Re: Pre-ignition knocking (e21 315) (archive)

She is run 205 500 km.
She does not consume oil (not much anyway).
I changed to octane 98 and the problem seemed to go away.
Is this very bad to the engine? Can I live with it for 2 years? (afterwhich the life of this car runs out and is due for scrap)

: How many miles? Does she burn oil?

: More than likely, you have bad carbon deposits on the exhaust, and possibly intake valves. These deposits will glow red from engine heat, and ignite the fuel/air mixture after the ignition has been shut down. Do a compression leak-down test to check condition of valves. Listen for escaping air in the intake manifold, or exhaust manifold. The side that leaks probably has carbon deposits causing the problem.

: Short term solution => higher octane gas
: Long term solution => valve job with decarbonization

: By the way, check and make sure engine is running in the right direction when it "deisels". I had a car that quickly self destructed from "deiseling", but would run backwards, i.e., no oil pressure. It was an automatic, so the only way I could stop it was to shove a rag in the tailpipe! A real show stopper.
: : Hello,

: : I tried using octane 92 for my '82 4 cylinder 315. When I switch off the engine, she refuses to quit and the engine will "rock" for about 5 to 10 seconds.

: : I just changed to Octane 95 unleaded. This seems to cure the problem. Anyone out there has similar experience?

: : Should I use lead additives? I just bought the car for 2 months and don't know the history of the valve seats.

: : Thanks,
: : Hock Ann
: : Singapore

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