Rattle Rattle Rattle

[BumbleBeat]

I FINALLY have news. The noise detector confirmed the noise coming from the engine. It wasn't very useful for narrowing down beyond that, but at least I can rule out drivetrain. Early on in diagnosing this I retarded the timing quite a bit to test for pre-ignition and the noise didn't change. I retarded it again today, apparently more than last time, because it got quieter, and still had good power, which surprised me. If a little is good, a lot is better, so I dialed the distributor as far as it would go and the noise is gone, or nearly so. There's some strangeness here. I had the timing dead on. Jumpered the connector, strobed the 20BTDC mark at 1200rpm, it's pretty routine. In the current max-retard condition, the engine light is on and the car can barely pull itself at low rpm, no surprises there. But at high rpm it drives like normal. It seems like it's advancing way too much. The other thought is that it's running way too lean at high rpm, which could also induce pre-ignition. Recall that the knock only happens under a high speed load; no noise with clutch in or sitting in the driveway revved to the moon. I'm beginning to think this mystery is an ECU problem. Make sense, since ECUs are a complete mystery to me. Any thoughts Beat Genius Steve_M? Greenscale, have you tried retarding the ignition way forward?