Poopy

I did a compression test on my Evolution 8 just for the hell of it, and got some strange numbers:

145-180-155-182 This was on 2 different gauges as well, like 3 times per gauge too. Car was fully warm, and a couple when the car cooled off. I actually got slightly better numbers with car cold LOL.

Car is stock with 125K miles, does not burn a drop of oil, and timing is lined up. Did a leak down test with a cheap gauge, so I don't really trust it and got about 15-20% leakdown on the 2 low cylinders. I could hear air escaping and couldn't pinpoint the location, I think possibly exhaust valves. I did notice my timing belt seemed a bit loose when checking my timing marks. Could the slack in a loose timing belt effect compression numbers by allowing the valves to not fully seal at TDC? But when the car is running it tightens up the belt which evens out the compression? I am just confused on how a car could run so well with such a large variance between cylinders. Not to mention what the hell happened to a stock car? Why do I have higher than spec on the 2 good cylinders? Isn't spec 178 PSI from the factory? I would expect even if the car was babied its entire life to lose some compression. I know deposits can build up, but pistons looked clean on all cylinders...could even read the part numbers on top. Spark plugs all looked the same as well.

The car idles well(some very slight vibration in steering wheel, just enough to let you know the engine is on) and pulls nice considering it is 100% stock.

I'm not in the mood to pull the head after just doing the clutch......

kaj

iTrader: (60)

first thing to do is pinpoint exactly where you are hearing the air. that will tell you where you problem is. you said it sounded like it was form the exh valves.. does this mean you heard air exiting the exhaust?

Poopy

I just know it wasn't coming from anywhere else. Would have to pull the manifold to tell for sure.

kaj

iTrader: (60)

you do not need to remove anything for a leakdown test other than the UICP from the TB and the dipstick. you may also need to plug a vacuum line or two. i can't remember off the top of my head.
"not coming from anywhere else" isn't enough to base a diagnosis. unless you like spending loss of time and money trying to fix the problem, that is. find the source of the compression lost first.

Poopy

No ****. That is what I meant by not coming from anywhere else. Meaning I checked everything including radiator, crank case, intake, adjacent cylinders, etc. The only thing I couldn't verify was the exhaust. Hence my assumption since everything else did not have any leaks led me to believe it is the exhaust valves. I am not going to be able to hear/feel such a minimal amount of air out of the rear exhaust for obvious reasons. I suppose I could put a condom on the exhaust to see if it fills up to check the exhaust valves. Looking for advice and possibilities on what could have caused this on a stock car, or if anyone might have any theories of the compression number variance and the fact that the car runs pretty much perfect. Please don't bother posting in here if you are going to scold me, thanks.

kaj

iTrader: (60)

i'm just trying to help. if you want to tear your car apart with the assumption the exhaust valves are leaking, feel free.

or, you can pressurize the tester and go to the back of the car and listen.

there was no scolding in any of my posts.

Poopy

I doubt I am going to be able to hear if they are leaking through the stock exhaust. But yes, I did go to the rear of the car and tried to listen and couldn't hear anything. Considering the sound has to bypass the turbo, cat, and muffler...I'm not going to hear it if the ex valves are leaking.

Lets just say for fun that I confirmed the ex valves are leaking. Could a loose timing belt that allows the cams to shift slighty cause the valves to leak during a compression/leakdown?

kaj

iTrader: (60)

you would hear the air. a distinctive "hiss" as opposed to hearing absolutely nothing if they weren't leaking. this is just my experience. yours may differ, i suppose.
yes. if the timing on the cam is off enough, you could DEFINITELY have some valves open. if valves are the confirmed culprit, i'd be all that timing belt. it may just be that simple.



if i weren't at work, i'd check to see if those to cylinders were next to open in the timing cycle. very suspicious that two, non-adjoining cylinders read low.