I notice on occasion that when I accelerate from a dead stop I get a knock out of the engine. Sounds like a spark knock. It only does it on the initial launch and then is fine. I have been running regular gas in the car - in the summer I will mix premium as I tow a boat. Any ideas if this is just normal operation ?

Thanks

Derek A.
87 245

Has it been knocking all the time or did it start this winter? Reason being, in some parts of the country gas is reformulated during the winter due to air pollution and I noticed on another one of my vehicles that I had to move to mid-grade during the winter due to a slight knock under load. Also, as an engine ages and builds up deposits in the combustion chamber the compression increases slightly which could affect the fuel requirement. I alternate adding mid and premium in my 1988 245A because I can tell the difference in power and it needs all the help it can get. Don't think it gets better mileage, but definitely has more spunk when accelerating onto the freeway. I use Chevron with Tectron and have always passed California's strict emissions test.

Dman:

Volvo Bricks require high octane gas(95). Since 1983 the Brick has had a knock sensor in the engine to alter the timing when a knock is heard. That is why you hear only one, your knock sensor is working well. I recently tried to use lower octane during the recent gas crisis, and in addition to the knock I felt a loss of performance at the high end. So even if damage is prevented by the knock sensor (and I am not sure it is) I did not feel it was worth the savings in gas price.

lenk

I thought the non turbo cars were good on regular gas.

Good, yes, generally. Then there's better, & best... I put regular in my 740 most of the time, every few tanks I'll go with supreme & it seems a bit snappier when really pushed but otherwise not much difference. I just use it to help keep things clean. The turbo does suffer with regular, especially the '84, no knock sensor on k-jet so it will no doubt blow up if I run regular & drive it hard - even with mid-grade it'll knock under boost. A lot of that is tuning too, though, any Volvo can be set up to run on regular at the expense of some top-end power and economy.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina