The “spark but no injector pulse” is a classic Marelli ignition problem.
The only certain way to test the Position and Speed sensors and their associated wiring is with an oscilloscope at the ignition computer, located in the passenger side footwell. This will confirm that the signal is making it all the way from the sensor to the ignition computer. From there, the ignition computer must send a pulse to the lucas injection computer (aka ECU) in the trunk. Based on your description it’s highly likely that the Position sensor is bad. I would suggest three options:
- Track down the crappy little white wire in the wiring harness on the left (from drivers seat) side of the fuel rail. It has a connector near the center of the fuel rail which connects the Position sensor to the rest of the harness. Disconnect and clean and reconnect. Known weak point.
- I agree with Paul and Bob. Buy a position and speed sensor and swap them out. If that turns out to not be the problem, keep the extra sensors in the trunk. One should not drive around in a Marelli car without a spare, and the PN is the same for the Speed and Position sensors. If you solve the problem without a new sensor buy a spare anyway.
- Buy a cheap digital oscilloscope (less than $150) and do the test per the Repair Operations Manual (ROM). Mine is a Vellman HPS10, but anything similar will work. In the ROM Be sure you are looking in the “supplement” for 89 1/2 and newer cars. This will also allow you to confirm the output of the ignition computer to the fuel injection computer in the trunk (which it sounds like you’ve already done per Bywater.) All the pin outs for the computer are called out in the ROM.
DO NOT cross-connect the sensors as you suggested in your reply to Bob… he was suggesting that you remove the two sensors completely and re-install each in the other location. If you are going to that pain just buy two new ones and replace them, the fishing of the harness wires is a bit fiddly.
The sensors don’t generate anywhere near 10 volts so not surprising they are not registering on your meter.
Regardless of any of the above, I strongly suggest referring to the ROM. It is very clear on how all this stuff works on the Marelli car.
My .02, worth everything you paid for it! Good Luck!