96 Lumina sucking air through oil fill

stepjam · #1 05-08-2005, 10:28 PM

I'm stumped. I was doing a routine oil check on my 96 3.1 Lumina with 113K. I had the engine running, and as I removed the oil filler cap, she stalled hard. She wouldn't restart until I replaced the cap. That's when I noticed that the engine is sucking air through the filler, big time. It's also sucking air down the dipstick shaft. The PCV valve is buzzing like crazy, because it's fighting suction in both directions. When everyhting is buttoned up, the engine starts and runs fine, no hesitation or misfire.
She doesn't use any oil, coolant level is fine. Any suggestions???

tblake · #2 05-08-2005, 10:47 PM

sucking air through the dipstick, and oil filler? Is it on time? Sounds very strange

jeffcoslacker · #3 05-09-2005, 05:58 AM

Sounds like the breather side of the PCV system is blocked.

stepjam · #4 05-09-2005, 10:50 AM

Would a faulty EGR valve cause this?

jeffcoslacker · #5 05-09-2005, 11:06 AM

Quote:

Originally Posted by stepjam

Would a faulty EGR valve cause this?

No. The PCV system is not a dead-end system. there is suction at one side, where the PCV valve is, and a vent on the other side, to allow air in. Otherwise, it would create a vacuum in the crankcase like you are seeing. The idea is to create an air flow through the crankcase, and pull vapors out to be recycled through the intake.

Need to find the vent, an unblock it. I believe it comes into the duct between the MAF and the throttle plate..

I'll go look at mine.

jeffcoslacker · #6 05-09-2005, 11:08 AM

Just went out and looked. On my '97 it is the black plastic line with the elbow going into the top of the duct, just ahead of where it clamps on the throttle plate. The other end goes back to the rear valve cover, I presume, I didn't look that hard.

jeffcoslacker · #7 05-09-2005, 11:13 AM

One piece of bad (possibly) news, the only time I've ever seen the vent side get blocked was on engines with intake gasket or head coolant leaks, the resulting oil/coolant sludge is stout enough to build up and plug the line. Hopefully that's not the case here.

you haven't noticed that on the stick or the cap, right?

stepjam · #8 05-09-2005, 12:11 PM

No, the oil is clean, and there aren't any deposits on either the filler cap or the dipstick. I just started the car, she kicked right over but there is the beginning of a hesitation just as the engine fires.

jeffcoslacker · #9 05-09-2005, 02:02 PM

I was assuming that you've checked the pcv for proper operation, but maybe we better go back to it. It should have a heavy rattle to it when you shake it, the check ball should be moving around very freely. Try spraying some carb cleaner or WD-40 through it and see what happens. A pcv stuck open can cause this too.

stepjam · #10 05-09-2005, 02:50 PM

Nope. I tried that already, by removing the PCV valve, cleaning it, then starting the car without it (I left its insertion hole open), and the car just barely started. very rough idle, and sucking like mad through the PCV port.

jeffcoslacker · #11 05-09-2005, 04:21 PM

OK, then try removing the breather tube, and see if it's blocked. You could just pull it off the intake duct end and see if you can blow through it. If not, you've found the problem. If not, I don't understand what's happening.

It won't want to run with the vacuum line off the pcv. That's a huge vacuum leak. But if you plug the line, it should run fine. Then you could see if that relieves the suction in the crankcase when it's running. (it should)

jeffcoslacker · #12 05-09-2005, 04:28 PM

See, the pcv works kinda in a see-saw fashion. The pcv valve is piped to intake manifold vacuum. The vent side is piped to ported (before the throttle plate) vacuum.

When idling, intake vacuum is high, and the pcv check valve moves one way, and allows flow in one direction. When you step on the throttle, manifold vacuum drops, and ported vacuum rises. There is almost no suction at the valve at this point, so the flow goes toward the vent side. As RPM's build, manifold vacuum comes back, and stabilizes. The pcv is there to prevent hard vacuum being built in the crankcase, like you have, and to ensure a cross-flow through the crankcase at a variety of different load conditions.

radioman2002 · #13 05-17-2005, 07:33 AM

Sounds possibly like a bad intake, or gasket. If it's sucking air into the PVC hole, then it's pulling air where it shouldn't. PVC pulls air from the valve cover hole not into it. Same with the oil filler, sounds like air is being pulled into one of the cylinders through the valve cover, I would go with a bad intake gasket, weird, but thats my best guess.

richtazz · #14 05-21-2005, 11:15 AM

I agree with Radio. its either an intake leak or a head gasket/cracked head causing compression gasses to leak into the crankcase

stepjam · #15 06-05-2005, 01:32 PM

Okay, I've narrowed it down to the PCV line. When I remove the line and PCV valve from the valve cover, the "suction" at the oil filler and PCV port disappears. Obviously (duh) all of the suction is through the PCV line. So, what would cause such abnormally high suction through it?

I should add, the car has been sitting for two weeks. She started right up and is running like a champ.

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