Cylinder 3 Misfiring

[Gortonsbulldog]

I have a 96 Gs model that is stock and I am getting a P0303 misfire code. I have replaced fuel filter, spark plugs, iginition coil, and have performed a compression test with readings of 212-210-60-212. I also have checked timing and it seems to be off a tooth or 2 on the exhaust cam. Would this cause the low compression on cylinder 3. Did a wet test in cylinder 3 and compression on went up slightly to about 70 on cylinder 3. If it is a vavle issue is the car safe to drive until I can save up for a new, used or rebuilt engine.

 

[boost97gst]

I wouldnt drive it much. Alot of fuel is getting in without burning and washing down the walls causing oil contamination and other bad stuff with the bore, skirt, and rings. Leakdown test asap. Dont be shocked if its your rings. Just went through this myself and the wet test i did at first showed only a 10psi change. I ruled out the rings but after a leakdown it was confirmed, rings were bad in my #2 cylinder.
Doesnt necessarily have to smoke or anything, mine didnt/doesnt but the (guessing here) compression ring must be cracked.

On the other hand you may be out of time enough to have bent valves but it usually happens in more than one cylinder so you would see similar numbers on another cyl too.

 

[Rock2610d]

3 of those are really good for a NT motor. I think readings should be 170 to 225 psi. The 60 is really poor. Are you really sure of the 60 psi? Seems a little odd that a motor the has over 210 psi on 3 cylinders would get a bad valve....but it does happen.

I would not drive it like that. But if you have to I would pull injector wire so injector is not pushing fuel and pull the plug wire so it is not firing. It will be hard on the other rods, pistons, cylinders, and bearings. Not to mention the ECU will be completely confused. Air in will be hard for the ECU to pump enough fuel to to compensate.

In other words the ECU will see say 10 pounds of air. It will want to provide enough fuel for that air. It will not be able to and the other 3 cylinders will run VERY rich, which could make them go bad.

 

[boost97gst]

^^^ truth. Rock makes a great point. I forgot about that. When one cylinder effectively dies the ecu compensates by dumping way to much fuel to try to get to stoich. Washing down the walls on the other 3.

Leakdown time, like i said.

 

[Nick2g95]

I just experienced a similar problem myself. Definitely check everything before you assume the worst.
Check your cat and your O2 sensor. that did it for me