CEL and Missfire

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.

Start by pulling the plug wires one at a time while the engine is running. When the miss stays the same you'll know which cylinder is misfiring and you can trouble shoot from there. If it doesn't change it could be an injector issue.

You nailed it on the injector issue. Checked all the plugs/wires with a spark tester, everything was strong and uniform.

Was throwing a CEL 27 which is for the injector circuit, started pulling injector plugs, they were so corroded I couldn't even get a reading with my multimeter to check the resistance. Cleaned all the injector plugs, reassembled and found that injector #3 was the culprit.

From what I can tell the pervious owner gapped the plugs extremely wide to offset the crappy flow from the injectors. Seemed to run fine before, but runs even better now.

For those wondering the resistance on the injectors should be around 14.8-15 ohms.

Glad you found it. I replaced my injectors awhile back and had to clean all my plugs as you describe. It amazed me that it even ran with all the crud in the plugs. It runs much smoother with the new injectors but I'm at a loss if it is the injectors or the clean connections.

As far as CEL codes go I'm useless as my Renix doesn't have a CEL or throw codes. We trouble shoot with a multi-meter.

how did you go about cleaning the injector plugs? was it the male end of the connection or the female?

small emery board and contact cleaner.

I know this sounds dumb. But this summer I bought a dead jeep. It had sat for who knows how long in a garage but it was covered in dust. Amazingly the battery still had charge. After I put the new engine in it wasnt firing ln cyl 1 and 2. Even with the battery hooked up with jumper cables it wasnt firing on those 2 and I had no check engine light. When I replaced the battery the BRAND NEW engine ran perfectly. If all else fails its not a bad idea