Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - Craftsmancollab.com
Test #1

Rented a noid light set from oreilly's. As suspected by the P0201 (electrical circuit open/problematic on injector #1), all flashed under running conditions except #1.

The #1 connector was charged up around the base of the plug and also the plug itself was in poor condition. I chopped it and wired in a replacement plug. While the wiring was bare above the plug I tested the noid lamp there. Nothing. Plug shouldn't be the issue.

 

Test #2 Positive Voltage

Next was to determine if the plug was getting positive voltage. There is an orange/green wire that provides all injectors with its positive charge. This runs from the ASD (auto shutdown) relay and provides power while running or right upon turning the key on. Using a good ground in place of the injector plug ground, each connector tested 14v running. This is the leftmost plug on the fuel injector looking down at it from the drivers side. Or/Gr wire.

great. the asd appears to function properly and all injectors get voltage from the positive splice, therefore I would think no short up from the injector to the battery.
Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - Craftsmancollab.com

 

there aer other codes I guess?

Simple code p0201 - the injectr gets 12v from ASD on common wire for all injectors and the other wire (driver) goes to the PCM. The PCM does not see 12v on white wire.

With KOEO is there 12v on both the orange and white wire at inj?
yes =somewhere between inj and PCM the wire is compromised.

Did you ck harness at rear #6 cylinder a known rub thru area,
no might be bad inj or connector.

 

there aer other codes I guess?

Simple code p0201 - the injectr gets 12v from ASD on common wire for all injectors and the other wire (driver) goes to the PCM. The PCM does not see 12v on white wire.

With KOEO is there 12v on both the orange and white wire at inj?

yes =somewhere between inj and PCM the wire is compromised.

Did you ck harness at rear #6 cylinder a known rub thru area,

no might be bad inj or connector.

Thanks for the diagram to add to this and input. Only code is p0201. Will clear all codes, immediately upon startup it flashes right back. Noid light proves open circuit.

I inspected it and did not see any run through. All of the engine bay harnesses I had stripped of the rotten plastic/tape a month back and inspected before rewraping with some extra protection. Only exposed wire was at the base of the #1 injector connector. Hoping that couldn't have shorted the two together without the resistance of the 12ohm injector and shorted the computer.

 

Test #3 Continuity from injector connector to PCM terminal B.

At this point there is a definite grounding issue. The pcm pulses the injector by intermittently grounding the circuit through its computer.

#2-6 are proper and therefore able to be grounded and ungrounded in the appropriate manner.

#1 gets no light illumination, therefore indication of a stuck open circuit. Whether due to a split wire, missing pcm or other issue along the way to the ground it is not being completed and therefore spraying no gas.

So here goes checking resistance between the PCM connector B (white middle) to the appropriate injector ground terminal.

Here is a chart I found on the PCM wiring codes showing the control of each. The terminal numbers were off on mine so I went by wire color. Wrote in corrected terminal positions for a 2000 4.0 A/T computer.

Using this the resistance (ohms) of each ground circuit is tested between the injector connector and the pcm connector. This wiring ties into the thick bundle along the firewall and then splits into the valve cover positioned wiring.

#1-#6 all made continuity from the connector back to the pcm terminal. Resistance grounded out to 0.00 ohms. #1 did jump around a bit higher before hitting the 0.00, #4 sat between 0.00 and 0.80, #6 jumped between 0.00 and 0.50. Overall very low resistance and power passing through from the meter.

This would lead me to believe the wiring is intact from the pcm to the injector, correct?

Only oddity here is that last night the #k5 (listed as ground control over #3 injector) terminal on the pcm made continuity to the positive terminal on the #1 and #2 injector terminals. Today it did not repeat that.

Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - craftsmancollab.com

 

Another note:

All injectors are new with 0 miles as of yet. Have been run with the new engine in a break in cycle in the driveway.

All have a resistance just upwards of 12ohms. Swapped #1 and #2 injectors and the issue remained on #1 so ruling that out. New fuel pump and cleaned lines as well, fuel pressure is at spec. This would tend to show up as an issue on all anyway unless a bad injector.

 

Managed to backplug into the pcm terminal with a sewing needle. As was mentioned, this would tend to show the continuity of the circuit up until the pcm.

First image is of injector #1 terminal, grounded to the body. ~14v
Second is of injector #3 for comparison.

So, what are the other options from here? My pcm is fried? Maybe I'm still thinking cause I don't want to accept dropping that $$$ and hassle after having just replaced most everything else in the engine bay... just empty every pocket.

Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - The Grove

 

PCM wiring and dead injector driver - Jeep Cherokee Forum

Just gave this a read. Didn't think about jumping the ground circuit off of the #6 injector circuit as a quick fix since they would be timed together.

Edit from comment below: THE ABOVE IS INCORRECT
"the injector pulses from 1 and 6 are not timed together they are 180 out on cam and 360 out on crank as far apart as any 2 injector pulses ever are

What is timed the same for 1 and 6 are the coil grounding pulses to the rail but NOT the injector pulses they are truly sequential

additionally tying two injectors together in parallel would half the resistance/impedance would draw about twice the current and might damage that injector driver"

Also cracked open a spare pcm from a manual '98 I had around from another project. Got a visual on what looks like the 6 circuit board drivers that would pulse the ground.

Will have to look into testing them to pinpoint the failing one and see if I can find details to get a replacement in. My old man is a long time electrician and computer systems engineer so repairing the pcm with him may be an option. Otherwise Cardone sells a flashed and programmed for $400 through oreilly's. Junkyard could be an option if a 2000 shows up. Most other online places have F consumer affairs reviews, and dealers run a rebuilt computer with a reflash to program vin/mileage IIRC.

 

https://www.cherokeeforum.com/f2/how-replace-blown-injector-driver-pcm-95-a-248325/

Look into rebuilding the pcm with a new driver on an earlier XJ

 

Look inside a '98 pcm I had sitting around. The driver pictured at the ground tip ohms out to #1.
Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - The Grove

Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - The Grove

 

I did follow this - seams a post of mine got lost - BUT you dont need help you can do.

As far as opening PCM's my experience is it never ends well.

There is a colleague here 'waterluvr' who I consider a PCM authority WJ's mostly but he is the go to PCM guy - might want to ask him about replacements.

 

I did follow this - seams a post of mine got lost - BUT you dont need help you can do.

As far as opening PCM's my experience is it never ends well.

There is a colleague here 'waterluvr' who I consider a PCM authority WJ's mostly but he is the go to PCM guy - might want to ask him about replacements.

I'll keep that in mind and reach out to him, thanks.

I wouldn't have been so sure to mess with the internals on my own, but my dad is a computer engineer that has been working on circuit boards for years... I'll source a replacement driver and have him do the installation.

 

Check the fuel injector wiring harness at the point it bends around and makes contact with the threaded stud at the rear of the valve cover. That stud is notorious for rubbing through the injector wiring and causing a short or two to ground.

 

Inside of the now repaired 2000 computer. Single sided board, much easier to disassemble and pull then the '98 I had trialed on.

Part # for the OE was 43U02 Motorola. Could not find that part anywhere, used an equivalent driver. Can post the part # if anyone is ever looking.

My dad has been in satellite and computer communication/engineering for decades and did the install of the new chip. Would not recommend to an inexperienced electrician, but with caution is definitely doable. Not the blue wire as an extra link as the board is 20 years old and may have lifted with the desolder of the OE.

Testing tomorrow, then if all is well will caulk some sealant to re waterproof the assembly
Update: Full P0201 Fuel Injector Circuit Diagnosis/Repair Post - craftsmancollab.com

 

Hope it works-

Nice stick with it attitude, I'm not a dig into the PCM guy, but enjoyed the updates, pictures and learning. :2thumbsup:

 

Fired it up and CEl is not illuminated. Runs with no misfire.

Saved a good couple hundred bucks. Not bad.

 

Fired it up and CEl is not illuminated. Runs with no misfire.

Saved a good couple hundred bucks. Not bad.

Nice job, good thing your dad was experienced in that very precision type of job. I've replaced a lot of components and IC's on circuit boards and it's not an easy job for even an experienced tech.

 

Hello,97 cherokee country I6 4.0 ...i been behind the scenes of this forum for months scanning google and such , should of made a account the first day , but i was clueless and didnt know much and slowly learning . I basically had alot of problems(codes) at first now im down to 2 (p0201) and the map sensor one but this one is the most frustrating one because i re-did the whole harness for all the injectors all the way down to the o2 sensor with everything attached to this harness and the c107, didnt go further past the other side of the ,c107 (i think it was the c107 next to the oil dip stick and the canister if thats normally where it is) I actually took of that harness and re did it 3 times(cut out and replaced/soldering sections of bent or curved;stuck wires because still had something wrong but it did clear alot of other things . Now that i have been looking thru and reading everything and checked every single wire even down to the bottom of the fuse block next to the cruise control vacuum holder or whatever its called , im nearly 100% positive its the same problem you had. It is 2021 and the corona virus pandemic is still here and ruined my life not with the disease itself but money wise since im an hvac tech and got laid off and been laid off just doing side jobs here and then . So biying isnt a option . .. what was the oart number to those drivers snd anything else to add to my knowledge is very much appreciateed . If i cannot see myself to fix the pfm like you i wont undo the drivers so i been just trying to rewd the circut board with a multimeter to tru and difure out where the } for the white connector goes and figured out it ended up where tou ste exactly . . If intell nyself i cant resolder it i will just solice into ninber 6# as it is my last hope before i am sleeping in the snow since im about to be left without a house

 

Anyone know the part number for a 1997 cherokee country 4.0 fuel injector pcm transistor ? Sorry idk if i made this right or where to even start on this web

 

MJE355T is the part number equivalent to the Motorola U4302. For anyone that still has not found that P/N.

 

This from post #9 is inaccurate
"Just gave this a read. Didn't think about jumping the ground circuit off of the #6 injector circuit as a quick fix since they would be timed together."

the injector pulses from 1 and 6 are not timed together they are 180 out on cam and 360 out on crank as far apart as any 2 injector pulses ever are

What is timed the same for 1 and 6 are the coil grounding pulses to the rail but NOT the injector pulses they are truly sequential

additionally tying two injectors together in parallel would half the resistance/impedance would draw about twice the current and might damage that injector driver

 

used pcm should be plug and play if same year engine tanny and calif vs federal emissions but given history I'll bet a wire/connector issue from pcm pin to injector or from asd relay to injector