Pinging--ARRGH!
 

Technical question(s):

Well, for the past year or so I always use premium (whatever the highest octane available is). Usually Chevron (with Techron(tm)). I go one further and dump in some octane enhancer to raise it a few points (maybe from 92 to 92.2 if I'm lucky).

My car was still pinging rather badly in 2nd and 3rd in the 4500 RPM range when under load. Of course, I always let off the gas as soon as it starts. And it only happened when the car was warm (but then, I don't exceed 3500 before it's warm).

A few months ago I had my SC in at my wrench's for de-carbonization. My wrench used "Dr. Bob's Magic Juice" or something to decarbonize the valves, etc. He removed the injectors, cleaned them, cleaned the plugs, you name it. He said that my timing was retarded as much as possible and that it wasn't pinging anymore.

He was right--for about 2 months. I drove the snot out of it, revving up to 5500 to 6000 regularly in 2nd and 3rd, disbelieving that my problem had been solved. Well now, the pinging is back. However we've also had 100+ degree heat regularly and my oil temp sometimes gets as high as the 9:00 position (right smack in the middle--this isn't unusual for summertime driving). We've also got that crap oxygenated gas out here in AZ.

My question: could this be a distributor advance issue? Is it possible that my distributor is over-advancing the timing in the higher rev ranges? Or can carbon deposits form within such a short time? It's also about time for a valve adjustment--could tight valves cause predetonation? I guess if a valve is tight and not seating completely when closed, it would heat up more and possibly ignite the mixture early. But then wouldn't I have a burned valve and my engine be running like scheisse? I can't hear ANYTHING tapping in the valvetrain so I'm thinking the clearances are pretty small, if they exist at all!

Any help greatly appreciated!


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blue
'81 SC Targa

What psi compression readings are you getting for each cylinder?

Question: What will a compression test tell? If it's to determine if there's a valve not seating properly, I guess a few leakdown tests would do the same, right?

My last compression test was on the PPI which was about 20 months ago. Can't remember exact numbers but I think they were all OK...

Thanks.

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blue
'81 SC Targa

[This message has been edited by BlueSkyJaunte (edited 07-05-2001).]

It will tell you if you are right on the edge of pre-detonation due to compression levels higher than expected. This might be due to carbon build up or piston/stroke setups higher than expected.

Run a bottle of Techron thru it. My 83 banged so bad when I first bought it, I thought I surely had a broken head stud. Ran a couple bottles of Techron through it and the knocking went away. I assumed it was just carbon buildup.

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Robert Stoll
83 SC
83 944

Don--

Thanks. I'll go get a compression test done.

Never thought I'd have to worry about it being too high! We're all usually afraid of it being to low (broken/pulled stud).



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blue
'81 SC Targa