Toyota Repair: 90 Toyota Corolla AllTrac fuel injection problem, electronic fuel injection, toyota corolla

Question
My 90 Toyota Corolla AllTrac (4A-FE) has what I think is an electronic fuel injection problem. First, the vehicle has 250K miles and is on it's second (used) engine. Usually a smooth car, yesterday it suddenly started running roughly at low speeds / rpms, but smoothed out somewhat at rpms above 2,500 or 3,000 - though not completely. I felt all the injectors and found the #2 cyl one was not clicking at all, the other 3 were. I replaced it with a 'known good' (but used) one I had around from replacing the engine. Still no clicking and the symptoms remained. I did a compression check (165-170 in all 4 cyl) then replaced the plugs (the #2 was slightly browner than the rest, although all looked OK, they had ~25K miles on them). Still the same. I disconnected the electric connection from all 4 injectors and connected each again, by itself and one-at-a-time, engine almost 'caught' on each of the other 3, but nothing on the #2 cyl. I checked the voltage at each injector connector while cranking, all 4 were ~10 V (although this is too crude a measurement to detect any individual pulses). I'm at a loss as to what other diagnostic checks I can do - I'm afraid it might be the ECU, but there is no 'Check Engine' light. (I'm a former mechanic, but don't have a lot of sophisticated equipment). Do you have any ideas what else I could look for?

Answer
Hello, what you need to do is to check for pulse voltage across both terminals of the injector connector, one side should have near battery voltage constantly the other terminal is grounded on/off by the computer, you are looking for this on/off pulse when cranking the engine or while it's running, you can use a testlight but a special noid light that plugs directly into the connector is best, let me know if you have this voltage pulse.