I've got an 89 2wd pickup with the 22r motor in it and it has gradually developed a problem. I commute about 120 miles a day round trip though gently rolling terrain and my truck has gradually begun to detonate more and more over the past 5 months when climbing slight hills at 70 mph, the kind that require a slight application of throttle to maintain speed. About 2 months ago I retarded the timing by feel until it stopped detonating, and continued commuting... guess what came back, so I retarded it some more...it still does it. I finally got my timing light out and the timing was about 5 degrees AFTER TDC, so for yucks and grins, I set it to 8 deg BTDC, now it detonates damn near all the time. I'm suspicious that I've developed a weak or broken spring in the vacuum advance. The vac advance is the dual can type and the detonation only occurs when the engine is hot (that's when the innermost can is activated) Anyone have any thoughts on this? cuz it's annoying the stew out of me!