I have a 91 RS 305 with TBI.
Its making somekind of rattling (or pinging?) noise from the engine. But mainly under 45 mph, when the engine is about at 1000 to 1500 rpm.
I'm not sure if this could be detonation. What exaclty is detonation anyways, I hear it comes from advanced timing and all, but what exactly is it, and how is it bad for your engine?
I also have a code 32 (EGR) coming up on me. Could these be related?
Please help, thanks

 

Detonation is an uneven and premature burn of your A/F mixture in the combustion chamber, In essence the brute force of the explosion happens before your piston has reached the top (to soon) and the momentum and force of the other 7 cylinders is fighting against that one to get it over. It will sound like a diesel engine (some describe it to sound like marbles?) and its usually most noticable under load, WOT, or higher RPM's. Its unusual to get knock while idling or in park, and at lower rpms unless your timing is severly off.

Get out your timing light, set your base timing to 0, then go drive, if you notice any difference at all in the sound then you know its timing related, if nothing changes look elsewhere.

 

TPI_ROC covered the first part of the question. As for the EGR, yes, an inoperative EGR system will contribute to this detonation, especially while cruising at 1,500 RPM - right when the EGR should be opening and controlling chamber temperatures.