X2 had the same thing happen to me in the same bump in the road but it was a 2 trip cel that was going off.

 

my neighbor has a 98 jeep cherokee 4x4 xj as well. all same as mine except his is a limited. will it be ok for me to swap his pcm just to check if mines bad? wont mess his up will it? just wanna see if thats whats wrong with mine but dont wanna mess his up.

 

by the way y'all, i did unplug injector 5 and im assuming that would be counting number 1 injector nearest to the front of jeep and 6 being closest to firewall right?? because when i unplug number 5, i notice a difference in the engine running unplugged and when plugged back in, its a slight better. i also unplugged the computer pcm plugs (3) and cleaned them with electronics cleaner spray and plugged back in. no difference there. ive inspected grounds and seem good there. ive checked the o2 sensor plugs and wiring to see if anything was damaged and saw nothing there. this sucks!! i hit a small dip in the road and this happened!!

 

also so i have a dmm now. so i have checked the ohms on the injector while unplugged. they are all within tolerance. 12-12.5 ohms. how do i check everything else? like the plug from the computer to the injectors and what should they read and colors i should read. also how do i test the injector plug itself? voltage? and with it running or not? thanks very much y'all!! im having such a hard time with this.

 

i just did some more checking. its running super rich. pulled out 3 spark plugs. 3 from the firewall forward and all of them are jet black soot. the other three are fine looking as if they are burning fuel properly. seems as if the others arent firing possibly. checked the cap and rotor and plugs wires. all look good. i also did swap the pcm for my neighbors jeep that is also a 98 xj with 4.0 4x4. it ran smooth for about a minute then it started slightly missing and getting worse. hmmmm. weird. any help or info?

 

You have 2 upstream O2 sensors correct? Sounds like bank 2 O2 sensor could be trashed.

 

The PCM supplies +12V to each injector coil full time and switches the other end of the injector coil to ground when it wants it to open.
It looks for an inductive kickback from the injector coil to verify that it responded. If it doesn't see that kickback, it sets the P0205 code.
If there is a short in the control side of the wiring harness, the injector will dump gas and you'll get the "injector driver" fault code.

At this point you may want to disconnect the connectors at the PCM, make sure they are clean and in good condition, then take a couple of resistance readings.

With the PCM connectors and the #5 injector plug disconnected:
Measure resistance across both pins in the #5 injector plug. Should be infinite resistance.
Measure resistance from each pin to ground. Should also be infinite resistance.
Repeat all measurements while shaking and twisting the injector harness at the injector and then the PCM end.

Measure from PCM connector B6 to each pin in the injector plug. (see drawing below. I figured out how to take a screen shot of my manual, lol Yay me. It's a '97 manual, but I believe it's the same here)
One should show infinite resistance, the other should show zero ohms (indicating a good connection)
Now plug the injector back in and check resistance at the PCM plug B6 to ground. Should be infinite. Repeat while shaking and twisting the harness at both ends.

 

Some very good research and advice above by Radi.........definitely worth following.

 

hey turbo, which o2 sensor is bank 2? i have an o2 near the cat and one closest to the exhaust manifold header. looks like it may be on the y pipe. thanks ill try that. Radi, thanks very much, i will try that as well. im at the point of trying anything. thanks again everyone for your help. so greatly appreciated!!!

 

X2 ^ Great info, thanks Radi...and nice photo as well!

10ac...I think what Turbo is suggesting is some later 4.0's have two "upstream" 02 sensors, and one being bad could explain (it's) three cyl's carboning up. If you only have one on the manifold, and one post -cat, that might not be the case. I might be completely off base here though.

From the research I did before, (from that google search post #15), Radi's approach seems pretty hot.

 

Radi, so i did the test. heres what i read:
With the PCM connectors and the #5 injector plug disconnected:
Measure resistance across both pins in the #5 injector plug. Should be infinite resistance.(its fluctuating 4 to 6 ohms about)
Measure resistance from each pin to ground. Should also be infinite resistance.(pink w blk stripe is inf. and green w orange stripe is 2.8 ohms)
Repeat all measurements while shaking and twisting the injector harness at the injector and then the PCM end.( no change)
Measure from PCM connector B6 to each pin in the injector plug. (see drawing below. I
One should show infinite resistance, the other should show zero ohms (indicating a good connection) (pin 15 at pcm plug to pink w blk stripe is infinite and green w orange stripe is 12 ohms)
Now plug the injector back in and check resistance at the PCM plug B6 to ground. Should be infinite.( is 15.6 ohms)
Repeat while shaking and twisting the harness at both ends.( no change)

 

also like i said before y'all, when i tried my neighbors pcm, it ran perfect for about 1 min but started to seem as it were starting to act up again so i shut engine back off because i didnt wanna risk messing his pcm up. his jeep is same as mine except a limited.

 

I don't want to distract from you and Radi chasing this down. But...2.8 ohms isn't much resistance. That might be your problem!

You got that with your PCM disconnected? Me, I might even rig a test light and actually see that draw current , that green w orange to ground. But hey, "DFlintstone!" ??

 

yes, with pcm disconnected. if that is the problem, and seems it is. from what i read on testing, should be infinite as well as other tests i performed as stated above. what is causing that and what to do to fix it? and thanks again to all of y'all for helping. i just want my jeep purring again....

 

It would seem, following Radi's understanding, that that green w orange is touching ground somewhere. At least some. Being somewhat of a bonehead, I might do the same test on some of the others and see if they are different.

If INDEED that is the issue, a coupe things. If a wire in a "loomb" somehow gets too hot, it can cut right through the insulation to the others, like a hot knife.

Also there is a split in that casing. That split can end up on the bottom where the gang goes around some corner, where vibration and time can wear through the insulation to let it make contact to ground.

If I isolated that one, being grounded, I suppose I'd get agressive about finding where it's grounding. Starting with a visual over anything that seems in the neighborhood, then pulling the casing to look for any sign of something melted, out of line.

That said, you might want to wait to see what Radi, (or anyone else has to say) ...