Hello there!


To start off.. I have a 1996 Jeep Cherokee, Auto, 4x4, pretty much bone stock..


My XJ is coming up with the code P0204 (Injector 4 circuit malfunction) and you can definitely tell its only running on 5 out of 6 injectors... I have replaced the injector with a new OEM injector, I have also replaced the PCM with a used (but same part number) PCM, and the wiring all looks pretty good. When I put in the new injector, it made no difference. When I put in the used PCM, it worked fine for a little while then it started acting up again and throwing the same code. I have looked through all the wiring and it all seems to be just fine. I have also checked the wire circuit with a volt meter and there isn't any more resistance than any of the other injector wires, I checked the whole circuit, as well as bypassed the positive and negative with a different wire and connections. When I put a noid light in the injector plug there is no pulse. Also, when I check the power from the PCM, its dead.


Essentially, I am getting no power signals from the PCM to this one injector (fuel injector 4).


I did NOT flash this PCM after installing, though this jeep is running the same exact way as it did with the old PCM. The dealership told me I HAD to get it reflashed, though I think they are trying to just squeeze my hard earned money out of me.. and my trustworthy mechanic said as long as it starts and runs the same way that it did before that I did not need to flash this PCM..


I also am aware that there was a recall on the software on these PCMs and that they needed to be reflashed at that point with new software. I need to do a little bit more digging, but at this point I don't know exactly why they were recalled and what issues they had back then..


I just need some help figuring out what to do next. I feel like this PCM just coincidentally has the same exact issue on the same exact injector or the wiring is messed up where the pigtail for this particular plug goes up into the wire harness by the valve cover, and where the wiring has gotten stiff and brittle from the engine heat..


Thanks in advance for your input and sorry for the long and detailed post!

 

Check The wiring, when you switch the ignition on the injectors get constant power. The pcm sends a ground pulse to the injectors.

 

You need to determine if there is voltage on the positive side of the injector. There should be constant voltage, the ground is switched on and off in order for the injector to function.

 

Check voltage on another plug then check one for missing cylinder . See if there equal then check for ground signal to injector sounds like bad wire . When you installed new ecm it made a connection from moving harness around.

 

Sounds like a problem with the PCM connector or wiring.

The fuel injector should receive 12V from the ASD relay when the PCM thinks it's okay to run the engine (when the CKP/CPS signal is good the PCM grounds the ASD relay control side). This might be a little akward to verify but you can just check for continuity between the 12V pins of two injectors.

The injectors are operated by the PCM grounding them out. Like freegdr said chances are the issue lives with the PCM connector. I'd start by cleaning the connections and tweaking all the pins with a dental pick. They're basically springs and can wear out. For some ideas look up cruiser54's Mostly Renix Tips and check out C101 refresh. Same concept.

 

Here's a diagram of the '95 fuel injector circuit. I don't have the '96 diagrams.

If you have only one connector on your PCM this diagram should match. If you have three connectors on your PCM that's like a '97 PCM configuration. I have a diagram of the '97 circuit if you need it.

The wire color codes are the same for the '95 and the '97 so the '96 should fall in there as well.

The thing to do is read the resistance of the PCM fuel injector driver wire from the PCM connector to the fuel injector to see if it's open or has high resistance (over 5 Ohms).

To check for power at the fuel injector, pull the connector off and connect your voltmeter ground probe to the battery negative post and probe the injector connector pin cavity with the Dark Green/Orange tracer wire with the (+) probe while the engine is running. You should see 12 VDC if the circuit to the ASD is intact.

 

I checked the connector to the PCM and it testes okay, though I have not tried to readjust any connections. I have checked all the circuits with a volt meter and they all seem to be okay as well. The only thing that I've come up with is that there is absolutely no power coming from that one injector pin from the PCM.. has anyone ever heard of this before? It seems to have happened to the old pcm and the new one.. what would cause this?

 

Also, I have the three connectors going to the pcm. The newer diagrams are more accurate for my setup. Thanks for all the advice so far!

 

Here's the fuel injector diagram and pinout for PCM C2 for a '97 XJ, which may apply to your '96.





The 12 volt power supply to the fuel injectors does not come from the PCM, it comes from the ASD relay. Note in the diagram that there's a splice that devides the poer coming from the ASD to each injector. If all the injectors have power except one, the open in the circuit would be between the splice and the injector.

Injector ground signals (drivers) to activate the fuel injectors come from the PCM. The only way to see if the driver circuit to the injector is open or has high resistance would be by using an Ohmmeter, reading from the appropriate pin cavity at the PCM connector to pin 2 of the applicable injector connector.

It's rare, especially with two different PCM's but an injector with very low resistance can cook a PCM driver for that injector.

You can do some visual examination of the wiring harness at the rear outlet of the injector wiring manifold. The wiring comes out and does a turn into a larger wiring harness. It's at this turn that problems have been found where the valve cover has chafed through the wiring loom and into a fuel injector wire. Check this area out very carefully, cutting tie wraps and moving the looms around if required to get a good look at every thing.

 

So here's what I did to check and see if the wiring or the pcm is bad..

I cut the injector plug from the harness and soldered in new wiring and heat shrinked the solder points. The ground seems to have very little resistance and the power from the pcm is still dead.. with new wiring.

Has anyone ever had injector 4 circuit or any other injector circuits go bad? Because this is the second one that has encountered the same issue.. just trying to figure out if this is common or not..

 

Wiring problem is upstream then. The injectors all get power from a common splice that sits on the intake manifold. If you unwrap the harness you'll find it.

The PCM does NOT power the injectors directly. It cuts the ground. Infinite resistance is normal. If you see low resistance from the injector ground wire to the battery negative terminal with the PCM turned off you probably have a short on that wire as well.

 

The OP apparently didn't read a word I wrote in post #9.

 

Apparently!! OP was told 5 different times, in 5 different post, that the power does NOT come from the PCM......RR

 

I have the same problem with injector #4. I cannot afford a new pcm at the moment, but need to get my daily driver back up and running. Can I splice into injector connector? If so which one do you think will work?


Thanks,


Garrett

 

I am having the same issue. Replaced my ECU and it still doing the same thing when I splice into another injector wire the cylinder fires up and runs just the one wire is not getting any kind of pulse ground from the computer I've checked all the wiring it's all good the plug is good do not know where to go from here