Jeep 4.0 Automatic not changing gears.

[Gradinen]

Hello! 

I have an 88 automatic Laredo that has been sitting for about 20 years... I've just got it going again with the aid of the forum and such. 

I started to change the oils to check the status of the viechle, engine, trans and gearbox. 
Thing is, the gearbox won't change gears when I'm driving.

 

The gearbox doesn't change gears until I've reached about 60kmh, I let go of the throttle and it changes back into first gear at about 55kmh. 
I've tried to change gears manually by changing from 1-2 to 3 but nothing, doesn't matter at what speed I'm driving. 

I've checked the Kickdown wire. It doesn't look like its broken, its springy when I pull it and doesn't seem loose. Though, when I try to do the adjustment reset as many show in the videos on youtube, I move it all the way back and push the throttle. The kickdownharnessthing only changes a little bit with a click. The videos show a greater change then what happens to mine. 

What I recently did with the gearbox? Well, I took the pan down and changed the filter and the oil. There were not a single metal shaving on the magnets. 
I did a quick testrun when I first got the car going, and before I changed the oils.. I can recall that it changed between gears but brainghosts makes myself doubt myself a wee bit. I only drove about 20-30 kmh as I had my toddler with me in the car. 

As any amature I've consulted with AI and gotten the advice to either change the oil again, do some accelarations and hope it fixes itself, or its the govenor in the gearbox. Suggesting I remove it and clean it as dirt might have gotten into it. 

What do you pro comanche folks say? Anyone else had the same problem, or have a guess what might be behind the issue? 
Its a 3 gear gearbox on a 4.0 6 cylinder laredo. 

[89 MJ]

A 3 speed with a 4.0 you say? Does is the transmission computer controlled or is it just kickdown linkage? What type of transmission is it?

 

I don't think that you are from the US, but here in the US, all 4.0 Comanches with an automatic transmission came with the AW4 4 speed automatic. Other AMC and Jeep models could come with 3 speed autos. In AMCs, I know this was the TF998 in the late 70s. 

[Gradinen]

1 hour ago, 89 MJ said:

From what I can tell its only Kickdown linkaged, any way of telling its computer controlled? 
No, I'm from Sweden and was surprised myself that it was a 3 speed Laredo with the 4.0. 

 

[89 MJ]

Your English is very good. When you say the kickdown wire, it is just a metal cable inside a plastic sleeve, correct? Any chance you can take some pictures of what you're working with?

[fiatslug87]

Are you sure the fluid is at the correct level? Mine does that once in a while, I add a little fluid and then it shifts properly.

 

Please add your truck to the registry, your build sheet will be provided and trans identified. https://comancheclub.com/forum/31-1988/

[Gradinen]

1 hour ago, fiatslug87 said:

Are you sure the fluid is at the correct level? Mine does that once in a while, I add a little fluid and then it shifts properly.

 

Please add your truck to the registry, your build sheet will be provided and trans identified. https://comancheclub.com/forum/31-1988/

Yes, I thought that was the issue at first. 
I rechecked everything this evening. I drove the car, made the trans warm and parked it on a level surface, I filled from about just at the minimum mark on the stick to about right in the middle. No change at all. Perhaps there's a slight more noticable "clunk" when I put it into drive. 

[Gradinen]

1 hour ago, 89 MJ said:

Your English is very good. When you say the kickdown wire, it is just a metal cable inside a plastic sleeve, correct? Any chance you can take some pictures of what you're working with?

Thanks, the younger generation (90s) are pretty much forced to speak english in every day life if you're in the right trade. 

Yes, its just a metal wire in a plastic sleeve. I can fix a picture tomorrow! Thanks. 

[89 MJ]

32 minutes ago, Gradinen said:

Thanks, the younger generation (90s) are pretty much forced to speak english in every day life if you're in the right trade. 

Yes, its just a metal wire in a plastic sleeve. I can fix a picture tomorrow! Thanks. 

Perfect! I think we should also try to figure out what transmission it has. The Chrysler transmissions (like the TF998 that I suspect you may have) do not run the pump in park, so the fluid level must be checked with the engine running and in neutral.

[75sv1]

There should be a fuse for the transmission. You can pull that. Then see if it shifts manually. If it does, then its electronics. Then you should check the ohms of the solenoids. There would be three of them. 13 ohms +/-3. There should be a plug up by the trans dipstick, to access the wires. The other is the speed sensor. Yours should have one. I haven't worked on the earlier autos.  Should be a hall effect sensor. On or Off. You need an analog Volt meter with ohms. The connectors are also on the same wiring connection up by the trans dipstick. You need to turn the shaft of the transmission. 

[Gradinen]

18 hours ago, 89 MJ said:

Perfect! I think we should also try to figure out what transmission it has. The Chrysler transmissions (like the TF998 that I suspect you may have) do not run the pump in park, so the fluid level must be checked with the engine running and in neutral.

Unfortunately no change, I checked the oil again today and no difference when in neutral. 
 

 

[Gradinen]

21 hours ago, 89 MJ said:

Your English is very good. When you say the kickdown wire, it is just a metal cable inside a plastic sleeve, correct? Any chance you can take some pictures of what you're working with?

Here it is! 
I manually pulled the inside of the harness to the right to adjust it today, as I've seen videos where the self adjustment does way more then it does when I do it. 
What happened was that the car lost power near 60kmh and didn't shift.. I re adjusted it as it is now and it shifted again only at 60+ kmh. 

[89 MJ]

Seeing that, I would assume it is somehow out of adjustment. I wish there was an easy way that we could figure out the type of transmission you have. 

[derf]

One question I have.

 

On the shifter, is it 

 

P

R

N

D

2

1

 

Or 

 

P

R

N

D

3

1-2

 

[Eagle_SX4]

@Gradinen can you get under the vehicle and take a picture of the transmission. It should be easy to figure out which transmission you have with a picture.

[Gradinen]

On 4/16/2026 at 6:48 PM, derf said:

One question I have.

 

On the shifter, is it 

 

P

R

N

D

2

1

 

Or 

 

P

R

N

D

3

1-2

 

Its the latter, 1-2 3 D N R P 

[Gradinen]

Update. 

I've changed back to the old oil filter today, no change. I manually changed the Kick down to somewhere in the middle. Now the car looses power near 40 kmh, it rews down in rpm and it feels like it tries to find a new gear but it doesn't. When driving downslope I can get past it and its the same symptome. It only changes gear until I'm near 60 Kmh. 

[Eagle]

The factory service manual recommends checking transmission operation by shifting manually. It should shift from first gear to third gear if you start with the shifter a "1" and then manually move the shifter to "3." If it doesn't shift, then there may be a problem with the solenoids. The AW-4 shifting is controlled by solenoids. If they don't work -- it won't shift.

[llhat]

Partially true,  the AW4 when controlled by the TCU does shift through the solenoids, 

when using the column lever, the shifter engages a manual valve, shifting the 'gears', but no overdrive (4th) or 2nd, or the converter lockup.

 

what happens if the OP tries to start movement in "D",  if there's an issue with electronic shifting, the transmission will try to start in 3rd gear and it won't like it.

 

[Gradinen]

On 4/15/2026 at 1:08 PM, 75sv1 said:

There should be a fuse for the transmission. You can pull that. Then see if it shifts manually. If it does, then its electronics. Then you should check the ohms of the solenoids. There would be three of them. 13 ohms +/-3. There should be a plug up by the trans dipstick, to access the wires. The other is the speed sensor. Yours should have one. I haven't worked on the earlier autos.  Should be a hall effect sensor. On or Off. You need an analog Volt meter with ohms. The connectors are also on the same wiring connection up by the trans dipstick. You need to turn the shaft of the transmission. 

Tried this today, there's no difference with or without the fuse. 

 

[Gradinen]

8 hours ago, llhat said:

Partially true,  the AW4 when controlled by the TCU does shift through the solenoids, 

when using the column lever, the shifter engages a manual valve, shifting the 'gears', but no overdrive (4th) or 2nd, or the converter lockup.

 

what happens if the OP tries to start movement in "D",  if there's an issue with electronic shifting, the transmission will try to start in 3rd gear and it won't like it.

 

When I start in D it remains in 1. Now it starts to try to shift gear in about 40kmh but really doens't mannages. : /

[Ωhm]

Aren't there two fuses for the TCU? One in the fuse panel (7.5A) and one inline (15A).

[llhat]

yes,  but think the in-line is 10a,  located near the TCU mounting location under the lower dash panel.

[llhat]

3 hours ago, Gradinen said:

When I start in D it remains in 1. Now it starts to try to shift gear in about 40kmh but really doens't mannages. : /

Memory of 'my' issue...  and @ohm's help...   The Solenoid for 1'st gear is being energized if you start out in D and the vehicle readily moves...
I drove mine for some time manually shifting the gears,  just not getting overdrive and remembering to shift down at stops.

 

the non shift could "possibly" be in the TCU,  not instructing the gear 2 solenoid to energize....  I would have to go back and study the posts between Ohm and I and review some of the wiring diagrams..    there is no board level diagram for the TCU.

 

would suggest testing the solenoids for resistance values....  even if you remove the pan to do so...

 

Unsure IF this could be speed sensor related, and what the TCU does with that input.

 

another point... the cable adjustment at the throttle body..  IIRC it mostly controls the line pressure,  or am I incorrect on this point... ???

 

 

link to my old post..

 

 

[colthrax]

19 hours ago, llhat said:

 

another point... the cable adjustment at the throttle body..  IIRC it mostly controls the line pressure,  or am I incorrect on this point... ???

 

You are correct, that line only controls the pressure. the toyota version of the AW4 had an electrical thingie instead of a wire that we have.  "kickdown" comes from the TPS sensor

 

I keep my pressure wire thing ziptied to about 70%. But I don't use the TCU for my aw4.

[The86manche]

The more i look through and read on this the more i feel like someone has swapped out the aw4 for a 3 speed and done some messing around.

My two hunched are the Trans is shot, or the Trans isn't compatible with the renix setup.

If the mj has a tcu then it should be an aw4. And my guess is someone didn't know how to work on or fix the Trans so they swapped a 3 speed in that they had. The kick down cable might not be compatible with the throttle body and its just not allowing for proper Trans fluid pressure and shifting.