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In Reply to: Pre-ignition knocking (e21 315) posted by Hock Ann on March 09, 2000 at 21:50:15:
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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