AW4 electrical problem?

I have a 1990 jeep xj with the 4.0 and the aw4 behind it. I just dropped a new motor in not to long ago and it runs fine. Recently i would drive it and it seems like it would shift into neutral out of no where no matter what gear it was in. I would pull over, put it in park, let it set for a minute, throw it into drive and it would work ok from any where from 10ft to 10 miles. So i did some reading and found out if its a electrical problem disconnect the tcu and shift manually. I did that and no problems at all, drove for about an hour not one slip. Last month i pulled off the pan and changed the filter and the fluids. It seems is shifts better but it still slips when the tcu is plugged in. I pulled the pan off again and this time i checked the shift solenoid voltages and they all were in the good range according to the manual. I double checked my tps and that is right where the voltage should be. Last week i did a line pressure test on it and all of the pressures seemed to come out in the normal range according to a aw4 manual i got. I cant really figure out what it could be unless one of the shift solenoids may be plugged up with something. Has anyone else had this problem?

You said you checked the voltages at the solenoids, but did you check the ohms?

Good reference here: http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html

You checked the TPS and the output voltage was 83 percent of the reference voltage?

Did you adjust the throttle pressure cable? http://naxja.org/forum/showthread.php?t=1015963

joe_peters said:

You said you checked the voltages at the solenoids, but did you check the ohms?

Good reference here: http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html

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sorry about that i did check the ohms.

Check the resistance of the solonoids. you could check thak by unplugging the harness and measure at the harness. Also check all wire connections. They should be clean and tight. The NSS (Neutral Start Switch) could also be the culprit. I am not sure the TV cable would cause it to go into neutral so to speak. The TV cable is more mechanical rather that electrical.

First thing that comes to mind is that if a solenoid doesn't work won't get neutral. You didn't say how fast you are going. Could it be that the trans is going into OD and since you are going slow the trans is just slipping and it feels like Neutral? With the TCM unplugged put the trans in OD and try to take off, is this the same thing? The TPS, VSS and other external electrical components are usually the root cause of AW4 issues. So with all that being said you could get two toggle switches and jumper them into the trans plug and then shift the trans manually to see if with non TCM power to the solenoids the trans shifts OK.

R.DesJardin said:

First thing that comes to mind is that if a solenoid doesn't work won't get neutral. You didn't say how fast you are going. Could it be that the trans is going into OD and since you are going slow the trans is just slipping and it feels like Neutral? With the TCM unplugged put the trans in OD and try to take off, is this the same thing? The TPS, VSS and other external electrical components are usually the root cause of AW4 issues. So with all that being said you could get two toggle switches and jumper them into the trans plug and then shift the trans manually to see if with non TCM power to the solenoids the trans shifts OK.

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i usually drive on a 35mph road. (still doing some work) I have tried putting it into od with the tcu unplugged and taking off and it feels nothing like what it does when it drives. When it drives it shifts at normal shift points. It doesnt matter what gear it is in, it will actually feel like its in neutral in which i mean, It will rev up, you can hit the gas and it wont get a grab and go.

techno1154 said:

Check the resistance of the solonoids. you could check thak by unplugging the harness and measure at the harness. Also check all wire connections. They should be clean and tight. The NSS (Neutral Start Switch) could also be the culprit. I am not sure the TV cable would cause it to go into neutral so to speak. The TV cable is more mechanical rather that electrical.

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never tried the neutral start switch. ill try to find out on how to check that.

i checked by tv cable even though that would be a mechanical problem. Seems to be fine. tommorow im going to check my harness and check the neutral start switch.

Tranny fluid level and condition?

the tranny level is in the normal range when at operating temperature, its new fluid, but even when i changed the fluid when i did the tranny filter it didnt smell burnt or didnt have any odd color.

i tried the neutral start switch, it only starts in neutral and park. Other than those two it wont start.

does anyone know a way to check if your tcu is actually functioning correctly? im still in the process of checking my wiring harness to the tcu, but i figured if nothing is wrong with the harness and everything comes out normal i would have to pretty much say its the tcu right?

Good News, and Bad News.

Good news is the 1990 TCU stores codes and has a self-diagnostic! Bad news is you need a DRB II scanner to check it.

That means DEALER. Might be cheaper to pickup a TCU at the salvage yard.

whammy said:

does anyone know a way to check if your tcu is actually functioning correctly? im still in the process of checking my wiring harness to the tcu, but i figured if nothing is wrong with the harness and everything comes out normal i would have to pretty much say its the tcu right?

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You could get a couple LED's jump them into the solenoid wires going from the TCU to the trans. watch the shift sequence as the lights turn on and off. At least you know a little more.