Pre-ignition Detonation

[Mopar]

Have a stock 89 2.0 5-speed low miles in outstanding condition. Engine runs very good except it really pings (preignition) at multiple throttle positions when hot. 93 octane gas helps a little. Ethanol free versus E10 gas makes no difference (E10 caused enleanment might worsen detonation). Timing is to spec and Autolite plugs are what the manual calls for (plugs look good - not like its running excessively hot). Engine appears to be running normal temp (needles always "in the middle" of the gauge). Any ideas? Its been a long time since I've tinkered with one of these "final days" of carbed smog engines, remembering sometimes the poorly controlled red-hot EGR gasses are doing more heating than cooling of the combustion chamber. Ideas on getting rid of knock? Block EGR and throw a Weber on it?

Thanks

[pennyman1]

Run some Redline fuel system cleaner through it - 1 bottle to full tank of gas. Also clean out the egr valve and passages to get rid of the carbon buildup. The carbon buildup is what is causing the detonation.

[geezer101]

I've heard complaints about what plug to use in which engine. Maybe use Denso or NGK plugs as an alternative. You could try a different approach to setting your ignition timing (you got nothing to lose and if it doesn't seem to help you can go back to conventional ignition tuning). Start the engine and get a friend to hold the rpm's @ 2000, then undo the distributor retaining nut and swing the distributor back and forth until you hit a 'sweet' spot and the rpm's jump slightly by themselves. Retard the distributor a touch and lock it up (this will compensate for the lack of engine vacuum advance from not being under load). This should set the ignition to fire at it's optimal rpm. I've gone as far as regapping the plugs 0.5mm under the standard gap setting so it retains tune for longer. I get engine 'ping' from running regular fuel but switching to premium eliminated it.

[Mopar]

Most of the detonations seems to have been caused by a stuck heat stove duct (valve on the air cleaner sintake snout). Was constantly sucking air from the exhaust manifold regardless of engine temp. Fixed and pinging is way down now. Also ran shock treatment of Chevron Techron (PEA) through it.