blowby question

[95AWD6Bolt]

I have heard of people who think that they have blowby and it turns out to be a pcv valve or something. Could this pcv valve also cause low compression? If so i am going to be very happy.

 

[turbo98eclipse]

pretty sure that this is a no. compression is created/held by the piston rings. what seems to be your problem?

 

[dnhieu]

a bad pcv valve would not cause low compression. bad piston rings, or bad headgasket would be your best bet tho...

edit: but to answer your question a bad pcv valve will make you seem like you have bad blow by during a boost leak test.

 

[GST98BIG16G]

sorry to tell you , low compression (rings ) not PCV. DOes your car smoke?

 

[nube90]

Yep PCV helps ventilate the gases in the engine right? What where the test numbers?

 

[dnhieu]

you are right on man...

 

[turbo98eclipse]

you may want to pull your plugs to check for oil deposits...that's always a tell tale sign of leaky rings

 

[95AWD6Bolt]

Im not smoking or anything but we did a boost leak test yesterday and had air comming through the breather on the valve cover and when we opened the oil cap pressurized air was comming out. So when we got done with that we did a compression test and it averaged 70 across the board. However, right now it runs fine just has a high and moving idle. How am I getting air by without smoking?

 

[nube90]

70 across is your battery low? those numbers are horrible the service limit is 133psi.
Just because you have low compression dosent mean your car should be smoking oil rings control that, if your compression rings are bad that would cause low compresson without the smoke.

 

[95AWD6Bolt]

Would the battery cause it to be that low?

 

[turbo98eclipse]

there are three rings: two compression rings and an oil ring. you could have a bad compression ring and still have a good oil ring. you did a boost leak test and pressurized your system. your system was holding good which is why the pressure released when you opened the oil cap.

70 for compression?? I'd suggest you get new rings for all cylinders. but with numbers that low across the whole board, you may want to re-test with a new tester. yours may be faulty

 

[WeaselHack]

Were you testing on a cold engine? You should always do your compression tests when the engine is near operating temp. Also, before digging into your engine to replace rings, perform a leak down test, to determine in fact if its rings, or valve seals or head gasket. As others have stated make sure you have a fully charged batt too.

Take a look at this:
Leakdown: http://www.geocities.com/dsmgrrrl/FAQs/leakdown.htm
Compression: http://www.geocities.com/dsmgrrrl/FAQs/compression.htm

EDIT: Since it sounds like you have access to an air compressor when you did you boost leak test, you may be able to perform a ghetto style leak down test by using the screw in fitting on the compression tester and an air tool quick disconnect to pressurize the cylinder and listening for leaks at the tailpipe, oil cap, etc. The only downside is without the leak down tool, you won't be able to determine the percentage of loss on each cyl but will give you a good starting point.

 

[95AWD6Bolt]

Yea i would say that it was at least thirty minutes after the car was shut off that we did the test.

 

[95AWD6Bolt]

Would a cold engine affect the compression that much? I have Ross pistons on the stock bore, or at least thats what I was told when i bought the car, i still have the receipt that the kid gave me for the engine. Im going to try and check the compression again with a warm engine. If it comes up low again i am probably just going to have to buy a stock shortblock and rering the pistons in my spare time.

 

[turbo98eclipse]

dont forget what i said about the tester itself... try testing another car which you KNOW has good compression if possible