AW4 experts...what's going on ?

Ok, my jeep has been acting weird the last year, almost like the tranny is shot. It is a 350K old AW4, with 31's, and I assume 3.55 gears. Fluid is red and doesn't smell burnt.

It drove fine with 30's for the past 5 yrs, but when I put on the 31's last year, it started acting this way. MPG is also way down, but part of that may be 350k injectors and a cracked exhaust manifold.

Problems are lousy mpg & acceleration, and to get it to downshift, you have to literally push the pedal thru the floor and hold it.

The throttle cable has been adjusted and readjusted based on many posts here.

Most of the TPS readings are good, but the resistance on the ground side is high. I am going to do some more checking on these readings tomorrow.

I drove it tonight to do some trouble shooting and get some info, and here's the results: (all speeds are GPS)

TCU connected - 60 mph nets 1950 rpm, it does seem the TC is locking up, but not sure OD is working

TCU disconnected - 60 mph nets 1950 rpm in 4th gear
TCU disconnected - 60 mph nets 2550 rpm in 3rd gear
TCU disconnected - All gears shift fine manually, but no 2nd gear as expected.

Using the grimmjeeper gear calculator, the rpm are high by 200-250, which is a bit much.

The tach I can deal with if it is off by that much, but the lack of acceleration/downshifting is a problem. Idle RPM in gear on the tach is 600 BTW.

I also noticed that about 2500 rpm in 1st gear, the acceleration really jumps when the TCU is disconnected. Not sure if this is an engine characteristic, or a trans issue.

So what is the guess ??

Well, your brake switch may be bad, which would cause the TCC to not lock up properly. I installed a TCC lockup switch in mine. And when I put my 31's on with stock 3.55s I disliked how it drove. Now I have 4.10s. I would say replace the TPS and see if anything changes.
As for accel, not sure how it is supposed to respond but since there is no 2nd gear with the TCU disconnected so seems alright.
When was the last time the trans fluid was flushed?

Fluid was flushed about 5 yrs, or 25k ago.

Talk to me about the TCC lockup switch. I may need to do that to bypass the brake switch, as when I put in the 96 GC booster, I had to put in a shim to get it to work right (that was 5 yrs ago).

Even if the TCC isn't locking up right, that wouldn't really explain the acceleration, but it could explain the higher than normal rpm @ speed.

Sounds to me like the brake switch or TPS is at fault. High resistance at the ground to it will give some screwy readings probably, and crummy brake switch function will result in the TCU thinking you are riding the brakes whenever the switch is jammed, which means it will not lock the torque converter.

EDIT: this is on the 88 in your profile right?

I am in the same boat. I washed my engine today and after that everything you just described is happening to me. I can not get it to kickdown while climbing a hill on the highway and accelaration is super slow. The really bad part about this is that I have a 4 hour drive I have to make twice a week, tomorrow is one of the days I have to drive. I adjusted the TV cable according to the FSM and that seemed to help a little but it just isn't quite right. I am going to test grounds on the TPS and adjust it if necessary in the morning. Other than that I am out of ideas, anyone else have any other suggestions?

was it doing it before you washed the motor?

If no, you almost certainly got water in your TPS. They are pretty sensitive to being hosed, if you wash your motor you should always cover the distributor with a plastic bag and avoid getting water anywhere near the TPS for this reason.

Tough to get water back out, too, it's usually easiest to replace the TPS.

Where exactly is the resistance in the TPS ground? Did you read it at the flat connector or the square one, and how much resistance?

My wife's 88 with 31s performs perfectly, just like stock but I did a few things to it.

First off, check to see if the "trans" fuse in the fusebox is blown. If it is, you will have no power to the Power/Comfort switch. That will make the TCU default to Comfort or "Grandma" mode as I call it.
If you find the fuse good, you could still have a bad Power/Comfort switch. Even if it lights up it can be bad. I remove the switch and unplug it. There are 3 wires in the harness plug. IIRC, one has a stripe, one is tan and one is black. Make a 4" jumper wire with male spade terminals on each end and connect it between the tan and the one with the stripe. Black is ground for the switch light. Don't do anything with that

I have also found that the TV cables have stretched beyond the adjustment that was built into them. I have tweaked the bracket that holds the cable closer to the valve cover slightly to get the adjustment where I want it. Do this last. Be absolutely sure you have the TCU in Power mode first.

Yes, this is on the 88 cherokee, not my 96 (I wish the 88 drove and shifted like the 96 ! Sometimes it is hard to believe they have the same drivetrain)

OK, the fuse looked good, but I didn't test it, and the light does light up. I use to always use it in power mode, but got annoyed by the light reflecting off the windshield on long evening drives.

Bypassing it defaults it to power mode then ?

And the ground, when I measured it, was in the 2.5 ohm range, instead of the .1 or less range.

And I have seriously considered tweaking the bracket for the kickdown, as I have been suspecting it may be stretched.

I am going to try and get some readings this afternoon, and will post back.

Ok so I just got done checking my TPS according to the sticky for testing them on the OEM section and the 3 wire connector is only getting like 1.6 volts for reference voltage. It has a good 5 volts going into it though when the plug is disconnected. The 4 wire plug on the side that controls the transmission has 4.64 for a reference voltage. Both of the grounds for it have less than 1ohm of resistance. I am really suspecting the TPS. Would anyone like to confirm this for me, I am getting ready to call the parts stores right now and see if I can find one.

TPS is definitely suspect.
Default your Power/Comfort switch as described above so that it's always in the Power mode.
Leave the connectors of the TPS plugged in and have the key "on" when testing the TPS. Backprobe the connectors.
Where are you getting 2.5 ohms resistance?
Did you use my TPS instructions? They're in a sticky above.

Ok, well I didn't mean to hijack this thread but since the problems were similar I figured we could collaborate the brain power and kill two birds with one stone.

I just finished installing the new TPS and adjusting it according to the sticky thread about TPS adjustment. Everything came out perfectly voltage wise and then I adjusted the throttle pressure cable according to the FSM one more time just to make sure everything was right on the nuts. It shifts perfectly now infact I think it is better than before.

TRCM I would reccomend cleaning up your grounds and or possibly making new ones for your TPS if the old ones just can't get right. After you get your ground issue fixed follow the steps contained here: http://www.naxja.org/forum/showthread.php?t=1072534 if your voltages aren't coming out right or they aren't smooth you might be in the same boat I was and you will be replacing the TPS. I just got one at Auto Zone for 39.99 with a 2 year warranty. I can see how easy water was able to get into the TPS so I somewhat waterproofed my new one with some RTV in hope that it can help keep the water out. I have always washed my engine everytime I go to the carwash and I am not going to let a little sensor stop that for me. Good luck on the troubleshooting, let us know what you figure out.

I would not use RTV on a TPS, but load that thing up with dielectric grease to your hearts content.

Also, as a side note - manual transmission TPSes for RENIX years are very expensive, if you ever end up working on a manual RENIX that needs a TPS, just install an auto one instead and save ~$80.

cruiser54 said:

TPS is definitely suspect.
Default your Power/Comfort switch as described above so that it's always in the Power mode.
Leave the connectors of the TPS plugged in and have the key "on" when testing the TPS. Backprobe the connectors.
Where are you getting 2.5 ohms resistance?
Did you use my TPS instructions? They're in a sticky above.

Click to expand...

Yes, I used your instructions when I did it.

The 2.5 ohms was between the ground on the TCU tps connector and the battery.

I didn't get to check things this afternoon, but will this week. Called mom & dad and ended up talking to dad, who's about to retire, about what truck he should get & why for almost 3 hrs or so.

bigsky said:

I am in the same boat. I washed my engine today and after that everything you just described is happening to me. I can not get it to kickdown while climbing a hill on the highway and accelaration is super slow. The really bad part about this is that I have a 4 hour drive I have to make twice a week, tomorrow is one of the days I have to drive. I adjusted the TV cable according to the FSM and that seemed to help a little but it just isn't quite right. I am going to test grounds on the TPS and adjust it if necessary in the morning. Other than that I am out of ideas, anyone else have any other suggestions?

Click to expand...

You might try soaking (dip) or washing the TPS in 90% IPA (Isopropyl Alcohol, from the pharmacy), then dry it out at 250 F in a bake oven.

Is there a way to bypass the brake switch input on an 88 ?

I am sure there is but don't have my renix fsm in front of me. It would be either disconnect the switch or shunt two of the pins, not sure which.

Well, I finally got some time to work on this

1) cleaned the c101 connector (nasty tar everywhere)
2) bypassed the power/comfort switch
3) tweaked the kickdown cable bracket to account for stretch

Reference voltage at the TPS is now 4.6v, output is 3.8v, and grounds are less than .1 ohms

Now, it seems to shift fine, has a decent kickdown, but still no lockup.

Checked/cleaned the upper brake switch, and it is doing it's job, sending 12+ volts to the TCU when brakes are applied.

What next ?

hmmmm... I would set up a manual torque converter lockup switch just to see if it works. If it does, you know it's not the solenoid, and now you have a lockup switch. It's pretty easy - take an SPDT switch, cut the wire from the TCU to "solenoid C" or the torque converter lockup solenoid depending on how your manual describes it. Common pin on the SPDT switch goes to the cut wire going away from the TCU, NC goes to the cut wire going to the TCU, NO goes to an ignition switched +12V source. Turn the switch to the ON position to force lockup, turn it to OFF to let the TCU control it itself.

You can also unplug the TCU and set up a test switch to the solenoid C/lockup wire in the connector (other end goes to +12V) and then drive it shifting manually and using the lockup switch.

If it locks up properly using any of these test methods the torque converter, lockup solenoid, and all transmission internals are fine, and it's some variety of electrical issue.

First of all, excellent job tackling this.

The TCU itself grounds at the engine dipstick tube stud as does a separate circuit from the TCU called the "Shift Point Logic" circuit. If you haven't already, I would remove all the ground terminals from that stud, make sure there is bare metal at the stud and it's not loose, clean til shiny all wire terminations, re-crimp the terminals, and reattach securely.

Over by the trans dipstick there are 2 fairly large square connectors. One is black and the other is gray. Unplug them and inspect for any corrosion and/or bent pins. Spray them out with electronics cleaner, add some dielectric grease and reconnect.

Couldn't hurt to also remove or unplug the TCU and give it's connection the same treatment.