After basically two years of driving around at less than half throttle to avoid detonation (quite severe on hills, and downright rattling when it downshifts going up a hill), as well as attempting various fixes to try and stop it, which included the following:
- new plugs/wires
- premium fuel for the last 2 years
- low temp thermostat
- fuel injector cleaner
- engine analysis computer last month shows NO CODES
I finally thought, "well, it's an 8 year old engine, maybe the timing's just drifted out a bit" so I took the doghouse off to get at the engine, scratched a fine mark on the block for the distributor position before I started, loosened the distributor adjustment bolt a bit, started it up, got it to operating temp, and took off down the road.
Once I got to an empty back road, I put the throttle down to the point where it starts knocking quite badly, and then reached down and turned the distributor very slowly one direction, and then another, hoping that I would retard the spark timing to the point that it would stop.
It didn't seem to make any difference. I could turn it to the point that the engine quit running in either direction, but the knocking was still there under moderate power. I could only make it worse. I couldn't find any point that seemed to lessen it or make it go away. After maybe 30 seconds of this, I gave up and set the distributor back to where it was before I started, on the mark I'd made before loosening it.
All seemed well, I took the van on a short 15 mile trip later in the day, driving as I had for the last two years, with very little throttle, and the engine behaved okay.
Today, I went to drive somewhere, and when I got on the back road, the engine started to make some very odd sounds, almost like a rock being shaken in a steel can. Detonation was still there if I put the throttle down. I aborted the trip and drove it home very gingerly, hardly putting in any throttle at all.
It's got me quite worried. Then I looked up an old post I made in this group back in 2003, where a respondent actually warned never to do the very thing I did:
Feeling a bit of a fool at the moment - what's the worst damage I could have done, anyway? Made the timing worse, certainly.
I wonder if a new distributor cap and rotor is all it needs?