The combo: '91 Sub TBI 350 700R 3.73 285/75/16 The caveat: This is the first computer controled engine I've had to fix. I'm also tone deaf so hearing very mild detonation hasn't happened in the past. The complaint: Has recently started detonating on fuel it used to be happy with. No obvious symptoms of a vacuum leak. Idle speed is about right. No whistling at idle. No real loss of power. Going to WOT sometimes cures it, sometimes not immediately - fades away. Downshifting ditto, but usually does. Don't yet have the info needed to pull codes, if any. Some recent history: Chasing the Vegas to Reno race it developed a misfire under load. In the Circus-Circus parking lot in Reno we threw plugs (.035"), wires, cap, rotor, & fuel filter at it. Misfire was coil wire leaking thru a rub'd thru point. Had Bosch 4 ground electrode plugs in it (eewww!), now has 'normal' AC's. The obvious: unplug wire & check base timing; will happen this afternoon. What else?