Detonation at idle

George M. Dailey gmd at tecinfo.com
Fri Mar 1 23:25:46 GMT 1996


At 12:09 PM 3/1/96 +0500, you wrote:
>"Should there be a very slight detection of detonation (knock) at idle
> with engine hot?"
>
>No. You need ridiculous timing advace to knock at idle. You are 
>probably(and unfortunately) hearing a mechanical problem such as 
>piston slap or bad lifters.
>

======================================================
On my last 350 TBI engine, I noticed that if the engine was hot (190 deg. F)
and the inlet air was hot, if you advanced the timeing you would hear what
sounded like detonation. You did not have to go far! When the timeing was
retarded the sounds would go away. Let me also add that you don't hear the
sound just off idle and it's around the same sound level of the injectors
clicks. The hood must be up to even hear the sounds.  When under full
throttle, I'm sure that it's slightly detonating. I'm not sure if the ECM is
detecting 100% of the detanation. I once herd that the GM ESC will rattle
just a little, some times, at full load. I've herd a TBI rattle with the
nock sensor disconnected at full load. My TPI is no way near this. BTW
79,000 miles on the clock, car was driven every day, auh 'aggressively' but
well pampered as far as maintenance is concerned. It kissed another car.

Thanks for your input Dudes.

GMD




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