QuestionTed,
I have this persistent problem with my 1990 Toyota Pickup with a 22R motor. The truck has low miles for a 1990 model (about 103K) and is in great shape mechanically. Over the last few years, however, it pings moderately under load (accelerating, climbing inclines, etc.) when the engine is cold and warming up. Usually it stops once the engine reaches normal operating temperature, although sometimes it persists if I'm driving on the highway.
I can usually tell when the pinging will start to subside by watching the temperature gauge. It rises to the normal position (a little less than halfway), then backs down ever so slightly in normal driving once the thermostat opens (has the 195 degree thermostat I believe).
The kicker is that this only happens, when the ambient temperatures start to cool off. I live at an elevation of about 4,200 feet and lately the evenings have started to get more fall-like and cooler. Sure enough, like clockwork, the pinging is back. Interestingly, however, when the temperatures are very hot (summer) or very cold (winter) there is no perceptible pinging. Only when it is cool, which is usually between late August and early November here.
I've tried different grades of gasoline (currently running midgrade 88 octane) and the pinging is mitigated somewhat with 91 octane fuel, although some light pinging can still be heard occasionally. The truck is kept in tune regularly, but this doesn't seem to make a difference. I've read that pinging can be caused by a number of things, including a faulty egr system. Could there also be an issue with the vaccum advance diaphram on the distributor? Any other ideas about what I might look at?
By the way, the truck is not equipped with the Toyota High Altitude Compensation (HAC) kit, which the owners manual generally recommends for carbureated models running at this elevation. It was running fine for years without the HAC kit before this problem surfaced, however. Other things you might want to know and that may or may not be relevant is that the timing chain was replaced about 20K miles ago and the carb was rebuilt roughly three years ago at a local mechanic's recommendation (although I don't think it actually needed it).
Thanks in advance for any suggestions.
AnswerPinging can be caused by a few things like:
The timing is too far advanced
The compression is too high because of carbon builtup
The egr system is not functioning
The octane rating of the fuel is too low
The engine is running too hot(doesn't seem to be the case here)
The fuel/air mixture is too lean(possible carburetor problem) this may explain why the problem is more prevalent with a cold engine, when at this is the time it needs a richer fuel mixture.
The first thing I would check is the basic engine timing and make sure the advance is working correctly.
If the problem was not there before the timing chain replacement I would suspect that the cam timing may be off.
Then I would do a compression test to see what the readings are(about 170-190 psi is considered normal.)
You may also want to check for a possible blown headgasket, introducing coolant into one of the cylinders will cause pinging, especially when cold.
