ok, an update.

firstly: in some of the cars, the upper bolt on the tensioner is a recessed hex. so... that was easy once i figured it out. so... put it all back together, and now when timing it to 7 BTDC, the distributor adjustment is now perfectly centered! (before it was off to one side). so cam timing was definitely off by a tooth, and possibly had been run for 5 years that way, with distributor timing used to counteract. what damage could that cause?

however! this fix resulted in little or no change in the symptoms (!).

i decided to check the spark plugs and do compression test. all the plugs are between 160 and 170 psi dry (though my gauge might read high). however, they're also all dry carbon black -- which is new (when i swapped new plugs in at the beginning of all this, they looked grey-normal). so -- running rich! that also makes sense of the backfires, right?

well, that seems to confirm it's not the fuel pump, but maybe the regulator is keeping pressure high? so i decided to swap regulator with parts car.

however! they say you have to remove the air intake plenum. i tried to remove without doing so, and *almost* could, but could not remove the center bolt entirely. *sigh*. the plenum is a real PITA to take off and put on. some hints: there's 4 bolts and two studs for the mating surface. there's a 14mm bolt underneath on the stay. there's a hidden stay on the inside, above the fuel rail. you have to undo both the bottom bolt (angle wrench required imho) and ALSO the top bolt into the plenum, which is much easier with a long extension straight underneath the TB/rubber connector. then there's a coolant hose underneath, that you really can't reach till you take the plenum off. also, the plenum is designed with a little ridge next to the bottom stay that means have to kind of force it (with a soft prybar) off and on the studs. *sigh*

well, after hours of puzzling through all that (and cleaning the gasket off, etc.) -- the swapped regulator resulted in ... not much difference.

(the one advantage is that i could at least tell that the EGR is a bit dirty but not plugged at all.)

what the heck?

just because, i opened the ECU. no sign of swollen capacitors.

what else could it be? i might try the coil again, but... as i said, already swapped it before with no change.

could this be the O2 sensor? it's running the one from the donor '95, that has the same harness and per rockauto means it's federal emissions, same part. again, that car didn't have this problem...

finally, here's the weirdest thing -- just on a lark, i connected those two harnesses on the passenger side of the firewall, that i believe connect to the tachometer when installed (i don't have one), and the vehicle suddenly behaved ... better. ie. i could rev easily from start. i took it for a test drive, and it was a little improved, like i could drive uphill at 30mph not 15 mph... but still bogging and backfiring. and by the time i got back, seemed to be back to the worse-normal.

what's going on? does that tach connector go to the computer somewhere? is maybe the computer at fault, but invisibly?

any ideas for how to systematically troubleshoot this, it's driving me a bit nuts.

thanks!!