Novak Conversions Jeep Wrangler YJ radiator

Fuel Injector quit firing again - full troubleshoot and ECM repaired

Drew S.

Drew S.

New Member
Joined
Sep 22, 2025
Messages
5
Location
Greensboro, NC
Fuel Injector quit firing again - I am a newly registered enthusiast. I have a '95 Jeep Wrangler YJ, 6 cylinders, 4L - Last month went through the whole exercise troubleshooting a misfire, Jeep running rough and I could small gas out the exhaust. Check Engine light was on. I verified code(s). Determined it was the fourth cylinder back and that it was "in the wiring" because the injector fired fine with adjacent injector connectors. Bought Noid Light Test Kit that confirmed. Installed a replacement connector/wire harness/pigtail on the affected fuel injector wiring. Still not lighting up the Noid Light. Finally sent the ECM to a company specializing in rebuilding that I found online. Reasonable cost to fix and returned promptly. Reinstalled the ECM and test drove for about 20 glorious minutes and was happy that all was good. A week or so went by before driving again. Last night took an evening pleasure ride for over an hour and everything was great, no misfire. Today jumped in for a quick errand and immediately saw the Check Engine light was on and could small the gas (from the exhaust). Ran the 10-minute errand dealing with the misfire again! When I got home, I confirmed with my Noid Light Tester that the fourth cylinder back was not firing again! HELP! What should I do next?
 
Thanks for the reply. I took Bosch Platinum's out and replaced with Champion 7034. Ensured 0.035" gap on all.

The codes presently displaying are:
1) "12" - The battery or computer was recently disconnected, which is True,
2) "27" - Issue with an injector output driver, which means the injector's control signal isn't being received or acted upon correctly. The problem could be a faulty injector, damaged wiring, or a problem with the powertrain control module (PCM/ECM) See previous posts.
3) "55" - Completion of the fault code display.

Plug tester shows all firing. I just pulled the 4th cylinder plug out and verified spark again by touching off t ground (a shocking experience :p). So, I don't think it is a plug wire issue. My injector connector for that cylinder is not lighting the Noid Light tester again.
 
Measure the resistance of the injectors. See if the problem cyl is different from the others.

You can also swap the injector with another one to see if the problem follows. Your injector o rings are probably old and hard, so if you try this I would get some new o rings.
 
the champsion 7034 does have the same heat range as rc12lyc, but the 7034 is for the modern wrangler, and rc12lyc is for older wrangler. keep us post as i would like to know if those plug work as good as rc12lyl. thanks
 
JKP - I checked the resistance on all 6 cylinders. They were all 14.7 ohms except the troublesome #4 cylinder was 14.6 ohms, only a difference of 0.1 ohm. I read that this should not be a concern because the spec for '87 - '95 YJs is 14.5 ohms +/- 1.2 ohms. Does that sound right to you?
 
Dieselearl - Thanks for the info on the spark plugs. I remembered putting the previous Bosch Platinums in the Jeep but cannot remember how long ago (it was at least 6 years ago). I was quite surprised at how bad the Bosch Platinums had looked. I have used this Jeep as my weekend fun cruiser for about 8 years putting very few miles on it. Before that my son had it as an everyday driver for about 10 years. I'll keep the Champion 412s in mind if I get to the point where I need to change them out.
 
Novak Conversions Jeep Wrangler YJ radiator
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