Hello all,
I have a no start issue on a 1985 T16 LH2.2. It's not starting because there's no fuel, because the injectors aren't injecting, and the injectors aren't injecting because the ECM is not pulling down the fuel pump relay. More specifically, Pin 17 of the ECM is not sending a ground signal to the fuel pump relay via the purple wire to Pin 85 of the fuel pump relay. Both relays undoubtedly work, and the pump relay has power from the system relay when the key is on, it's just not getting activated by the ECM. I have another supposedly good ECU that I plugged in and got the same issue. This to me indicates the ECMs aren't likely the problem, so much as some signal that the ECM is or isn't getting that is telling it not to fire the injectors.
I know in order to activate the injectors, the ECM needs a cranking signal, which I believe it's getting because Pin 1 of the ECM (the engine speed signal input) gets 2-3 VAC when the motor is cranked, which is what the Bentley specifies. Furthermore, I pulled the cable going from the ignition coil to the distributor and held it close to the block while the engine was cranked and saw spark - to my understanding, this rules out a bad Hall sensor, correct? Are there any additional tests I can do to make absolutely certain the ECM is getting the cranking signal?
The other issue that I know might prevent the ECM from activating the fuel pump relay is a wide-open throttle signal, which would be a ground signal at Pin 12. There is not a ground signal at Pin 12, which to me rules out a WOT signal snubbing the ECM.
Is there something else I'm missing that would cause this issue? I have been troubleshooting this for a long time, and I'm pretty sure I've traced every wire in the ECM loom, and it feels like I've exhausted every troubleshooting recommendation in the Bentley (every other ECM pin test in the Bentley comes back good) or that I can find online, but obviously I'm still missing something. Does anybody have any ideas where I can go next with this thing? I am utterly stumped. Any suggestions anybody has would be greatly appreciated! Thank you!
I have a no start issue on a 1985 T16 LH2.2. It's not starting because there's no fuel, because the injectors aren't injecting, and the injectors aren't injecting because the ECM is not pulling down the fuel pump relay. More specifically, Pin 17 of the ECM is not sending a ground signal to the fuel pump relay via the purple wire to Pin 85 of the fuel pump relay. Both relays undoubtedly work, and the pump relay has power from the system relay when the key is on, it's just not getting activated by the ECM. I have another supposedly good ECU that I plugged in and got the same issue. This to me indicates the ECMs aren't likely the problem, so much as some signal that the ECM is or isn't getting that is telling it not to fire the injectors.
I know in order to activate the injectors, the ECM needs a cranking signal, which I believe it's getting because Pin 1 of the ECM (the engine speed signal input) gets 2-3 VAC when the motor is cranked, which is what the Bentley specifies. Furthermore, I pulled the cable going from the ignition coil to the distributor and held it close to the block while the engine was cranked and saw spark - to my understanding, this rules out a bad Hall sensor, correct? Are there any additional tests I can do to make absolutely certain the ECM is getting the cranking signal?
The other issue that I know might prevent the ECM from activating the fuel pump relay is a wide-open throttle signal, which would be a ground signal at Pin 12. There is not a ground signal at Pin 12, which to me rules out a WOT signal snubbing the ECM.
Is there something else I'm missing that would cause this issue? I have been troubleshooting this for a long time, and I'm pretty sure I've traced every wire in the ECM loom, and it feels like I've exhausted every troubleshooting recommendation in the Bentley (every other ECM pin test in the Bentley comes back good) or that I can find online, but obviously I'm still missing something. Does anybody have any ideas where I can go next with this thing? I am utterly stumped. Any suggestions anybody has would be greatly appreciated! Thank you!