Hi Brains Trust,

My '91 2 door EX is detonating (hope that's the correct term, I'm Australian) quite badly when the engine is cold/under load. I had a mechanic check the timing recently, and I've also tried adjusting the timing a little by ear and it still does it. Just wanting some suggestions for what it might be? Spark plugs?

Thanks!
Carl

 

I would definitely take care of the maintenance items first. When were the spark plugs, distributor cap, distributor rotor, and air filter last changed?

 

Unusual for this engine to have detonation.

Reasons for detonation; timing advanced too much, combustion deposits, wrong spark plugs, lack of exhaust gas diliution (should not be a factor w/ a cold engine, only fully warmed), compression too high (special pistons or heads),

Are you sure the noise is detonation? A rattling clatter could arise from valves, but not quite the same noise.

good luck