1997 XJ, SE 4.0 Auto, left hand drive

My 13 y/o son bought the truck last year as a project to fix up before he turns 16, I drove it 60 miles home from GA just fine. It's currently in a state of disassembly for some rust repairs and re-paint (fenders, headlight panel, & hood off, door panels, handles & mirrors removed, headliner, etc.). Been driven in and out of the garage like this several times for sanding & priming. One day we randomly get a crank no start, gauge showed 1/4 tank of gas but added another 5 gallons anyway to rule that out

• Checked codes and initially got a P0351 primary coil circuit open. Checked for spark and there is none.
• Old coil resistance checked fine but there was a crack in the housing. Replaced primary coil, Cam sensor in distributor, cap/rotors & plugs as the truck needed a tuneup anyway. Cleared codes with scanner.
• Have 12V at the coil with key on, but I don't know of any way to check the driver wire with the tools I have available to me.
• Noticed Cam sensor insulation on engine harness was rotted and three wires going into the sensor were bare right before the plug. Cut back wiring and replaced with new harness side plug
• No other wiring around the cam sensor looked bad including the oil sending unit
• Removed and wire brushed all engine grounds in the engine bay (behind battery, down on the coil mounts, by dipstick tube, on firewall, 2 wires behind PCM)
• Checked 5V reference at cam & crank sensors TPS, etc., have solid 5V on the orange wire everywhere I checked. No shorts in wiring that I can find.
• Replaced crank sensor with new one
• Key on & slowly turning crankshaft by hand you can hear injectors click like you'd expect, ASD relay turns on & off though which seems odd.
• Swapped relays around in PDC
• Fuel pump runs every time key is turned on, don't have a fuel pressure gauge to check exact pressure but pushing the Shrader on the rail gives a good squirt.
• All fuses underhood & in cab are good, verified every fuse with continuity check.
• Checked Oxygen sensor wiring for shorts
• 12V to oxygen sensor good, 4.7 resistance on the upstream Oxygen sensor checks out good. Haven't checked the downstream sensor
• Check engine comes on with key on, then turns off a few seconds later like normal
• Tried two different OBDII scanners, tough time getting them to connect, cannot read any live data when cranking (was looking for RPM or something to verify crank sensor working). Sometimes it will connect to live data with key on, other times says it's not supported. No codes present with the scanners.
• Dash codes read 12, 45, 55. Conflicting info out there on what code 45 is.
• Battery voltage is good, been keeping it on a trickle charger
• Checked over the engine harness as best as I can without completely pulling all loom & tape off.
• Tried unplugging the TCM down by the gas pedal
• NSS seems to be working will crank in Park & Neutral but nowhere else.

Is there anything back by the driver taillight that could cause any issues? Previous owner towed behind an RV and had brake & turn signal wiring spliced in shoddily. I poked around back there and don't really see anything outside the lamps that's been messed with. Like I said fuel pump runs with key on and that's the only thing I can think of that would be back there and the only place the wiring has been touched. Jeep still has the stock, stereo, speaker and all.

ASD relay freaks out with key on, I understand the PCM controls the ground to the relay. That along with this all starting with P0351 I guess I am going to throw a new PCM at this unless anyone has other ideas for us to check first.

This is my sons project and he's using his chore & neighborhood job money. I hate just replacing parts and hoping for the best but I've tried to rule out everything else I can. New PCM online looks to be about $280, which is a lot for him. None in the junkyards around us. This has the project on hold as he was getting ready to buy paint next, but if we can't get this running he doesn't want to sink more money into it. Thanks in advance!

 

I just read you checked the reference voltage already my bad lol. Did this have its airbag recall done yet?

 

I would be looking again at ground wires in the engine bay and the engine. The ASD relay buzzing is a good indicator of a bad ground. Be sure to check the PCM connectors for corrosion.

Reinstall the factory sensors so you don't induce other problems.

 

I did check the 5V reference on the TPS but I was unaware of the airbag issues. NHTSA website says there are no outstanding recalls for our VIN. I will have to pull the seat and check, floorboards from under the truck look solid, no rust holes.

I checked crank, cam, TPS sensor harness for continuity to ground. Brown/yellow sensor ground wire had low resistance directly to the battery negative. None of the 5V orange wires showed any resistance to ground so I didn't see any direct shorts.

I did pull the plugs from the PCM and hit them with contact cleaner and checked to make sure all the plugs were fully seated. I am pretty confident in all our grounds too, I pulled the connectors and wire brushed them along with the screws that go into the sheet metal. I can touch my meter leads to battery negative and any of those ground screws and get strong readings. I think the ASD ground comes from the PCM which along with the P0351, and random connectivity issues makes me think the PCM is bad.

I ordered a power probe ECT3000 last night and will probe around to see if I can find anything else. Thank you all and please keep the ideas coming!

 

Yes the ASD ground does come from the PCM. You should be able to see the SRS module without removing the seat, if you cant see it, its probably under the center console near the shifter. That was the fix. They just rusted with the floor pans. Not a module you want rusting lol. SRS module dimensions 4.25 x 3.5 x 1.5. I really need to dust off my hot air station and get back into SMD board repair.

You've done a great job narrowing it down. I'd say its one of a few things. Hopefully its a simpler solution.
1) Primary coil was bad (causes intermittent problem) you replace it with the dist cap and plugs, maybe the wires were placed incorrectly? I know it sounds dumb but I've done dumber. Get a spark tester for 5$ @ hazard fart.
2) When you *Noticed Cam sensor insulation on engine harness was rotted and three wires going into the sensor were bare right before the plug. Cut back wiring and replaced with new harness side plug*
A ) Did you cut one wire at a time or numerous? Is it possible your cutting implement touched another already cut wire while proceeding to cut the next? Was the battery disconnected when this was performed? If so that shorted the ECM, could be a blown diode, resistor, or linear rectifier ground pin that gates the ground which is the SMD that takes 12v and makes 5V hot supply for the reference signal. Those can be easily replaced. Cost about 2$
B ) Those rotted wires maybe have already caused that problem

3 ) When you *Replaced crank sensor with new one* Did you use a used Chrysler part from JY/Ebay? A Million$ Mopar? Or a 15$ Overseas? Because the Chinese often use "non automotive materials" in sensors and computers. Magnets are ceramic and if the magnet is a regular neodymium ceramic magnet, 1 drop & its trash. Also excessive heat cracks them. Special magnets are needed which is why Mopar and used OEM last unless the motor overheated many times.

If you're not near a JY I can let you know when a 97 XJ comes in. Theres only a 2001 atm and its PCM is gone. Hate for the kid to have to cut grass all summer for a new PCM!

EDIT : If you cant get a 97 PCM 96 works in it too.

 

Early in the post you checked for spark and had none...after coil replacement , any spark yet? Pull off dist cap and have someone crank the engine..make sure rotor spins evenly. Did you have dist shaft out..? Have you done a compression test? Did you spray starting fluid into throttle body. The asd relay should not cycle or buzz.

 

I think I have an ecm for your year. Pic of yours w/ numbers showing I can check. Ric

 

Thank you all for the ideas. I looked under seat and Airbag module must have already been moved as there is nothing there. We have no Spark at all even straight from the coil, no I didn't pull the distributor out, didn't do a compression check as the truck ran fine and then just randomly wouldn't start one day. Also didn't use starting fluid as I already confirmed no spark.

I ordered a Power Probe with ECT3000 circuit tracer and got back on this today. Started probing around in the PDC, have good power going to the ASD relay, then found the 12V outputs of the ASD relay that go back to the PCM input and Oxygen sensor heater were about 1v low as compared to battery voltage. ECT3000 is showing a short on those two circuits, traced the wiring down to the gray & black connectors by the dipstick and we have a ton of wires with insulation peeled back from oil exposure. We need to get a new harness before we do anything else as I feel like I'm chasing my *** with this one. Even if we clean this one up with liquid electrical tape all the connectors are still in rough shape. If anyone has a lead on a solid harness let me know. This is an 4.0 SE auto, bare bones, no cruise or any options other than A/C & 4x4.

 

I would check the underside of that relay sometimes the pin backs off underneath and doesn't make full contact. and check all the grounds on the pas side of the block unless that's what you meant by brushed all engine grounds. They normally get all gunked up form a leaky valve cover

it is not impossible that the new cps is bad, I would always recommend a Mopar one but the CARQUEST premium works very well too I've used them on 3 different jeeps I had no problem. since you don't have a fuel pressure gauge shoot some starter fluid in the throttle body see what happens.

 

https://car-part.com/

THIS IS THE LINK TO ALL THE JUNKYARDS IN THE COUNTRY. IF YOU CANT FIND A PART ON EBAY I WOULD TRY THIS SITE

 

I can get you that plug tomorrow at the JY in Detroit. I'll ride the ebike down to save on the pushwater. I'll chop as long of a pigtail as I can. I'll put it on ebay for like 10 bucks just to cover the entrance fee at the yard. Ill pluck some other things so I make something. Would that help? I would just bypass the grounds before buying anything and see if it starts. Use some jumper leads. You can get alligator clamps for 3$ at H.F. Then use some wire to make double ended jumper cables. I can get that connector for free if its small (Not theft they like me), 5$ if I take 3ft +. Let me know man. You're doing great, just hang in there!

EDIT : If it is the CPS. I can get you one from the JY. I usually sell the chrysler originals for 80$ on eBay, but TEST your CPS first. Put your meter in Horseshoe mode and test the resistance on the middle and right pin with the notch facing up. If its OL or open loop or OC for open circuit its good. If there is any small resistance its bad. I measured one that had 1 ohm. It was bad. TBH If it was my kid I'd put in a new MOPAR sensor as when these go bad they leave you stranded. The hundred+ bux is just peace of mind.

 

I really appreciate the offer but hang tight at least for now. We have some liquid electrical tape coming and I've got the wiring at the black & grey connectors isolated to where we should be able to insulate everything and test fire. The insulation is eaten up on both sides of the harness (PCM side & engine side) from being soaked in oil under the loom and there were multiple wires touching including. We kinda decided if this works we are going to pull the engine to re-gasket everything fixing the oil leaks and do a better job repairing the harness or ramp up the search for a complete replacement.

Crank sensor does read open. I am pretty confident this wiring is the issue with all the random intermittent crap I've been chasing. I just hope the PCM isn't fried from it. I should have a better idea by this coming weekend.

I can't tell you thanks enough for your willingness to help though, it means a lot!.

 

Not a problem, Glad your CPS is working normally. Thats a pain to do. You're probably correct about the wiring. I guess I read your post wrong. Insulation makes sense. If one of the wires in those gray and black connectors is Brown with a yellow stripe. Thats the sensor ground to the PCM. I know one of those plugs is for the transmission and the NSS goes through it, I'd imagine the VSS too. So the Br/Yl wire should be there. If so lack of insulation is creating EMF near that wire. Increasing resistance and causing all sensor measurements to make zero sense to the PCM. Not allowing it to start as if the CPS was bad. Thats why we all think that. So if that ASD is still clicking there is a chance a gate wont close on the circuit board not allowing it to ground without some type of sensor reading. If thats the case it should be okay. If it shorted and arced maybe not. But an arc would blow a solder fuse on the board. Which would not allow the linear rectifier changing 12v > 5v for the reference signal to work either. I'd GUESS that its fine. But that other poster did say they have a PCM for you so its not all bad.

 

Well fellas, we got it. We pulled back the loom and separated all the wiring that the insulation had degraded, covered it with liquid electrical tape and it still didn't fire (still no spark). I went ahead and bought a reman computer and she cranked right up. I believe it was a combination of both issues with the wiring causing the ASD issues and odd communication issues as well as the coil driver in the PCM being bad. We have a couple of odd issues now that were not present before. The electric fan immediately goes on high with key on with engine cold, and it's idling just over 1000rpms. I'll take that for now over what we've been dealing with.

We still need to come up with a more permanent repair for the harness. I either need an all new engine & under hood main harness or just cut back as much wiring as possible and splice it like Dru mentioned. The black plug is broken and the insulation on both sides is damaged right at the plug. The gray connectors are damaged on the PCM side. Thanks everyone for the help!

IMG_3157 by EricT4R, on Flickr
IMG_3188 by EricT4R, on Flickr

 

I'd straight up trade the plugs you need for that broken computer if you're not already getting a core from the person you bought from & go that route. My electric fan was unplugged when I bought it and I'm guessing thats why. Those can be either a bad fan relay or bad coolant temp sensor. Not a biggie. At least your fan works! mine may be toasted lol.