Well, it looks like the dieseling problem on my 427 C/O is solved.
I rechecked the timing mark on my pulley and damper and found it to be ok!
Just to inform you, when I put the engine together I found that it had either a wrong timing mark pointer or that it had been installed backwards.
I found the correct TDC and bent the marker so as to show 0º TDC.
I am using a super-duper dial-in advance electronic timing light and thought that the timing was spot on.
Well no, it wasn't.
I had set the advance with the electronic timing light at 14º, so that I could have the butterflys pretty closed but still get a decent idle. Dieseling still ocurred.
I took a 30 year old RAC induction timing light I had laying around in the junk box and hooked it up between spark plug #1 and the plug wire .
Since mine is an MSD 6AL ignition, the multiple sparks it produces generate multiple flashes which are not easy to distinguish with an old induction timing light. But looking at the very first flash mark I could see the timing was actually 0º, so no advance at all.
I adjusted the timing to the correct 12º advance with the RAC light and in order to get an idle of 700rpm I had to back off the idle screw almost one full turn.
The butterflys are now almost closed, (idle screw is now just 3/4 turns in),
the idle is now really nice and smooth (even at 700rpm !) and during the two dozen times I switched off the engine no dieseling ocurred
Resumee:
1.Some electronic dial-in timing lights are no good with MSD multiple spark electronic ignition.
2. The timing mark on your pulley or timing pointer may be wrong, and your timing may be way off.
I hope this gives all the Dieseling sufferers some extra comfort and hopefully also a definitive fix.
