Does anyone know what causes the engine knock/rattle sound when you are accelerating? I used to only hear it when using 87 octane fuel. After a few years it started knocking when using 89 but now I'm starting to hear it with 92 octane. The engine runs fine except for the knocking while accelerating. Is there a way to fix this?

Thanks for any advice.

D'Arda
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1989 740GL (244K)

My guess would be that there's a buildup of carbon in your combustion chambers; this can be fixed by carefully feeding water(or some fancy proprietary solvent) into the intake while the engine's running. This is probably best left to a professional.
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Jim McDonald

Find some jobber in your area that has a motor vac unit, machine will hook up to your fuel delivery system at the fuel rails and cleanse the entire system.
Fuel injectors,valves,combustion chambers and even your o2 sensor.
Cost anywhere from 60 to a hundred bucks depending where yo are.
Good Luck
Poolman