I use Shell Premium excusively for my 911S and I do get occasional, momentary pinging when cruising at about 2500 rpm and moderately increase the throttle opening.

 

I just went through the same issue on my POS Saab 9-5. Running a tank of Shell Premium and a bottle of Chevron Techron fuel system cleaner straightened out everything. I agree that you likely have carbon buildup on the valves which will glow red hot under load. If hot enough the heat from the glowing carbon will ignite the fuel prematurely and cause spark knock.

I recommend running the fuel system cleaner right away. I pur some in and let my car idle in the driveway for a half hour-it cured the spark knock issue.

 

Don't rely too much on the Top Tier rating, at least from the standpoint of assuming that if a gas is not on the Top Tier list it is crap. For an oil company's gas to appear on the list, all three grades of gas must meet the Top Tier standards. Most brands of major suppliers' premium fuels meet Top Tier standards, but may not appear on the list because the regular and mid grade don't meet the standards. I have seen Hess stations and have used it a few times, but don't know enough about it to comment on quality.

Many people claim to use only Top Tier gas because they say they don't want to run gas containing ethanol, but if you go to the Top Tier website and read the formulation, you will see that the Top Tier formulation specifies 10% ethanol, unless the formulation has been changed in past couple weeks.

1.3.1.2 Base Fuel. The base fuel shall conform to ASTM D 4814 and shall contain commercial fuel grade ethanol conforming to ASTM D 4806. All gasoline blend stocks used to formulate the base fuel shall be representative of normal U.S. refinery operations and shall be derived from conversion units downstream of distillation. Butanes and pentanes are allowed for vapor pressure adjustment. The use of chemical streams is prohibited. The base fuel shall have the following specific properties after the addition of ethanol:

1. Contain enough denatured ethanol such that the actual ethanol content is no less than 8.0 and no more than 10.0 volume percent.
2. Contain no less than 8 volume percent olefins. At least 75% of the olefins shall be derived from FCC gasoline as defined by CARB (advisory letter, April 19, 2001).
3. Contain no less than 28 volume percent aromatics as measured by ASTM D 1319 or D 5580.
4. Contain no less than 24 mg/kg sulfur as measured by ASTM D 2622 or D 5453. At least 60% of the sulfur shall be derived from FCC blend stock.
5. Produce a 90% evaporation distillation temperature no less than 290F. as measured by ASTM D 86.
6. Produce IVD no less than 500 mg averaged over all intake valves.

 

Thanks for the word, Mac. FWIW, here's the 997.1 manual. I dunno what the numbers mean exactly but seems I've been mislead. I was told we could burn the gas found in Nowhereland _low-octane_ wise.

BTW, You have a good point: why anybody would choose to use cheap gas can't be explained in a happy way.

 

Tanked up with Chevron today. Will run the tank and then go through a bottle of Techron using Shell 93. I've always used Hess...may be time to change. Theres a dealer in town selling unknown brand ethanol free premium, but I'm not too trusting.

 

I'm very surprised that you can detect pinging or engine knock at all since you engine is equipped with an "electronic knock sensor" which retards the engine's timing when the device detects engine knock.

Maybe you do have a warranty/dealer issue.