No pulse in only #6 injector

[Robert Deringer]

What might be a cause of no pulse to only one injector on my 92 3.0 cyl#6? I've checked it with a noid light and have no electrical pulse. All others are working. Any thoughts?

 

[Robert Deringer]

To add to this, I get trouble codes 212 and 543

 

[adsm08]

Broken wire.

You have a batch fire system, so two sets of pulses, and each set fires 3 injectors. All 6 draw power from a common bus. If only one injector has no pulse then you have a broken wire going to that injector. You need to figure out if it lacks power or ground and then fix the appropriate wire.

 

[Robert Deringer]

Broken wire.

You have a batch fire system, so two sets of pulses, and each set fires 3 injectors. All 6 draw power from a common bus. If only one injector has no pulse then you have a broken wire going to that injector. You need to figure out if it lacks power or ground and then fix the appropriate wire.

Thank you! Ok, with a multi meter I get full battery voltage (continuous) at the red wire too injector. I then checked ohms to ground on the other wire (assuming that needs to ground) and there is no continuity, completely open. I do get 2 trouble codes: 212-ignition module circuit failure/SPOUT circuit grounded, and 543- fuel pump circuit open; battery to pcm. Though truck does run still on 5 cylinders

 

[adsm08]

Ignore those codes for now.

You can't test the injector ground with a multi meter. It isn't a constant like the power. The PCM pulses the ground for the injectors based on signals from the engine positions sensor(s), and so it won't show a ground with the engine off.

The best way to test it is with a noid light, as you have already done, and then when a bad pulse is found test for power, as you have also already done. I'd say its time to overlay the ground side from the #6 plug back to the splice in the harness. Best to connect a little up stream of the original splice if you can, as that is likely to be where the problem is.

 

[Robert Deringer]

Ignore those codes for now.

You can't test the injector ground with a multi meter. It isn't a constant like the power. The PCM pulses the ground for the injectors based on signals from the engine positions sensor(s), and so it won't show a ground with the engine off.

The best way to test it is with a noid light, as you have already done, and then when a bad pulse is found test for power, as you have also already done. I'd say its time to overlay the ground side from the #6 plug back to the splice in the harness. Best to connect a little up stream of the original splice if you can, as that is likely to be where the problem is.

Thanks again for your help. When I was testing for ground continuity I was doing it with the engine running. In any case, here is what I now know. The ground side of the 2 injector wires is green/orange stripe. I've now physically traced it back to the computer. I have continuity from the injector plug to the computer plug under dash passenger side kick panel. I do see signs that the computer may have gotten wet from rain leaking through rusted door/windshield post. I regularly have puddles on floor mats if left out in rain, so I'm aware it leaked. I see some rust streaks and signs of water on computer body. Could the computer be causing this if compromised by moisture. This is just my weekend beater and loaner truck. Had loaned it to a friend and I came back like this. Likely was left out in heavy rain.

 

[adsm08]

It could be. I know the 2.9 and 4.0 were both batch fired injectors that year, and I don't see that the 3.0 is likely to be very different, but I don't have the diagrams for a 92, so I can't say for sure.

I would also load test the wire. Unplug all injectors, unplug the computer, and use a paper clip or something to jumper power from the injector+ to the injector - and then see if you can use the power at the PCM connector to light a light bulb.

 

[Robert Deringer]

It could be. I know the 2.9 and 4.0 were both batch fired injectors that year, and I don't see that the 3.0 is likely to be very different, but I don't have the diagrams for a 92, so I can't say for sure.

I would also load test the wire. Unplug all injectors, unplug the computer, and use a paper clip or something to jumper power from the injector+ to the injector - and then see if you can use the power at the PCM connector to light a light bulb.

Ok, I had to run out for a test light. I did as you suggested, jumped the wires at the injector plug, and I do get a light at the terminal end at the computer module.

 

[adsm08]

Ok, I had to run out for a test light. I did as you suggested, jumped the wires at the injector plug, and I do get a light at the terminal end at the computer module.

The circuit works and the issue must be at the computer then.

 

[Robert Deringer]

					The circuit works and the issue must be at the computer then. The circuit works and the issue must be at the computer then. adsm08, thanks so much for all your help.