emission test. He seemed like a very good guy and he deff took care of his house and the other cars he had. But like you said i/we really dont know.