I have a 2005 3.7 Liberty & I have a code for # 4 injector . I have definitely narrowed the problem down to no ground signal from the pcm for that injector . I traced the wire from the injector to the pcm connector , bared a small spot in the wire just outside the pcm connector & there is no ground signal coming out of the pcm on that wire .
Does this definitely condemn the pcm or could something else cause the pcm to not send out a signal for one injector only ? I suppose it's possible , but I think highly unlikely that the problem could be in the pcm connector itself . I have had it unplugged & the connector & pin both look ok .

Have you done continuity checks through the harness to make sure there isnt an open circuit somewhere?
You should also test resistance through the injector.

_________________
U.S. Army Retired

I have verified the injector is good & the wire that is supposed to provide power to the injector is providing power . I have also verified continuity on the ground wire from the injector to the pcm . The pcm is not providing a ground to that wire . If I understand correctly the camshaft position sensor provides a signal to the pcm when to provide the ground signal to fire each injector . All 5 other injectors are receiving this ground signal from the pcm , just not # 4 . I don't know if it's possible for a faulty sensor to just skip one injector .

You are proably going to need to use a fuel injector test light (a.k.a noid light)
It will help you identify if the signal is getting to the injector.
You can also try swapping the #4 injector with another one. If the code moves to the other cylinder then you know the problem is with the injector. If the code stays with number 4 then you know that its the wiring.

_________________
U.S. Army Retired

Please reread my posts , { there is no ground signal coming out of the pcm for injector # 4 } .

If you are absolutely sure of that then you will need a new PCM.
I would want to be absolutely sure that its NOT a wiring problem before I went through the expense of replacing the PCM.

The PCM controls each injector individually.
If the injector is not receiving the pulse signal then the the problem is within the PCM.
The injector is grounded through the PCm by way of a transistor.
The PCM turns that transistor on and off, creating the injector pulse, turning the injector on and off at the appropriate times.
This is difficult the test with a volt-ohm meter because the engine has to be cranking or running for the transistor to be active. And the pulses can be so fast that you may not be able to see it with a meter. This is why I suggested the noid light.

_________________
U.S. Army Retired

I already used a noid light in addition to verifying power on one wire & continuity on the ground wire to the PCM . The noid light doesn't flash on # 4 but does on other injectors .

Good. Looks like you have identified the problem then.

Just to be safe, I would do a resistance test on the #4 injector and compare that to some of the other injectors.
If resistance is too low, current through the injector circuit would be too high and might be what killed the PCM.
Or maybe it was just cheap Chinese components.

_________________
U.S. Army Retired

Did that & tested good , swapped it with another cylinder anyway & problem stayed with # 4 .