AutoAudioGuru

Wouldn't a dropped valve seat cause compression to be poor? The backfire/ping is not on every revolution, which I would also expect to occur if it was something as traumatic as a lost valve seat. Hopefully we won't need to pull the head to see, but it is looking that way.

My mechanic will do this test tomorrow and I'll report back. I would not, however, expect that a blown head gasket would cause the mechanical "ping" sound that immediately preceeds the internal backfire.

I hope someone will be able to help my mechanic diagnose a problem. We recently purchased an '87 GL-10 Turbo Wagon with about 86k miles. I'm not terribly familiar with these vehicles, so forgive my limited description of the circumstances. After coming to a stop at an intersection, the engine died. At that point my son noticed that the temperature was at full hot. Initially the engine would not turn over, but within a few minutes it did start, but ran poorly. After filling the radiator with water and coolant with the engine running, the temperature remained normal but the engine continues to miss with the sound of a backfire and almost, possibly, but not sure, the sound of a mechanical ping at the same time. There is no water in the oil. We took the car to our trusty mechanic who verified that the compression is good in all four cylinders, however the driver’s side cylinder nearest the back of the engine is not firing. Removing the spark plug wire makes no difference in the engine’s ability to run. A check of the connected spark plug shows that spark at the plug is fine. The injectors seem to be firing in fuel. Using a mechanic’s stethoscope, it appears that the backfire and sorta-ping noise is most severe just under the turbo air intake manifold at the center of the engine. Prior to the overheating incident, which appears to be caused by a leaky radiator, the upper cam shaft seals had been leaking oil. We were planning to have the timing belts, water pump, and cam seals replaced anyway. There is no record that the timing belts had been replaced. Our mechanic is stumped. Short of a tear down, he really does not know what is causing the problem. Any ideas?