My normally aspirated 850 is developing progressively worsening pinging. in a narrow rpm band around 1800. This is barely present, if at all, on 93 octane fuel, but gets much worse as the octane declines. No "check engine" light; no codes. Runs as smoothly as ever.

Any suggestions as to what to fix?

Hello there, Let me give you some food for thought.

Have you ever heard of Amsoil before? If you have not you should look into it. I have a 1995 Volvo 850 GLT Sedan and have been using the Amsoil Product throughout the entire vehicle. I originally started using the product about 2 years ago in my 4 WD vehicle and was impressed with the results. Now I even sell the Amsoil Products.

The Amsoil Synthetic products out perform all synthetics, sythetic blends and regular base motor oils that are currently on the market.

What your looking for will not require you to tear the motor apart. All you need to do is get what is called P.I. Performance Improver. A 6-oz bottle treats 10 to 15 gallons of gasoline and cost about $4.50 a bottle. It will dissolve and remove fuel system deposits along with other contaminants for improved power and overall performance in gasoline engines. It will even reduce PVC & EGR system deposits. It reduces exhaust emissions, improves engine idle, repsonse and starting. Works in both fuel injected and carbureted systems.

It's worth the look and the Money.

Also consider using a heavier motor oil, like 10w-30, 10w-40, or even 15w-40. And you can use the regular 87 octane gasoline as well.

If your interested in learning more I'll be glad to help you out and that goes for anyone even slightly interested. Give me an email at rpiescik@attbi.com.

Talk to you soon.

Just to change the variables...have you tried running a different brand? It can make a difference, as particular formulations can differ.

These electronically-controlled engines are self-tuning, and pinging is typically a timing issue. It's possible your ECU is getting bad data somewhere. Look for loose or worn hoses, etc.
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(98 S70 T5SE misc mods, mostly lighting) (92 940GLE)

Did your pinging start at the begining of the summer. In California, gas companies sometimes change their formulations with the seasons. I remember they did were required to do something with an oxygenating additive during certain months. I have no idea if that is still required.

Eric

And.. Run a can of BG44K through the gas on the next fillup. It's about $17, and so well worth it. I do it twice a year. Makes life really simple.. You'll notice the difference in 250 mile, and it gets better from there.

where do you get it?

Looks like you've done the test yourself already. Stick with high octane fuel--I use 91 Chevron on mine--instead of the minimum required per your manual.