Djkd20q

Hi all, I have a 2000 Jeep cherokee sport, 4.0l 4x4 Aw4, we bought it cheap with cracked piston skirts, in running condition,swapped a known running motor in, and now have great fuel pressure, 50 psi, but no spark, and a No bu5 message on the console, also no gauges, I can unplug the tcm and regain gages and loose the no bhs message, but it still does not spark or start, it has a brand new, tested good (as did the original) mopar cps in it, have tried to unplug all engine management sensors, ckp, cps, coolant temp sender, oil press sender, map, tps, iac, and still have no spark, still have no bus, pin 3 to pin 11 of dlc reads 120 ohms with tcm unplugged, 69 ohms with it plugged in, with the tcm and pcm all plugged in, tcm pin 6 to c3 pin 28 reads .2 ohms, with batery unplugged, dlc pin 11 has continuity with tcm pin 6 (I believe) has continuity, what else can I do, I have removed door panels, airbag module, dome light, new pcm (3 of them known to be good)(1 known to be good tcm), It has factory rke, that is removed, If I cannot fix this in the next week Im gonna send this to my buddys boss who is a jeep electrical guru, hed probably do it for free, but I will pay him something, so Id rather do it myself and learn in the process.

Djkd20q

Oh, and the scanner cannot communicate with the tcm plugged in, but without it plugged in it pulls a p1698 code

Djkd20q

CCKen maybe?

Djkd20q

Pcm C3 pin 30 has continuity to tcm pin 7, Pcm C3 pin 28 cas continuity to tcm pin 6, those are the CCD Bus + and - circuits, so I have to be left with a shorted engine module right?

CCKen

Did you measure the CCD Bus voltages at the DLC (3 to 4/5, and 11 to 4/5) with the TCM plugged and with it unplugged?


Sounds like the TCM may be corrupting the CCD Bus, or it has a bad input(s) that are corrupting the TCM.


Do you have Sentry Key Immobilizer System? If you do see if the amber SKIS graphic in the upper left corner of the instrument cluster is on steady when you try to start the engine.


Seems strange that with pin 3 to pin 11 of DLC reads 120 ohms with TCM unplugged, 69 ohms with it plugged in. I would think it would be just the opposite - if anything. There are termination resistors in the PCM and the instrument cluster. If one of the termination resistors are gone you should see 120 Ohms and with both resistors line you should see 60 Ohms. 69 Ohms is too high.


Measure the 5 volt supply voltage to the engine sensors at any sensor, like the TPS, at the connector Orange wire with the key to RUN/ON. Should be 5 volts +/- .5 volts.

Djkd20q

I do not have SKIS, have a black key, not the fat chipped gray one, 3 to 4 on dlc is 2.38 I think, 11 to 4 is 2.41 I believe, though those two voltages could be reversed, the ohm readings could be off, cause only those were measured with a meter with a dying battery, I will take dlc voltages with tcm both unplugged and plugged in, and re test ohm reading, tps voltage,in a few hours, thank you so much for your help!

Djkd20q

Also found out today witt or without my overhead lights and I assume rke circuit board connected, my unlock buttons only make the pass. door click, and my rke does nothing.
DLC pin 3 to pin 4 is 2.42 tcm unplugged, is 8.97 tcm plugged in
DLC pin 11 to pin 4 is 2.41 tcm unplugged, 8.99 tcm plugged in, all of those readings are with the meter set at 20 vdc, only option for dc on meter, and tried anothsr known good tcm and got the same readings with it plugged in



DLC ohm readings pin 3 to 11, key off, tcm unplugged is 60.3 ohms, tcm plugged in is 70.5


Tps sensor voltage is 5.22, key on, tcm plugged in, map is also 5.22


All readings are in 20vdc range, or the 200 ohm resistance range

I appreciate any and all help you guys on here give me, mainly you CCKen, forums like these are a huge part of what makes jeepin' what it is

CCKen

"DLC pin 3 to pin 4 is 2.42 tcm unplugged, is 8.97 tcm plugged in
DLC pin 11 to pin 4 is 2.41 tcm unplugged, 8.99 tcm plugged in, all of those readings are with the meter set at 20 vdc, only option for dc on meter, and tried another known good tcm and got the same readings with it plugged in"


The CCD Bus readings with the TCM plugged in are wildly off scale.


You may have a bad input to the TCM making it look like its bad.


Suggest you do the tests on the TCM inputs (below) to see if you can find the bad guy(s). Do all the tests even if you find something wrong right off the bat.


Read through both pin out and test procedures before beginning.


I recommend using a safety pin as a probe.



.

Djkd20q

I assume I am checking for continuity between those points and the red ones listed next to them? Sorry if its obvious, I understand wiring diagrams, but not always diagnosing them, I will go try this stuff, thank you so much for your effort, this jeep was about to be in the scrap yard.

CCKen

The red text in the pin out diagram are my notes to give some insight as to what is associated with the pin cavs.


You will be check for voltages on some tests and continuity/resistance on others. Read the test procedures completely first.


Sometimes troubleshooting can be a PITA but can save you a few bucks in the long run.

Djkd20q

Ok, I think we may have found my (our) problem,
Restistances
Cav1-Cav2 600 ohms resistance good
Cav3-Cav4 600 ohms resistance good
Cav7-Cav6 60 ohms resistance good
Cav24-Cav11 14.9ohms resistance good
Cav24-Cav12 15 ohms resistance good
Cav24-Cav13 15 ohms resistance good

Voltages are where the real problems started, I noticed if I had my negative probe in Cav24 and touched the positive to any part of my body it read battery voltage, also Cav24 of tcm to pin 4 of the dlc read battery voltage, I found this odd, I thought that would read 0vdc, both being labeled ground.
Voltages
Ign lock Cav24-Cav25 -.06vdc
Ign on (I had this in run position)Cav24-Cav26 -.12vdc
Shifter in reverse Cav24-Cav18 -1.41vdc
Shifter in drive Cav24-Cav22 .00vdc, nothing, zip, nada
Shifter in 3rd Cav24-Cav9 -.04vdc
Shifter in 1st-2nd Cav24-Cav21 -.04vdc
Cav17-Cav16 Idle .98vdc
Cav17-Cav16 Wot 3.86vdc
(the tps I swapped from my other jeep, I already knew it is a little out of range, not sure if that has an effect on these readings)
Cav6-Cav24 -7.28vdc
Cav7-Cav24 -7.26vdc
These tests were all conducted using Cav24 as ground, so the negative voltages are really striking me as odd.
Without you I would not have discovered any of this, so I really do thank you for your help.

CCKen

Not good. I think you should address each ground point in the engine bay by disassembly, scrubbing the ring terminals clean, then reassemble securely




I have to check out now (the wife you know) otherwise I would post pics.

Djkd20q

Thank you for that, I will do the ground terminals tomorrow and get back with you, I hope it is one of them, if not I will ask you I guess

CCKen

What year engine did you swap in?


If you still have issues with the voltage readings using pin cav 24, try using the gas pedal bracket stud/nut as the ground for your meter. You can also check continuity of the TCM ground from 24 to engine ground G101 using the gas pedal as the meter ground. See pic.


G101 is the ground for the TCM and PCM. See pic.


Seems odd that you would get negative (-) voltage readings. If the meter probes are reversed you will see negative numbers.


Gas Pedal:





G101: 99 shown with a coil. Of course, the 2000 won't have a coil at this spot but the ground functions are the same.



.

Djkd20q

Ok, I used mini paper clips as test probes so as not to damage the pin cavities, last night after I last replied to this thread I put one in cav24 of tcm, and on in cav 5 of dlc, tcm ground and pcm ground, when I touched a wire to the two it sent off a spark and blackend that arc spot on the tcm paper clip, so I attempted again using dlc pin 4 instead, got the same spark, so I did it again on dlc pin 4, except this time I held it there for maybe 3 seconds, the paperclip turned red hot, melted in the middle, and when I pulled the wire off, the paper clip end fell and cooled, turning it from a straigh paper clip to a 90, I thought that pcm and tcm and plain ground share the same grounds, something must be feeding voltage into tcm ground correct? Tcm cav24 to gas pedal stud showed 150 ohms, way more than the 5 ohm threshold.

Engine swapped in is also from a 2000, has a coil rail.

I can check grounds later tonight, for a large part of the day today I will be at the local hospital getting my thyroids checked out.