I have a 94 cherokee with the 4.0, I ordered the accel tune up kit with cap, rotor, plugs and wires.

I noticed the accel plugs that came with the kit were the wrong plugs so I went and picked up some champion copper core 412's gapped to .035.

Well after installing the new cap/rotor and wires I was getting a missfire and check engine light, it starts and runs, just a little rough, sounds like a single cylinder missfire possibly. I checked and re-checked the firing order. 1-5-3-6-2-4, pulled all the wires, re-installed to ensure a good connection. Still missfire and CEL. I even made sure the engine was at TDC and looked what direction the rotor was pointing to start my firing order.

So far heres all the combos I have tried without being able to get rid of the missfire/CEL.

-old cap/rotor with the new plug wires, new and old plugs

-Old cap/rotor, New set of wires from NAPA new and old plugs

-Old cap and rotor, NAPA wires and OLD plugs

-New Cap/rotor, NAPA wires, OLD plugs.

-New cap/rotor, new plugs, napa wires.



Im at a loss as to what to check at this point. Could I have knocked something loose? Could the coil have gone bad and is just a huge coincidence?? Or something completely obvious? Im not able to use the old plug wires because they came apart when taking them off.

Any help is appreciated.

 

One combination you failed to test .....

Old Cap / Old Rotor / Old Wires / Old Plugs

Every combination you tested has NEW WIRES ...... every combination you tested has PROBLEM.

My guess is one or more of the NEW WIRES is BAD.

It happens !!!!!


NEXT TIME: ALWAYS change one item at a time and TEST after the change. This way you will know what causes the problem.

PLUG WIRES --- Change them ONE AT A TIME .......

Remove One Old One ..... Install New Replacement
Remove One Old One ..... Install New Replacement
Remove One Old One ..... Install New Replacement
Remove One Old One ..... Install New Replacement
Remove One Old One ..... Install New Replacement
Remove One Old One ..... Install New Replacement


When you remove all six, then go to install all 6 new ones .... you run the risk of crossing them up.

 

Unfortunately I cant use the old wires, they literally came apart when I was removing them, old and rotted.

I've also tried 2 sets of new wires, the Accel and Napa brand, my original thought was I had a bad wire.

 

Get a spark tester and put it on each plug wire ( one at a time ) to test for spark on each wire.

They look like this .........

 

I will get one and report back. Thanks for your help.

 

You can test individual spark plug wires for resistance with a basic multimeter. You would want to pay close attention if one of those wires is much different than the others. BUT you mentioned that you did install two new sets of wires during your troubleshooting so the problem is likely not with a wire.

You absolutely need to rely on the check engine light trouble code to guide you to your root cause. What is the exact code? That code is going to help lead you to a fix. Having that exact code will help you with your "swap and follow" technique. The bottom line is this. If you did NOT have a misfire before you did the tuneup, the problem is somewhere within the tuneup hardware.

Here is how to extract code data from your 94 XJ. It's very easy.

Retrieving OBD codes on the Jeep Cherokee (XJ) OBD1 Models: 1991-1995

1) Start engine (if possible). Move transmission shift lever
through all positions, ending in Park. Turn A/C switch on and then off
(if equipped).
2) Turn engine off. Without starting engine again, turn
ignition on, off, on, off and on within 5 seconds. Record 2-digit
fault codes as displayed by flashing MIL.
3) For example, fault code 23 is displayed as flash, flash,
4-second pause, flash, flash, flash. After a slightly longer pause,
other codes stored are displayed in numerical order. When MIL begins
to flash fault codes, it cannot be stopped. Start over if count is
lost.

NOTE: A "5-5" will always occur to signal the end of the sequence. Some will flash the "1-2" code indicating a recent battery disconnect even if you haven't done it. Ignore these two codes, and mark down all others.

P.S. Triple check your wire configuration. I know, I know.......but I've seen guys chase their tails and eventually find an issue with that. And your coil can easily be tested for both primary and secondary resistances with a meter, so do that if you get stuck.

Good luck, get us that code and keep us posted!

 

I will check the code right now, I got a spark tester and I am getting spark with no irregular frequency/quality to all cylinders.

I really appreciate your post by the way, I'll post back after I can check the code.

 

Getting the following codes..

12 (normal)
27
27
5-5 (normal)

If I'm not mistaken 27 is for fuel injectors?

 

I'm pulling the electrical plugs on the injectors and every one of injectors is so dang corroded that i couldn't even get good enough contact to get a resistance reading with my multimeter.

Is it possible that now I have healthy spark the injectors just simply aren't getting good enough contact? The seemed to run well before I changed the cap/rotor.

The electrodes on the old plugs were extremely worn down and the gap was pretty massive.

Hmmm

 

Make sure that you didn't knock a injector plug off. While running, pull one injector plug at a time & listen for the engine rpm to change. No change would be a bad injector.

 

I'm going through and checking all those right now. Both resistance across the injector as well as the connection.

 

Whelp, I figured out the problem.

The plug on the #3 injector wasn't making good connection at all. Pulled all the injector plugs, cleaned, reassembled and now everything is running like it should.

My guess is the PO gapped the plugs really wide to offset the crappy flow from the injectors.

For those of you wondering, the resistance across the injectors was 14.8-14.9 ohms all the way across.

 

Glad you got it sorted out.

 

Thanks for the help, I was beating my head against the wall focusing on the ignition components when all it did was cause another issue to surface.