I've got an 02 Cav w/ a 2.2L that has been running rough. Scan test shows a Cyl 3 Misfire. I checked spark and fuel injection and they're fine. The compression on cyl 3 is about 40 psi, while the other 3 cylinders are around 150 psi.

Does anyone know a common cause for the low compression on this particular engine?

 

Either a leaky/sticky valve or bad rings would be my assumption. I guess it could be a head gasket too.

 

Thanks for the quick reply.

Any idea what tests can I do to see which is the cause?

 

I dont want to tell you to tear your engine apart and find out that isnt the problem, hopefully someone else can chime in and give some advice. I just dont know your engine specifically.

Some things to check:

1 Is there coolant in your oil?
2 Is there oil in your coolant?
3 Can you feel air with your hand by the bad Cylnder if somone else cranks it?
4 Pull the valve cover and turn the engine with a torque wrench or breaker bar and watch all the valves , look for one sticking. Could be a damaged valve too that you wont see until its apart.
5 If its the rings, you need to basically rebuild the motor.

 

Mike is right do those test and report back to us. At this point you would be lucky if your headgasket is blown! The reason I say this is a headgasket is cheaper then getting you engine rebuilt. It could be that The headgasket is cracked by your weak cylinder. I had the same problem on a jeep I owned there was no Antifeeze in my oil but my head gasket was cracked. When and if you take your head off be sure to take it to a machine shop and have it resurfaced and also perform a valve grind and replace valve guides if needed. Hopefully your head is not cracked. The machine shop will magnaflux it and tell you if it is cracked or not. Good luck and let us know if you have any more questions!

 

With the engine running I felt around the head gasket with my hand and listened with a stethescope, but no sign of a leak around that cylinder. I took off the valve cover and watched the valves close properly as the engine was cranked over.

There is no sign of antifreeze in the oil or vise versa, but I do smell a hint of gas in the oil.

 

Rings! Thats how gas gets in there. I am sorry you have to go thu this if you have a bad set of rings. I guess your next step would be to verify this with a shop and get it rebuilt, are you going to do the work yourself? If you have never done it , I would suggest a shop do it with a warranty.

 

Ok thanks, that's kinda what I thought you'd say. I'm considering doing it myself, but it's the wifey's car and she may not let me!

 

Is it a possibility that there is crack in the head gasket allowing a leak into the crankcase and not to the outside of the engine?

 

I guess anything is possible, you have to remove the head anyway, once its off then the investigation begins when you can see the top of the lower end and the cyl walls.