mediocre compression on 5 cyclinders (90,90,90,90,90,120) fluctuating idle (IACV?) too much pressure pushing out dipstick and causing oil to spray in engine bay, white/blue smoke under boost.
Engine starts great, drives good, really good boost (17psi) but those problems make me really wonder wtf is going on.... if its crankcase issue, blown piston ring why would it drive so good? temperature is fine and I just cleaned the PCV valves...
suggestions? x_____x
piston rings shot?????
-
lexcrob
- Posts: 527
- Joined: Mon Sep 22, 2008 7:38 pm
- Car: I get a different ride faster than I could update this.
- Location: Clarksville, TN
Re: piston rings shot?????
Pull plugs see if any have oil on them.
Likely the dipstick issue is caused by boost pressure going into the crankcase. Try venting your crankcase breather hoses to atmosphere.
Do a leak down test.
Some situations your gonna need a good reliable gauge if its a small "leak down".
Sometimes ill just chuck shop air right into a cylinder in question and listen regulated shop air at 105psi has a certain sound.
If you see your dipstick go flying then id say yank the motor shes gone.
Beyond that you could lower the boost see if it changes anything.
Blue smoke under boost is normally gonna be the turbo or broken pistons.
Your compression test results dont really tell you anything id omit those numbers only that they were EVEN is what you'd take away.
Likely the dipstick issue is caused by boost pressure going into the crankcase. Try venting your crankcase breather hoses to atmosphere.
Do a leak down test.
Some situations your gonna need a good reliable gauge if its a small "leak down".
Sometimes ill just chuck shop air right into a cylinder in question and listen regulated shop air at 105psi has a certain sound.
If you see your dipstick go flying then id say yank the motor shes gone.
Beyond that you could lower the boost see if it changes anything.
Blue smoke under boost is normally gonna be the turbo or broken pistons.
Your compression test results dont really tell you anything id omit those numbers only that they were EVEN is what you'd take away.
-
nissanfreak12
- Posts: 1709
- Joined: Sun Jan 23, 2011 4:07 pm
- Car: 92 300zx 2+2 TT
- Location: Denver, CO
Re: piston rings shot?????
PCV needs to be checked. If you are pushing out the dipstick that often or much, the pressure from the crankcase has to escape somewhere. This is a classic sign.
Now, the blue smoke could also be the PCV as well. Start with the simple stuff.
Now, the blue smoke could also be the PCV as well. Start with the simple stuff.
Re: piston rings shot?????
what oil are you using and how old is it?
yup blown piston seals. not necessarily the rings. it could be warped bores, piston damage, a failed head gasket/ cracked cylinder rings leaking between cylinders such that on the compression stroke it leaks into the next cylinder on an intake stroke, forcing exhaust back out into the intake, rod bearings or anything that affects the gas tight seal between the combustion chamber and crank case. excessive crank pressure is caused by the combustion chambers farting out combustion gas and the rings wont coat the cylinder walls with the correct amount of oil, leaving too much which gets burnt. blue smoke is burning oil. at boost the oil gets hotter and hence flows more easily into the combustion chamber where its dragged into.
cars can run perfectly fine with a melted piston top and small holes in the piston with negligible performance drops. my daily driver runs fine, passes emissions and has a fair amount of grunt for an old nubira even though one of the cylinders is melted and doesnt sit right in the bore. it does try to push out every seal in the engine though.
you can inspect the bores with a cheap inspection camera. about 20 bux on ebay for one that will connect to your phone. stick it down the spark plug holes and crank the engine around to the bottom of the stroke on each piston. look for any lack of uniformity and up at the valves and post back picture results. you could also find a good mechanic to work with you. find an owner operator basic shed type mechanic or engine specialist that tends to work on older cars like hot rods because crims tend to launder their money into the hundreds of thousands of dollars they pour into flashy cars, hold cash in your hand and ask if you can borrow his inspection camera for a short time just to look down your spark plug holes in the car park or if he will come look at them once you've taken the plugs out for him. they're usually willing in my experience to make some quick cash off the books especially if you dont act like a retard. also dont mention things like reciepts or doing it off the book because that's the kind of thing a narc would do.
yup blown piston seals. not necessarily the rings. it could be warped bores, piston damage, a failed head gasket/ cracked cylinder rings leaking between cylinders such that on the compression stroke it leaks into the next cylinder on an intake stroke, forcing exhaust back out into the intake, rod bearings or anything that affects the gas tight seal between the combustion chamber and crank case. excessive crank pressure is caused by the combustion chambers farting out combustion gas and the rings wont coat the cylinder walls with the correct amount of oil, leaving too much which gets burnt. blue smoke is burning oil. at boost the oil gets hotter and hence flows more easily into the combustion chamber where its dragged into.
cars can run perfectly fine with a melted piston top and small holes in the piston with negligible performance drops. my daily driver runs fine, passes emissions and has a fair amount of grunt for an old nubira even though one of the cylinders is melted and doesnt sit right in the bore. it does try to push out every seal in the engine though.
you can inspect the bores with a cheap inspection camera. about 20 bux on ebay for one that will connect to your phone. stick it down the spark plug holes and crank the engine around to the bottom of the stroke on each piston. look for any lack of uniformity and up at the valves and post back picture results. you could also find a good mechanic to work with you. find an owner operator basic shed type mechanic or engine specialist that tends to work on older cars like hot rods because crims tend to launder their money into the hundreds of thousands of dollars they pour into flashy cars, hold cash in your hand and ask if you can borrow his inspection camera for a short time just to look down your spark plug holes in the car park or if he will come look at them once you've taken the plugs out for him. they're usually willing in my experience to make some quick cash off the books especially if you dont act like a retard. also dont mention things like reciepts or doing it off the book because that's the kind of thing a narc would do.
this is a bad idea long term because it will interfere with MAF readings and the vacuum system the turbo, AIV, EGR and other systems are actuated by. it already does this when it pops the dipstick out and sprays the engine bay with oil. venting the crank case will solve the oil spray only and cause a host of other problems.lexcrob wrote: Try venting your crankcase breather hoses to atmosphere.
Re: piston rings shot?????
I should also add that the wrong oil or too much oil can also cause excessive crank case pressure but I assume that you have checked this. for the z32 I recommend changing the oil as soon as the oil pressure gauge starts to rise higher than it does on fresh oil which should be nothing at idle and barely anything up to 7psi of boost.