1997 4.0 Transmission Problems

Hey all!

I recently took over my dad's 1998 Jeep XJ 4.0. This old lady has been in our family for a good 18 years!

We have recently started experiencing some transmissions issues. What would happen is you would put the car in DRIVE and it will essentially slip and not move. It would start to move slightly, but its clearly slipping and not gaining momentum. The same happens when in 3RD. When you put it into 1-2, its fine and pulls as per normal, shiting over to 3RD/DRIVE does still slightly slip, but it generally feels fine then.

What is more interesting is that this is totally erratic. The car would be fine for weeks and then it all of a sudden flares up. This is not related to engine/transmission temps at all as it happens irrespective of driving time, sometimes ice cold and sometimes after driving for hours. The last time this happened I switched off the car, and after starting it again it was fine for about 5 minutes then had issues again.

I did go through the diagnostics and in my mind, it sounds like an electrical issue, most likely shift solenoids. But my mechanic feels differently and thinks its potentially the gearbox clutches that need replacing. To me, if it were the clutches it would be a constant issue. I have not tested the resitance on the solenoids as I am not sure if they would be faulty while the car is driving fine.

Would you agree that this is most likely an elictrical issue, or should I trust my machie?

Thanks!

Does your mechanic have a new boat and the next payment is due ?


Start with the basics, do your own diagnostics. You can find an AW-4 Service and Diagnostics manual with a Google search.

You are using the specified Dexron-III/Mercon and NOT using ATF+4 ? Have you adjusted the Throttle Valve cable on the Throttle body ?

Test the solenoids. Inspect the related wires and wire harness to the PCM for damage and corroded/bent/pushed back wire plug pins. Consider spending a few dollars on a junkyard Transmission Control Unit.

So trying to start in 4th gear with it in (D)? Check that the trans computer has power.

Tim_MN said:

Does your mechanic have a new boat and the next payment is due ?

Click to expand...

Haha, I generally trust my machie, he maintains plenty Jeeps in our area and he is always super reasonable.

That being said, I just don't think I agree with him on this specific issue.

Tim_MN said:

Start with the basics, do your own diagnostics. You can find an AW-4 Service and Diagnostics manual with a Google search.

You are using the specified Dexron-III/Mercon and NOT using ATF+4 ? Have you adjusted the Throttle Valve cable on the Throttle body ?

Test the solenoids. Inspect the related wires and wire harness to the PCM for damage and corroded/bent/pushed back wire plug pins. Consider spending a few dollars on a junkyard Transmission Control Unit.

Click to expand...

I have done a few of the tests listed in that manual. As far as I can tell it is definately electronic. I will test the solenoids and see what they tell me.

Do you perhaps know where the TCU and Fuse is on a RHD model?

lawsoncl said:

So trying to start in 4th gear with it in (D)? Check that the trans computer has power.

Click to expand...

That is interesting, I didn't think of it like that.. :banghead: I just assumed it was slipping in first, but now that you mention it it might as well be in 4th! Maybe some erratic power loss to the TCU...

The shift solenoids are engaged as follows.
1st - Solenoid #1
2nd - Both Solenoids #1 and #2
3rd - Solenoid #2
4th - No solenoids powered

Pulling power to the trans computer gets you 4th gear with the shifter in (D), 1st in (1-2) 3rd in (3), and no torque converter lockup - which could explain why you think it's still slipping in 3rd. Manually shifting this way is actually the first test to help verify whether you have a mechanical problem. Reverse is not electronically controlled and should always work.

If it was consistently trying to start in 4th, I'd really suspect power to the trans computer. Being intermittent, I would suspect a bad #1 solenoid or the wiring to the transmission is damaged. I would not suspect a bad trans computer, as that's a pretty rare failure. A set of solenoids is relatively inexpensive https://www.amazon.com/HERCOO-Transmission-Solenoid-Solenoids-1992-1997/dp/B07F2HM4W4 and can be repalced by removing the pan without removing the transmission. I would certainly check the wiring and measure the resistance of the solenoids first, then try replacing the solenoids before looking at a rebuild.

If you do the solenoids yourself, it's about an hour job. Just be careful that you don't overtighten the oil pan bolts. They only get 5-10 ft-lbs max, which is only moderately snug if doing it by feel. Overtightening will strip the aluminum threads or deform the edge of the pan.

lawsoncl said:

The shift solenoids are engaged as follows.
1st - Solenoid #1
2nd - Both Solenoids #1 and #2
3rd - Solenoid #2
4th - No solenoids powered

Pulling power to the trans computer gets you 4th gear with the shifter in (D), 1st in (1-2) 3rd in (3), and no torque converter lockup - which could explain why you think it's still slipping in 3rd. Manually shifting this way is actually the first test to help verify whether you have a mechanical problem. Reverse is not electronically controlled and should always work.

If it was consistently trying to start in 4th, I'd really suspect power to the trans computer. Being intermittent, I would suspect a bad #1 solenoid or the wiring to the transmission is damaged. I would not suspect a bad trans computer, as that's a pretty rare failure. A set of solenoids is relatively inexpensive https://www.amazon.com/HERCOO-Transmission-Solenoid-Solenoids-1992-1997/dp/B07F2HM4W4 and can be repalced by removing the pan without removing the transmission. I would certainly check the wiring and measure the resistance of the solenoids first, then try replacing the solenoids before looking at a rebuild.

If you do the solenoids yourself, it's about an hour job. Just be careful that you don't overtighten the oil pan bolts. They only get 5-10 ft-lbs max, which is only moderately snug if doing it by feel. Overtightening will strip the aluminum threads or deform the edge of the pan.

Click to expand...

Thanks for all the info, appreciate it!

Yeah, I agree that the intermittent nature of the issue does not point to a total power failure. For example, I went wheeling this weekend and had zero issues the whole day, but driving 5 minutes to the shop the week prior and it did its thing again...

I will test the solenoids and also check for wiring issues. I have seen all these nice kits on Ebay and Amazon, but importing them to SA is a nightmare so will need to try source something locally.

The title says '97, post says 98. Did you change the fluid? Twice? There is a difference between the 97-below and 98-up trans. The 98-up have two speed sensors. I had issues on a '98 slipping. It was the output speed sensor. There are a few electrical items that control the trans. TCU and ECM, solenoids, the speed sensors, the brake light switch, the TPS, and the NSS (Range selector for 98-up). You can clean and repack the grease in the NSS. There are two small springs, that the grease hardens up, that provide tension for the electrical blades. The fun part is getting the NSS off the trans.

The title says '97, post says 98

Click to expand...

Sorry about that, she is a 98 model.

Pulled the pan and measured the solenoids:

• TC lockup: 900ohms
• 1-2 & 3-4: 50ohms
• 2-3: 13ohms

So swopped them out and feels lots better. Looks to be solved :cheers:

Glad to hear.

The trans solenoids can be checked for resistance, along with their wiring, from the engine bay. That way you don't have to remove the trans pan just to test.

For those of us who have never actually measured those solenoids, what would one expect a new/good solenoid to measure for resistance?

Rob Mayercik said:

For those of us who have never actually measured those solenoids, what would one expect a new/good solenoid to measure for resistance?

Click to expand...

Factory specs is 13 ohms +/-3 ohms. As Cruiser stated you can measure from inside the engine bay. It is the black or gray electrical connector up by the trans dipstick. The other goes to the NSS.

cruiser54 said:

Glad to hear.

The trans solenoids can be checked for resistance, along with their wiring, from the engine bay. That way you don't have to remove the trans pan just to test.

Click to expand...

Its worth nothing that I did indeed test these before dropping the pan. Also, disconnecting the plug and driving the car gave me almost exactly the behaviour I was intermittently experiencing which then convinced me to drop the pan.

Thanks for all the help