1996, 850.

[david john]

Using unleaded 98 here in Australia and during the warmer weather do get some pinging noise when accelerating, fuel tank is about 1/8 full so will put some more fuel in it, I thought the 98 fuel would be better for the car,maybe I should go to the 93 or the green coloured 91 the fuel cap suggested, I have heard too that it might be an idea to change the spark plugs after a year or use so will do that, there are no vacuum leaks, may spray the mass air flow sensor as well, hope all is well cheers.

[scot850]

I would run the car on what is in your handbook or on the car sticker. What is your 850, turbo or NA?

Your fuel rating is different to North America, sounds more like the UK rating system. In Canada we have Regular, Mid-grade and Premium although some now have a 'super' premium. I would never run a turbo Volvo of this era on anything less than Premium as it is likely to cause a valve to burn. AI used to run the 93 850 GLT (NA) on regular around town, but for highway runs I used premium.

Spark plugs, cap and rotor are around 20,000 miles. On a turbo the gap is very important so check that,

I don't advise running the tank below 1/4 full on a regular basis. The pump uses the fuel to help cool it. Below 1/4 tank it starts to get exposed in the tank and run hot.

Pinging noise is normally associated with timing being off or engine running lean. Check your fuel pressure at the injector rail, for your car that should be around 42 psi.

Vacuum leaks can also cause issues as you mention.

Neil.