Ok, interesting problem but not to complicated to determine root cause. HOWEVER, it could be one of several things that are more than likely going to require the engine to be pulled down. The whole time I was reading that posting I was thinking "Where is the compression test, where is it?" LOL. Then I got to the end and saw you'd done it!!! (190 is fine)
With oil fouling the plug in that cylinder, this slants the problem to me to be that the compression could be lost due to cylinder wall damage or compression/oil ring ring being blown perhaps or a leaking valve guide seal OR blocked up oil return holes in the head. BUT, you've GOT compression and you also say the engine is smooth on all four cylinders yet gets rough when the wire is removed from number 4(the one in question). hmmmmm....Here is my potential list of what could be the problem. More time with the car would be needed.
A) Cylinder number 4 has a worn out valve guide seal on either the intake or exhaust valve and is leaking oil. This seal was weakened and woren out POSSIBLY because of excessive backlash of the valve in the metal casting guide in the head. Hence the noise when FIRING, since you say if it is not FIRING, just spining over on the other 3 cylinders, there is no noise. Keep in mind when that cylinder is firing, things are stressing in that cylinder.
B) Possible piston wrist pin failure/damage or connecting rod bearing failure for that cylinder.
C) Possible worn rings in that cylinder. Does not sound likely in this case other than the presence of oil on the plug which I assume is wet motor oil and not "fouled or burnt", right?
D) Possible rocker arm backlash/failure for one or both valves in the head. (unlikely due to no different dynamics here if it is running or not and your noise is variable based on if the engine is running or not.)
E) Some type of valve train failure in the head that is becoming stressed when that cylinder is firing.
**Let me think on this, I have to go to dinner now and am out of time.
I will see what else I can think of, but you have some type of engine hardware failure either in the crankcase area, or the head and I am more than sure it will have to be torn down to determine it. Let me know what else you have done/tested....
Originally Posted by MrDee
Hello. I've exhausted my resources at hand with my car. ('gear head' relatives and friends).
My tracker is making a fairly loud and high pitched 'pinging' sound. It's a distinctive metal on metal sound that is in time to what seems to be one cylinder.
BTW.. It's a SOHC 16valve.
It is also blowing large amounts of white exhaust. The exhaust seems to smell a bit of fuel (i'm not certain of this though.. not good with exhaust smells...it all smells like exhaust to me).
The spark plug in the 4th cylinder was fouled and seemed to have motor oil on the electrode. All the plugs were replaced. I removed the valve cover and all valves seem to be opening and closing properly. I borrowed a compression guage and all 4 cylinders are holding at about 190psi after 3 cranks (father inlaw told me that's fine).
Thanks in advance!