It only takes a valve to be stuck open a very small amount to cause this,the way you would check is to check each valve at its tdc,it might be a little looser than the others,because it did not retract back all the way. If you want to find a bad valve you should do a compression check,if one is stuck you will not have compression on that cylinder. Do you know how to do a compression check?

 

Not really, I know it involves a pressure gauge that attaches to spark plug hole. I would assume I would get the gauge, plug it in, remove the spark to the engine and turn it over a couple of time. I just don't know how to interpret the results.

Am I just looking for one cylinder with a much lower pressure reading?

 

you can do that with your finger too, eheh not kidding...

 

if you want to do a compression check just get yourself a compression tester at the local auto parts,remove all your plugs,and coil wire,check each cylinder and see where they are at,you want between 120-150lbs,or do like fantic238 said and and hold your thumb against the spark plug hole,if it does not have compression,you will know,it will not tell you what the pressure is,but it will tell you if there is compression

 

If your cat conv has or is failing it will prevent you from starting the engine and will cause exhaust to come out of the intake! Unbolt it if rust will let you- if it starts it may still run rough because the computer wont be able to see any change at the downstream o2 sensor , but at least you will know if the cat is causing your problem

 

good point.

 

Ok, so I went to the local auto parts store and rented a compression gauge. Long story short, I don't know if it was operator error or if I rented a broken gauge, but I couldn't get any one cylinder to blow the same reading twice. We are not talking about the difference between 140 and 160, I'm talking about from 60 to 160.

While I had my girlfriend over helping, I went ahead and pulled the valve cover off and watched the rocker-arms as it turned over. I don't know what I was expecting to see (maybe flashing lights or a small "out of order" sign on my #2 intake valve) but I didn't see anything out of the ordinary.

I'll have to go out and grab a different compression gauge tomorrow and see if it's me or the gauge (hoping it was the gauge, don't know how I could screw up something so simple...). I'll have to try the cat. Converter as well.

I'd like to say now, in case I forget down the line. Thanks for all the help guys. This all would have been much more painful if not for your help.


EDIT: Also, I couldn't get my thumb over the spark plug holes, but I could jam my finger in there. Couldn't tell a difference in one cylinder from the next, but that might just be me not knowing what to look for.

 

if you had the guage in the spark plug hole and it was tight on every cylinder checked,your readings are correct,you are suppose to turn the engine over 6 times. Did you write the readings down?#1 being the front, If they turn out to be what you just said,it is a serious problem

 

Uh-oh... Hoping for bad gauge, but here are my tests:

Series #1:
Pistons going from front to back
P1: 100
P2: 100
P3: 60
P4: 150

Series 2
Pistons from front to back
P1: 90
P2: 130
P3: 145
P4: 140


I checked them from back to front, actually (because that front cylinder is such a pain to get to the spark plug hole) and when I was done with the second series I went back to P4 and got 90...

If those records are accurate, what on earth does that mean is going on in there?

Oh, and just to clarify, if I left the gauge in the plug, reset, and test again it gave the same result. It was only when I came back later that it reported different.

 

If those are the correct readings,it could be valves,or head gasket. It is hard to tell. The guage you have is new correct?if it is you just need to do them all again,a couple of times,there is nothing consistent there that points to anything honestly.
Make sure the guage is screwed in all the way and tight.

 

The gauge is used. I got it from o'rielley loan a tool thing.

I'll get another set of readings tomorrow, followed by a fesh gauge with 2 sets of reading. That and remove the cat. converter, and see if that does anything.

 

dont think so??

 

Failing cat that is not completely plugged could cause inconsistent readings. When the honey comb structure falls apart it can move around with the exhaust that is trying to get past, thereby potently causing erratic and inconsistent readings.hope you locate your gremlin soon! Barring a failure of your cat, you might want to check any and all wiring that is near to the exhaust.

 

Wait, how likely is it that something in the exhaust could cause my problems?

I just remembered while I was hanging the tank back in there, I noticed that at some point after I replaced the clutch (couple of weeks before this problem began) the exhaust came off its hangers and has been kind of dangling.

If the exhaust could cause this, what (aside from the catalytic convertor) could cause this?

 

What happens with cats is they can become plugged overtime and restrict flow,then engine does not breath well and can cause your problem,the other thing is the cat can come apart and end up in your muffler resulting in the same problem. But when you do a compression check today just make sure your plugs are all removed,it will have good results.
And engine is nothing more than an air pump,if it cannot get air or get rid of it,it is like have a breathing problem or your nose is clogged,you do not do well,either will your engine.
I had the cat on a 89 grand am plug and blow the head gasket.
I think once you do a compression check and check cat if you can get it off to look at it,if nothing is clearly wrong,I would suggest again to have a shop look at it.