jmsjokerhaha

91 xj 4.0 straight 6. Sorry its long but I want to be very specific...
My XJ will not up shift past 1st gear. If I unplug the TCU for a minute and plug it back in it shifts fine for 15 min., then back to not shifting out of first gear. If I unplug the TCU and leave it unplugged, I can shift manually 1-2, 3, 4. I have replaced the TPS sensor and Checked the voltages on the new one, .80 idle 3.80 wot. I have Tested the TCU its getting 12 volt supply, and the .80-3.80 TPS signal, and I test the solenoid pins on the TCU with the TCU plugged in I get 9.40 ohms on all three solenoids If I test the pins on the harness with the TCU unplugged they all show zero ohms. I tested my speed sensor by having my girlfriend hold the ohm meter while I spun the drive axle and watched it say some random readings (I do not know how else to test it). I have also tested the resistance between the pins on the NSS harness they all test to have perfect continuity when in the correct shifter positions. Next was to try a new TCU bought one on ebay and it behaves exactically like my old one working fine for 15 min. then not shifting out of first unless I unplug the TCU for a min. then everything works for another 15 min. and then the cycle just keeps going and going. What am I suppose to try now? A new ECU? It looks to me like the ECU in my jeep now was a replacement bought from a wrecking yard or something by the previous owner. This is my first jeep and after working on it for months now with no luck I am seriously considering throwing in the towel and selling it.

VTJeep

That really sucks man. You've clearly spent some time and subsequently money, I'm sure, trying to solve this. It would really suck of it was the ECM. I know mine new is like 340 bucks.. I'd still be a little leery of the eBay TCU, but other than that, idk...
I've been there with wanting to get rid of the jeep. Had, and still have, an intermittent hesitation issue. Bought in 07/09 and have had the issue, though far less often, ever since. But, I sorta pushed thru it, and in all honesty, the issue bugs the hell outta me, but there's no way I wanna give my XJ up now. I've seen what it can do when runnin right and I'm totally hooked... Good luck man.

Radi

Are you getting 12 volt solenoid shift voltages out of the TCU when it fails? Solenoid 1= 1st gear, solenoids 1&2 = second gear, solenoid 2 = third gear.
One or more input or output signals dropping out after 15 minutes?

To test the speed sensor I use an oscilloscope. It puts out a square wave. For your year It's a simple reed switch that closes once each revolution of the output shaft.
If it's stuck open or closed you're TCU-locked in first gear.
You may be able to test it with an ohmmeter if you can somehow spin the output shaft slowly by hand. You should see clear switching from zero ohms to infinity and back.
You might also be able to see the switching by creeping forward very very slowly...never tried it though.

I am also very leery of an Ebay TCU. I'd prefer one from a scrapyard, lol. Less than scrupulous people Ebay their junk, and this is a common failure mode for the TCU. One or more of the solid-state solenoid drivers heats up and fails. Sometimes the failure is permanent, other times intermittent. You may have the latter. See above about checking for missing or low solenoid voltages when it fails.

One cause for a failed TCU solenoid driver is a solenoid that drops resistance while operating, often partially shorted.
It pulls too much current, overheating the TCU driver which shuts down. Pulling the plug resets it.
It should read no less than 11 ohms after operating for a while, 12-15 is typical. Problem is the 1.5 volts out of a typical ohmmeter isn't enough to lock it in and heat it up, it only acts up in operation.
Also check the TCU => Solenoid wiring harness for chafing, bad connectors or other problems, and for a good ground connection to the TCU and the transmission case.

If all else fails, the TCU does store some trouble codes which may be useful, although you need a DRB-II reader to retrieve them. Chrysler dealers have access.

Don't give up just yet...the transmission proper is OK since you can shift manually, this is an electronic problem.

jmsjokerhaha

I have 12v supply to c16 that goes to solenoid number 1 and I managed to go on a test drive with the ohm meter hooked up to my TCU and I got 13.5 volts at c15 whenever the car shifted out of first I looked over at the ohm meter and it said 13.5 volts then when I would stop at a light it would go to zero volts. I would assume when It dosnt shift that i will not be able to see a volt reading from c15 because I only got a reading when it shifted out of first. I am clueless how to test if the 12 volt supply to the solenoids drops out when it stops shifting, because I wont be able to get it to shift automatically...I also have no idea how to test the resistance on the solenoids other than dropping the pan witch I guess at this point I am going to have to buy a new gasket kit just to open it up and look.

armando572

Hi, I have the same problem in my 97 cherokee 4.0L. After about 10 minutes running converter starts not to lock up, and a few minutes later it starts to shift erratically. It downshift to 2 when it should be in 3 and when shifting from 3 to 4 it goes into neutral unless i accelerate to about 4900 rpm. When i disconnect the tcu it shifts properly. I have replaced the filter. I have checked all solenoids and they give good ohm readings. I have checked the TPS and gives good readings, but just in case i have replaced it. I have replaced the TCU, the ECU and even the transmission itself and i still have the problem. Every time I disconnect the battery or the TCU it works good for about 10 minutes but then it starts to shift erratically again. Any suggestions? Also, how can i test the TCU removed from the vehicle?

jmsjokerhaha

I found an awesome tranny shop in town that had a drb11 scanner and scanned my jeep for codes for free. no codes the guy said maybe when I shut off the engine it cleared the codes so I came back when It acted up again and left it idling still no codes. He hopped in my jeep with the scanner plugged into the TCU and said the only thing the didnt seem 100% right was the readings for the input speed sensor. I had already replaced the output speed sensor that is easily accessible on the rear of the tranny. He showed me the location of the input sensor it is hidden behind a bracket that holds the shifter lingage arms to the left side of the tranny closer to the front, and also printed me out a little diagnostic tree to test if the wires from the TCU to the speed sensor were bad (he did all of this for free!)The bracket has to removed to get to the sensor. I tested the wiring and it seems fine no shorts, no one in town had it and the cheapest I could get it was 100 bucks online. Its in the mail now should be hear tomorrow and I will post letting you guys know if that fixes it.

Rustydog555

Bet that works I had a similar problem very interment at first just like a TPS acting up or out of adj spent way to much time messing with the speedo and cruse controls speedo before I found that speed sensor had a used trans sitting around switched em out like new. And you can r&r without removing the bracket if you are willing to grind a little off the bracket to get the bole back in