2000 XJ No Spark, good CKPS, bad TCM.

Hi all,
I have been pouring over every post I can find for the last week or two, trying to find some poss solution to my very weird issue, and no luck so far.

A little backstory-
I just finally finished a new stroker build after a broken piston about a year and a half ago. Everything worked and was fine when I pulled it. Got the motor in, everything hooked up, and was excited to finally get 'er going again. Turn the key and....

Nothing. No gauges, no turn over, no fuel pump prime, nothing. Eventually get a No Bus error on the cluster, occasional CEL, and airbag light. Also have strange issue of backup lights receiving about 5 volts all the time.

So, I start researching No Bus issues. Lots and lots of threads about bad connections at the cluster, the PDC, grounds, ASD circuit, etc. Run through all of the probable solutions. Eventually find a note buried somewhere about the TCM. Unplug the TCM, and voila, no bus is gone, gauges work, fuel pump primes, no CEL (initially), backup light issue is gone, and she will crank. Still no start. Seems obvious bad TCM, but nothing I can find indicates that it is necessary to run, nor should it cause my issue.

Of course I see 1000 posts about bad crank sensors being primary culprit. Run through every diagnostic I can find described, and it checks out.
What I have checked/done:

• Crank sensor checks good. No resistance through the leads, it is getting the 5 volt CCD bus signal. PCM seems to be reading it, no change in gauge behavior when disconnected. I can connect to the PCM through DTC and pull codes. I replace it anyway, still no spark.
• Disconnected, cleaned, and reseated every ground I can find.
• pulled every fuse and relay, tested, cleaned contacts and replaced
• All others sensors on the CCD bus have appropriate voltage
• Verified Injectors are firing
• Fuel pump does prime, and I have 12v at the coil during the inital key ON.
• pulled the coil, and tested for spark by inserting all the plugs and grounding them, no spark visible. Tried replacing the coil just in case, no change.
• Am getting proper bias voltage through the DTC to PCM (2.4-2.5 volts)
• Pulled, cleaned, and reinstalled NSS. No change, though do still have wierd backup light issue, and No Bus if TCM is reconnected.
• only codes listed are 1698 (no tcm communication, because it is disconnected), and P1800, which I find several different explanations of, but mostly related to TCM issues as well. I cannot connect to PCM if the TCM is plugged in.
• PCM is new, was replaced becuase of previous error indicating bad memory block. Behavior is the same when I swap the old ECM in.
• No apparent problems with wiring, though I haven't completely stripped the harness apart, obviously hoping not to.

So, here is where I am. I have narrowed it down to no spark. Acts as if the ASD circuit is engaging, and shutting down spark, but everything seems to check out, and it should work. That usually points to the ECM not receiving a timing signal from the CKPs to fire, but it seems like it is.

At this point, I'm about ready to take a gas can and match to it.
Is there another means of verifying that the PCM is actually receiving a signal from the CKPs? Not having the TCM connected should not affect any of this, correct?

The only other thing that I haven't mentioned is the RKE (keyless entry module) is currently disconnected. I did try to plug it back in earlier, with no change in behavior. That also should not affect this, correct?

Any thoughts would be appreciated.

I have seen very strange things when relays fail even if they click and have the proper resistance. Have you switched the relays to different positions in the PDC? What is your battery voltage at the cables....not the posts.

Find a pinout of the 2000 pcm. start testing continuity of the cam sensor, CKP, tps, iac back to the pcm. Check grounds again. Did you have a tcm issue before you did the rebuild?

Yes, switched the pdc relays, and swapped the ASD relay for a new one just in case.

Will have to double check the voltage at the starter end, good thought. Was 12.2 at the batt.

Yes, chasing all of the wiring between the sensors and the PCM is my next approach. Will advise.

Had no probs with the TCM or anything other than the memory error on the old pcm. Everything worked fine.

Thanks for the thoughts.

Well, the plot thickens.

Tested most of of the sensor circuits from the PCM connectors to the individual sensor connectors, as well as the ASD relay, all checked out good. Didn't get to the O2's yet.

Voltage from the batt to the starter and pdc are also good, not more than a couple tenths of a volt difference.

PCM grounds are good.

As far as I can tell, this thing should be working. But it doesn't.

What I'm not 100% sure on is if the TCM and RKE being disconnected will activate the ASD circuit to disable spark. From what I can find so far, that answer should be no.

I haven't been able yet to chase or check the wiring between the TCM and the trans, or wherever it goes, so unsure what the problem with that is.

Getting closer to getting the torch out...

you can start the jeep with the TCM disconnected. and im guessing it would start with out the RKE module. assuming it does not have any factory alarm.

my guess is you have a short on one of the sensor feeds if a voltage supply shorts to ground it will prevent the ecu from booting. are you able to pull live data from the ecu? or do you just have a code scanner?

the one test to check the crank sensor is the rpm needle will just nudge off of the peg to around 300 rpm when its cranking if it works. i found out its really easy to break when removing or installing an engine.

also i would check the wiring down to the transmission solenoids if there is a short there. reverse lights loop around in those connectors too. also very easy to bang up removing an engine.

It does have the factory "alarm". But, I have also tried it with the RKE connected, and it behaves the same, and I do not get additional CEL, or No Bus issues with it connected.

Don't recall if I have noticed the rpms moving during cranking or not, but I can check that. But, I have gone through the CKPs several times, ohm'd it (checks good) ohm'd the wiring from the PCM to the CKPS connector, checked it against ground, verified it is getting proper bus voltage, etc, and all have checked out good. Even replaced it anyway, and still behaved the same.

I will go back and check the other sensor leads against ground, to be sure that isn't a problem.

Nope, just a dumb bluetooth code scanner/interface. I will have to check around to see if I can find a better scanner I can borrow, that would help a lot (assuming the PCM is working correctly).

Yes, I do plan on checking the trans harness for issues, just didn't get to that last night. I agree that wiring damage is the most likely culprit there, as it was all working fine when I pulled the motor out, though I don't recall bashing anything putting it back in. Who knows.

im not sure if they still ground there but make sure all the grounds at the dip stick tube are connected. and that the ground strap is good. i think they still had them on later jeeps.

It is. As I mentioned in my initial post, I have gone through, cleaned and re seated every ground I can find. And, I did verify that the PCM is getting good ground last night.

Going to order a better scan tool/interface today, and see what that can tell me.

NEVER GO FULL RETARD.

That is going to be my new mantra- to myself.

Short story, she is ALIVE!

Long story, (aside from the fact that I am a fu^%#*ng moron) for those who care, or just want to avoid making the same REALLY stupid mistake that I did:

I have spent the better part of the last three weekends and several evenings trying to figure this thing out, and none of it was making sense. It should have worked.

I tested every sensor, chased and tested impedance on every circuit/wire between the sensors, ECM, PDC, cluster, etc. Many multiple times.

I removed, tested and cleaned every fuse, wire connector, relay, ground*, and contact I could find.

It def acted like the CKP was bad, but it wasn't. The ECM was getting input from the crank sensor, and the crank sensor tested good. I had fuel, and injector pulse, but no spark. It would prime the pump and then shut down, as it should with the ASD circuit.

I even pulled the crank sensor out again, confirmed it was working and the ECM reading it, and the ASD circuit was working correctly by plugging it in, turning on the key, and waving the CKP in front of the body, and the fuel pump would continue to run.

After another exasperating half day of flailing on this, I went in for lunch. While explaining what was going on to my GF, I had an ah-ha moment. Everything seemed to work fine, UNTIL cranking it over.

So, I'm thinking I must have a short somewhere that only happens during cranking. I most definitely did.

After getting the motor in and starting to hook everything up, I realized that after more than year, that I couldn't remember exactly where everything went. So, you start looking at where the various connectors and such want to naturally lie, as they tend to take a bit of a "set" after 20 years in the engine bay. So, I have one set of wires hanging down below the oil pressure sender, that line up pretty well with the two posts on the starter, but I can't tell for sure which one goes to which post. So, I hook them up the way that makes the most sense.

Weeks later, my truck still doesn't run and I am staring at it wondering if my starter solenoid has some internal short or something, so I disconnect all the wires to pull it out.

Then I realize that those same two sets of wires probably also will reach the two big GROUND studs on the side of the block.

I do some cautious testing of connecting them to ground (with a fuse between), and turn the key. VROOOM. (Insert 20 minute string of four letter words and throwing of small hand tools).

So, basically when the starter solenoid engages, and connects to the second terminal on the solenoid- I have been backfeeding 12v+ into the grounds for the TCM, ABM, and (I think) coil.

With everything hooked up the way it SHOULD be, everything seems to work fine. I had a couple codes for the TPS, but I think I have that figured out too. How it didn't nuke all the computers, set off the airbags, and go up in flames the first time I tried to crank it, I don't know.

But, she is alive, and I will start gently trying to get it broke in, and cross my fingers that everything keeps working.

Dumbass.

Thanks to everyone who offered suggestions.