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Mystery wires to transmission

D

desertdog2

NAXJA Forum User
Location
SoCal
I have a 1990 RENIX Jeep. I've had a problem with it running rough in gears other than 1. There are two un-connected wires (yellow/black strip and black/red stripe) hanging on the left side of the transmission. Wires go to the two sensors and I see nothing to connect these to.
I have noticed it will run right for awhile if I twist these two wires together.
Also, if I touch my battery terminals together it will run good for a short while.
It seems apparent these are some sort of feedback to the ECU. The trans is an AW4 that was rebuilt last January. I don't actually know if it's the original for the Jeep or a different rebuilt unit they tossed in there. If I unplug the TCU it runs great in 1, like a turd in 3 or D. Basically the same thing as with the TCU connected. The Power/Comfort switch IS working. I am hoping someone knows exactly what I need to do to resolve this issue.
 
I'm not sure what those wires are. Are they possibly for something further forward like the O2 sensor or the knock sensor? The trans computer has no connection to the engine computer, so its unlikely that anything with the trans or its wiring will cause the engine itself to run poorly.

This is a 4.0l engine, right?
 
It is a 4.0 I6. And there are speed sensors which do feed back to the TCU and or ECU. The fact that I notice a difference when I connect them seems a good indication it is related. But honestly, I don't know. It's not the 02 or knock sensor.
 
Additionally, these two wires come down in the same loom as two others connecting to the forward sensor on the trans, and the rear sensor has wires into it as well.
 
desertdog2 said:
Additionally, these two wires come down in the same loom as two others connecting to the forward sensor on the trans, and the rear sensor has wires into it as well.
Click to expand...

Forward sensor? For a 1990 tranny, there should be a harness that goes in on the lower side drivers side, mideway of the length tranny for the wires controlling the solenoids. There should be a pair of wires that go to the output shaft speed sensor that's hidden under the xfer case linkage mounting plate near the back on the drivers side. On the passenger side, there is the NSS sensor that gives the TCU feedback on what gear the shifter is in, and controls the starter interlock and backup lights.

If you're seeing a sensor on the drivers side near the front edge, halfway up I suspect you have a transmission transplanted from a 1997+ Cherokee. Those had an extra front input shaft speed sensor, as well as some differences in the rear sensor that would have to be sorted out to work with the older trans computer.

The ECU has it's own vehicle speed sensor which goes in the output from the xfer case (or the tailcone of the tranny if its a 2wd).
 
lawsoncl said:
Forward sensor? For a 1990 tranny, there should be a harness that goes in on the lower side drivers side, mideway of the length tranny for the wires controlling the solenoids. There should be a pair of wires that go to the output shaft speed sensor that's hidden under the xfer case linkage mounting plate near the back on the drivers side. On the passenger side, there is the NSS sensor that gives the TCU feedback on what gear the shifter is in, and controls the starter interlock and backup lights.

If you're seeing a sensor on the drivers side near the front edge, halfway up I suspect you have a transmission transplanted from a 1997+ Cherokee. Those had an extra front input shaft speed sensor, as well as some differences in the rear sensor that would have to be sorted out to work with the older trans computer.

The ECU has it's own vehicle speed sensor which goes in the output from the xfer case (or the tailcone of the tranny if its a 2wd).
Click to expand...

I'm not even sure if the Renix has a speed sensor that feeds the ECU. I tore the speedo cable out long ago and just use a GPS and my ECU never hiccuped. I'd have to look in the big renix book.
 
lawsoncl said:
Forward sensor? For a 1990 tranny, there should be a harness that goes in on the lower side drivers side, mideway of the length tranny for the wires controlling the solenoids.
check
There should be a pair of wires that go to the output shaft speed sensor that's hidden under the xfer case linkage mounting plate near the back on the drivers side.
check
On the passenger side, there is the NSS sensor that gives the TCU feedback on what gear the shifter is in, and controls the starter interlock and backup lights.
and check

If you're seeing a sensor on the drivers side near the front edge, halfway up I suspect you have a transmission transplanted from a 1997+ Cherokee. Those had an extra front input shaft speed sensor, as well as some differences in the rear sensor that would have to be sorted out to work with the older trans computer.

The ECU has it's own vehicle speed sensor which goes in the output from the xfer case (or the tailcone of the tranny if its a 2wd).
Click to expand...

ok so are you saying it reads from the speedo output? which is analog in this case. seems like changing gear ratios and tires would promptly eff that up...
when i say forward i mean the ones in the middle which you reference are solenoid controls. so what are these extras?
 
lawsoncl said:
Forward sensor? For a 1990 tranny, there should be a harness that goes in on the lower side drivers side, mideway of the length tranny for the wires controlling the solenoids. There should be a pair of wires that go to the output shaft speed sensor that's hidden under the xfer case linkage mounting plate near the back on the drivers side. On the passenger side, there is the NSS sensor that gives the TCU feedback on what gear the shifter is in, and controls the starter interlock and backup lights.

If you're seeing a sensor on the drivers side near the front edge, halfway up I suspect you have a transmission transplanted from a 1998+ Cherokee. Those had an extra front input shaft speed sensor, as well as some differences in the rear sensor that would have to be sorted out to work with the older trans computer.

The ECU has it's own vehicle speed sensor which goes in the output from the xfer case (or the tailcone of the tranny if its a 2wd).
Click to expand...
Corrected the year split, and the ECU VSS is on the output of the transfer case on 91+ models. 90- models, the ECU VSS is on the speedo cable and is only used for cruise like 87manche said.

There is no rear O2 sensor on RENIX XJs so it's not that.

They come down on the left, near the front sensor on the tranny... I am guessing you are talking about the CPS when you say that.

Perhaps the wires go to the coolant temp sensor (on RENIX, below the exhaust manifold on the side of the motor) or the knock sensor (unlikely, since that is on the passenger side of the rear of the head.) If it isn't those, I am well and truly stumped.
 
Ya got me stumped. The colors don't seem to match anything in the wiring diagram that I'd suspect like the coolant temp sensor or the tranny wiring. Maybe a picture would help us?
 
ehall said:
Those are used with the full-time and part-time light switch on the NP242 transfer case. A different pair of wires are used with an NP231.
Click to expand...

and in a renix year XJ they're not used for anything, it's all vacuum for the lights and CAD.
 
it's a 231 t case. did they even have a 242 pre 91? It's a laredo, so i suppose that's a possibility. In which case, they are null? It's a CAD axle, although I'm going to put in a one-piece shaft and get rid of all that vacuum nonsense.
 
desertdog2 said:
it's a 231 t case. did they even have a 242 pre 91? It's a laredo, so i suppose that's a possibility. In which case, they are null? It's a CAD axle, although I'm going to put in a one-piece shaft and get rid of all that vacuum nonsense.
Click to expand...

Yes, some RENIX era XJ's had the 242 case and non-disco D-30.
 
Found it. The Blk-Red wire is for the mechanically actuated 4WD switch for the Selectrac. The Yellow-Black is for the vacumn actuated switch for the CommandTrac track. Grounding them should turn on the 4wd light in the dash. They go to different pins on the instrument panel connector, so maybe the lights are different. Connection them together to make the engine run is probably just wishful thinking.

Aren't you missing a few pieces in that picture? Like the mounting plate and the xfer case linkage? Maybe that's why you didn't notice the lack of a working 4wd dash light?

Edit:
Of course, now I see the link eHall just posted http://www.naxja.org/forum/showthread.php?t=970403
 
you rock! yeah, I think it was a combination of wishful thinking and coincidence that made it seem like it related to my engine issue. Regardless, I am happy I know what they are now. I do have one more question: My part-time light seems to be related to vacuum, as it will come on/go off depending on whether I am in the throttle or not. Does that mean I have a vacuum leak? Also, when I change out my right axleshaft and get rid of the vacuum shifter, is there a good way to rig up my 4x4 lights so they work?
 
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