Ignition Code And Wiring Repair - Mechanic Live Chat

Question: P2302 - ignition failure coil A secondary circuit. Wwe replaced the PCM and coil. Resistance is 0 ohms on negative pulse wire from PCM to coil. Car runs but poorly. What else to do.?
 Mechanic: Make, model, engine size please? Is the resistance 0 ohms or open?

Dodge, 2005 Grand Caravan, 3.8L. I got 0 ohms on all 3 negative pulse wire from PCM. And when I backprobe at PCM I get pulse 2 wires during crank and run state. But the wire feeding coil A has no pulse.
 Hmm. Not really sure, don't have much experience with particular vehicle electrical systems operation.

If there is no pulse with test light on backprobe at PCM, does it make any sense to run a new wire from PCM to coil? If so, how does one do that? What is needed to get wire inserted into the pin positions?
 No. The PCM is what sends the pulse. So, if there ois no pulse coming out of the computer then replacing a wire will have no effect on the circuit. Either the coputer is not sending the signal because of an internal failure or something else is not tell the PCM to do it.

Theory from a different mechanic was also that I might have a short to ground of some kind in the harness that was causing PCM to not send negative pulse on the wire to Coil A. Seems really, really odd that replacement PCM would have same problem on exactly the same wire.
 If shorted to ground you can check that by doing resistance check from wire to a knon good ground. Resistance should be mega ohms or a reading of OL on the meter, depending on what kind you are using. But it must be disconnected from coil and PCM. Yes, i would not think same problem with another PCM.

But I did the resistance check with disconnection from coil and PCM. That is when I determined, checking each wire at least twice, that resistance is 0. That indicates that there is not short to power or ground also? I don't know.
 No, that just indicates the wires is not broken from end to end. Zero resistance means that it is a perfect continuity circuit. The exact opposite of an open circuit.

Do you think it's a possibility that there could still be a short somewhere in harness that is causing PCM to not send pulse?
 Yes. The wire could be shorted to ground or to another wire inside the harness. Take it apart and physically clook at them.

Any suggested links to electrical tutorials on how to do that? Or on properly replacing negative pulse wire to the connectors? You could recommend slicing open the harness to try to get wires apart to see where the short might be? Or is it hopeless with more tools than a test light and very basic meter?
 First check resistance to ground. Should be 0 ohms. If O, then it is not shorted to ground, but that does not test for short to another wire. You would have to open harness and follow wire to check that. You could always just cut wire at each end and crimp on a new one from PCM to coil.

Ah. I suppose parts store could have stuff for splice. I don't have it on hand. I'm inclined to that at this point. Do you think a short on some other wire in the harness might be causing issue of no actual pulse coming from PCM?
 Yes, it could. But it could also cause a problem on the circuit of the wire it may be shorted to.

I appreciate the pointers. I'll try to get you a tip/donation. I see its done via Paypal.
 Thank you and good luck.