I have an issue that maybe some of you can help with.

1987 244 with unknown mileage. When I crack the throttle quickly (car parked), the engine bogs down real bad and will backfire through the intake. Slowly raise the throttle and the engine runs nicely.

Idles great and runs clean. Car starts easily, even at 20 degrees. Compression is 175 across the board. Fuel pressure tests are all good (Pumps replaced about two years ago). New fuel filter, amm, plugs, wires, cap, rotor.

Verified that there are no vacuum leaks anywhere, including the brake booster.

Fuel pressure regulator is functioning properly (bumps from 30-40 psi when disconnected).

I have monitored the O2 sensor signal and injector duty cycle and everything looks great. When I crack the throttle, the duty cycle will increase sharply and the O2 sensor responds throughout the entire speed range. TPS, coolant temp sensor, etc. all check good. Timing belt is recent and cam timing is dead on (I checked again last night. Alternator voltage is good. Overall, I cannot find anything wrong with the injection system. I even tried a couple different ECUs with no change.

There are two possibilities, but I need more opinions before I spend more money.

Injectors could be marginal. Perhaps they are not flowing enough for max load. If they were partially clogged, I would expect a greater duration at idle to compensate. I am getting about 5% duty cycle at idle when hot.

I get no change in advance when I remove/apply vacuum at the diaphragm on the ignition ECU. I know that is not normal, but I have run 240s with that port blocked before and never noticed a problem.

Is the ignition supposed to advance, or retard, on acceleration. The timing does advance with engine speed, so that part works. If it is supposed to retard, how would that make it any better (other than for emissions purposes)?

What do you think?

Anthony