gnosis

I'm experiencing pinging, but only under very light throttle at between 2000 and 2500 rpm. The throttle that causes this is cruising throttle, with very light load on the engine. Any more or less throttle/load stops the pinging instantly. It gets worse as my oil temps move above 80 deg C, but the rev range and throttle position remain constant.

Any ideas what might be causing this? I can't figure out what it might be since the only pinging I've experienced gets worse with increasing engine load, but that isn't the case in this situation.

PorscheDude1

Try cleaning the MAF sensor.
Check the air filter.

RajDatta

You could have severe carbon deposits in your combustion chamber. What kind of gas are you using?
These engines gunk up around the intake ports and this could possibly be happening in your combustion chamber.
I would start by running premium gas and running an injector cleaner. A compression check would also help to determine if you ahve too much carbon deposits.
Raj

rdhayward

I'd follow Raj's advice, naturally, and search for causes of a lean-running condition. Inadequate fuel pressure or supply can come from a variety of sources.

With old carbureted engines, a part-throttle pinging condition would lead me to suspect a vacuum leak somewhere. And since this is an inexpensive thing to check (without a vacuum guage): idle the engine and spray some starting fluid around the intake ports. If the enginer revs up, that means the starting fluid (ether) is getting sucked in and burning. On the 968 engine, the intake manifold gasket itself is probably the only thing I'd be concerned about over time.

968workaholic

Seafoam or RunRite make an intake and fuel system cleaner that works pretty well. It removes most of the gunk that builds up on the back of the intake valves as well as in the intake itself. Short of taking the head off and manually cleaning the top of the pistons and the intake runners those are your two best options, aside of running a high grade gas.

RajDatta

Max, just curious, why would you consider carbon buildup on back of intake valves as a possible culprit? If anything, I would expect that to lower your compression from lack of a complete seal. This would have the opposite effect of pinging, correct?

Raj

gnosis

Thanks for the replies and suggestions. No solution yet, despite checking the things mentioned in this thread. I'll repost once I cure it.

968workaholic

Not the sealing of the valve but on the back of the valve face, around the stem. The carbon soaks up fuel, causing a leaner mixture. Meaning higher temps and a higher chance for the motor to ping.

RajDatta

I have never ever heard of this soaking enough gas to cause a lean mixture. I guess we can agree to disagree on this one.
Raj

968turbos2

Try looking for a vacumn leak specifically in any of the EGR system hoses.

Todd951968

Are you running a stock chip? I had a very similar problem, only it happened at 2500-2800 rpm. with light throttle but more load...like going up an upgrade at very light throttle , trying to maintain speed.

I tried changing the fuel filter, switching gas, ran premium as always, spark plugs, compression check, fuel system flush, took it to a dealer, etc.

What fixed it was swapping back the stock chip. I think that these performance chip manufacturers are pushing the limits on the ignition timing on the cars to get the most horsepower possible. Most cars are fine with the chips but every once in a while one can't handle the aggressive mapping for whatever reasons. Maybe the tolerances are so close?