My stock 96 3800 series II */C started detonating about a week ago. With no codes set. I looked at the timing and it was at 20 deg at idle and 38 deg at wot (BTDC), (I believe it should be at 15 deg at idle and 20 Deg at wot ?) . I have changed the TPS,Knock sensor module in PCM,and tried two other Pcm'* that did the same thing. I then relized that if the pcm dosen't control the timing, that the Ignition control module would default to a 10 deg btdc setting for all engine speeds. So I cut the wire to the ICM from the PCM and sure enough the timing went to the default of 10 deg Btdc, with no detonation at all . Anyone ever had this happen or know what to do. Wonder if a case learn would help ? Thanks, Chris

Are you running premium gas?

I can tell you it is not the gas. It is supposed to run under perfect conditions 17 degrees ignition timing at WOT, but usually about 15 degrres. I have never heard of this happening before, and I don't know what to do about it. As much as I hate to suggest something like this, but maybe bring it into the dealer and have them fix it.

From what you have listed, I would replace the ICM. You have tried 2 different PCM'*, so a case learn won't give you anything. Since you cut the wire from the ICM and the trouble stopped, I'd say that the ICM is sending faulty info to the PCM.

I do run 92 octane, and I guess I will try to find an ICM at the junkyard. Unless someone knows where to buy other than the Dealer ?