Injector harness issue

Hey all. I picked up a pretty rough 96 XJ, 4.0, manual a little bit ago for a winter beater. It's got a bunch of issues, but ran and drove fine. I picked up a slight hesitation/miss at low load (cruising) conditions that has progressed to a bad misfire at any/all rpms and not matter if cold or warm. New plugs/wires when I bought it, and it ran fine for a few weeks after I did that, so that shouldn't be the issue.

I put a scanner on it and got a bunch of codes. They were misfires for all cylinders and low voltage on injector circuits. I'm assuming that would be the ground for the injectors? The diagrams I've looked at seem to show a common ground for them, so I'm hoping that's all it is.

My question is this, other than checking the injector harness for continuity/resistance, is there anything else that I should be thinking about that would cause all of the injectors to be acting up at the same time? I was thinking distributor, and maybe crank position sensor for the running rough, but with those codes it seems more likely wiring to me.

Thanks for any input on this one.

The injectors on the 96 have a common power supply coming from the ASD relay. The injectors actuate on the ground side in the PCM, just the opposite of the Renix. Maybe a PCM ground issue?

I think it is the dark green and orange wire. The injectors share the same power circuit as the coil and the alternator power in. It is possible something is partially shorting out and sucking the power down for the injectors or maybe the coil is misfiring? Coils are funny, they don't have to be good or bad, but can slowly degrade as an internal short does more damage over time. The first thing to always check is the high voltage cables, moisture can get into the boot ends and can cause periodic high voltage to ground issues. Maybe swap the ASD relay with another similar relay, Unlikely to be an issue, but just in case.

My 96 has been doing the same thing recently, just occasionally, I'm trying to decide what the issue is. Seems to make no difference hot or cold, but I have noticed it happens at around the same RPM and/or pedal position every time. Mine picks up a stutter above idle or maybe around 1000 RPM occasionally.

I'm wondering if it is the beginning stages of CPS failure or maybe a bad spot in my TPS. Or maybe just some water in the spark plug or coil wires causing intermittent issues. These intermittent problems can drive you nuts, most times you have to catch it in the act.

I have had issues with the ignition switch to ASD relay activator (power in to the relay coil) circuit before. My ASD relay would buzz and not close completely occasionally. Turned out to be a flaky connector. When this happened the motor wouldn't stutter or miss, it would crap out completely.

One thing that can cause voltage issues in this circuit is a coolant leak, often overlooked. Some of the voltage runs to the outside of a coolant covered alternator or from a connector to ground and sucks the available voltage/amperage down. Usually shows up with a simple voltage check someplace in the ASD to coil circuit.

Let me know what you find out, I'd like to get mine right before it completely craps out.

So I popped the hood and fiddled a bit tonight. It's the harness for sure. I can move the wires and the engine stumbles. Never found the root cause as it was running better after I kinda tucked the wires back in place. Too cold to monkey with it any more right now.

Thanx for the info, I'll try shaking the harness and see what happens.

drg0708 said:

So I popped the hood and fiddled a bit tonight. It's the harness for sure. I can move the wires and the engine stumbles. Never found the root cause as it was running better after I kinda tucked the wires back in place. Too cold to monkey with it any more right now.

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Look for harness penetration in this area:

On my stepson's 93 long ago I had a problem with a splice in the harness. The common positive supply comes from the distributor area, and from there, it is sent to the various injectors by splices. It's possible that a bad splice somewhere early in the harness could cause subsequent branches to go bad.

I went through many hoops trying to find the problem on that one, because it only went bad when it heated up. It started fine, and passed all injector tests, but as it heated up the resistance rose, and at about 9 volts the injector stopped working.

Thanks for the input guys. I think I have it sorted. One of the previous owners had been in the harness before, looks like they spliced some of the grounds from the throttle position sensor etc, but hadn't touched the injectors. I replaced the splice point (what a rat's nest) for the injector grounds which was right above the third injector, give or take, and re-tucked the rest of the harness. It's running much better now. Fingers crossed.

drg0708 said:

Thanks for the input guys. I think I have it sorted. One of the previous owners had been in the harness before, looks like they spliced some of the grounds from the throttle position sensor etc, but hadn't touched the injectors. I replaced the splice point (what a rat's nest) for the injector grounds which was right above the third injector, give or take, and re-tucked the rest of the harness. It's running much better now. Fingers crossed.

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Good to hear. Just to keep things straight, especially as these forums are archived, the common supply to the injectors that is spliced here is the positive 12 volt, not the ground. On Chrysler systems, the ground is switched by the computer. Earlier Renix systems switch the positive.

If you find a common source for the +12 volts before it gets to the harness, you can (with power off of course) use an ohmmeter to check resistance from there to each injector. If there's any resistance at all, it can indicate a poor splice, which may work well when it's cold, but get worse as it heats up.

Oops, yes, my bad. The splice I redid was the positive (dark green and orange on this 96) wires.