What does a bad pcv valve cause?

dschrier · Sep 11th, 2002, 06:06 PM

What problems would a clogged pcv valve cause? I tried changing mine cause it's caused with gunk along with the hose but I can't get the thing off myself so I need to go get it done at a garage. Would a clogged valve cause pinging possibly? I seem to ping even on hot days with 93 octane fuel. I have an all stock 90 b12 with 148,000 miles.

Sep 12th, 2002, 09:35 AM

I'm no expert, but I found this web site recently: http://autorepair.about.com/library/ts/bl303a.htm. It describes common engine performance symptoms and their causes. The problem you're describing sounds like:

Quote:

There is a rattling noise from the engine when you accelerate:
Your car runs well all the time. But when you press on the gas pedal to accelerate or to go up a
hill, the engine rattles like the cylinders are full of marbles.

Possible causes:
1.The ignition timing may be set wrong: Adjust ignition timing.

2.The engine may be running too hot: Check and repair cooling system.

3.There may be a vacuum leak: Check and replace vacuum lines as required.

4.Incorrect grade of fuel: Fill with the correct, or higher, octane fuel.

5.There is an excessive amount of carbon built up in your engine: Clean carbon from
valves and combustion chamber. (Not a DIY job)

6.There may be a fault in the computerized engine control system: Check engine control
systems with a scan tool. Test circuits and repair or replace components as required.
(Generally not a DIY job)

This site explains some possible symptoms of PCV valve failure as:

* Engine uses more oil than normal, and there is (or is not) some smoke from the exhaust. <OR>
* Engine is using more oil than normal. Oil puddles under the car when parked:

It didn't give any other symptoms related to PCV valve failure. I'm sure there are some though.

Anyone else, feel free to dispute or confim this.

Jon

bahearn · Sep 12th, 2002, 11:55 AM

The PCV valve is a simple ball check valve. It is oriented so that vapor flows from the cam/valve cover to the vacuum source, usually the intake manifold or tract. It has two failure modes:

Stuck open
Stuck closed

Stuck open would allow normal flow of crankcase oil vapor to the vacuum source, but would allow intake pressure pulses to flow back into the cam/valve cover. This could allow gasoline into the engine cases. Gasoline has almost no lubricating properties for high-pressure applications such as crank bearings and cam followers.

Stuck closed causes a slight power loss. The PCV valve has one major function and one minor side-benefit: it allows crankcase oil vapor to be burned instead of venting to atmosphere and the vacuum applied to the crankcase reduces crankcase pressure slightly. Pistons moving up-and-down pump crankcase air as wells as intake air, using horsepower to do so. Reducing the crankcase pressure reduces pumping losses.

Your pinging has nothing to due with the PCV; if it's gunked up and not rattling, that's an indication of badly worn rings and valve guides.