Annoying Pinging Problem...Any Ideas?

[cwinters01]

Hello All:

My 83sc (117K Miles) in general runs excellent at high rpm...but for at least 5 summers now I have found that when the weather gets hot the car will start to ping at rpms greater than ~ 4K. The interesting part is that it doesn't do it all of the time. It seems like it likes to ping mostly after I have initially driven the car, turned it off, then drive it again within a few hours...(it might also do it on initial startup too, i just might not have noticed it if it has).

It doesn't matter what brand/octane of gas I use, I've bounced around between grades of chevron to see if that made a difference-nope.
Someone told me to try the fuel accumulator, so I replaced that (and the fuel filter) last summer, but that didn't fix the problem.

It almost seems like the timing is changing for some reason? One other thing: it seems like when I am getting the pinging, the car also does a little idle searching, between 950 and 1250 or so...it doesn't generally do this, or at least not to this degree.

Again, this is only in the hot summer months-when the weather gets cooler, my problem goes away.

Anyone out there experience this problem too, or would you hopefully know what I might do to fix it?

Thanks ahead of time,

Christian

[kang]

Have you tried fuel system cleaners, like Techron?

[cwinters01]

Thanks Kang, I do run Techron thru it every few months...

[911pcars]

Have you checked the ignition timing? Too much advance with too much load (e.g. low revs plus large throttle opening) and it'll ping.

Increased ambient and engine temperature also predisposes the engine to detonation. What are your oil temps while pinging?

Excessive carbon buildup in the combustion chambers is also a possibility, thus the Techron suggestion. Careful using this stuff. It's a great solvent, but too many applications can decrease the protective oil film (valve guides and cylinders).

If you suspect excessive carbon (e.g. higher compression test readings), check the archives on using a water spray to blow out the carbon.

Sherwood

[RoninLB]

Originally posted by 911pcars

Have you checked the ignition timing?

ditto for sure.

check the whole curve. If ok I'd retard it a couple of deg and see what happens.

[cwinters01]

Thanks Sherwood:
Have you checked the ignition timing? Too much advance with too much load (e.g. low revs plus large throttle opening) and it'll ping.
Since it doesn't have the problem all the time, just during the hotter months of the summer, and even then only when I drive the car, turn it off, and then start it back up within a few hours, wouldn't this be ruled out?
Also, my oil temps are definitely staying in the normal range, never getting to the upper bars...I haven't been driving it long enough at any one time for them to get there (generally the most driving I do is 1/2 hour at a time).

[Superman]

As the constable says toward the end of Casablanca, "Round up the usual suspects." Not just ignition timing but mixture also. Our cars are spec'd to run darned lean. On the edge, frankly. Ignition timing is fairly conservative. Mine is seven degrees advanced from stock spec and it does not ping. My mixture is perfect. Not lean, that is. And then there is the carbon buildup possibility. If you use Chevron gas, then you've done everything short of the water spray tactic. Water will remove carbon.

[cwinters01]

Thanks Superman, and all that replied. I guess looking into timing and fuel mixture is the consensus, so that'll be the next step.

Thanks again for the quick responses.

Regards,

Christian