Torque convereter lock-up

Just bought another XJ, '87 4.0l and it has a few glitches. The worst is that the torque converter is staying locked all the time accompanied by a fairly high rpm (don't know how high cause I have no tach). What controls the torque converter lock-up on these renix models? By the way this is the Cherokee Chief model with a Dana 44 in the rear and the tow package.

How do you know you are in lock up? I was not sure on my 88 XJ until I purchased a snap on MT2500 off of ebay. I drove around and then learned about the operation of my AW4 transmission.

The Tranmission control unit, it is electronic, controls the transmission. It is located just to the right of the ash tray on the back side of that panel.

I noticed my XJ goes into lock up as soon as I shift into 3rd or 4th. I do get unlock when I am going down a hill, etc. With the snap on tool I have been able to associate unlock with a clunk.

I basically can not tell when it goes into lock up but can tell when it comes out. You need someone with the Jeep test set of the snap on to hook it up and you two need to go for a drive and see how your transmission works. Anything beside using the test set is just guessing.

Best guess

I have had some formal training in auto-trannies but every manufacture seems to have something different. When shifting into any gear from neutral at idle, all (or nearly all) electronically controlled transmissions should have the torque converter unlocked. Mine is locked up so that when I'm shifting into gear I get a nice clunk and the XJ wants to spring forward and you have to keep the brake on hard to not go forward.

Since I don't have a tach (I'm working on it) to see exactly when the lock and unlock points are during normal driving, you're right Martin, I'm just making assumptions. I guess my question specifically is what are the commands on this transmission that tell it to lock and unlock? Is it tps, rpm, speed sensor. My manual doesn't cover this.

This leads into some problems with the torque converter problem I had with my van. The door warning sensor was in the same circuit as the ECU. When one of the door switches was shorting it screwed up my ECU and would put my transmission control into safe mode which locked up the converter. It took 6 months of taking it to the shop that had rebuilt it for them to find a tsb that told what to do for this problem. Switch changed, no more short, transmission runs fine.

I don't think you are getting lockup, or when you shift into gear the engine would stall. Sounds more like you have a high idle speed problem, which may be associated with the TPS or the IAC (Idle Air Controller).

Step 1 would be a good cleaning of the throttle body and associated sensors, followed by adjusting the sensors. I believe procedures have been written up on this forum if you don't have the Renix MPFI FSM.

Thanks

Thanks guys. First things first. I guess I should do a thorough clean and adjust. By the way Eagle, the engine doesn't stall, almost but not completely. I have to pop it out of gear at a stop light or I'm down to what seems like 400-500 rpm. At any rate I'll do all of the adjustments and take it from there.

Re: Thanks

HossHoffer said:

Thanks guys. First things first. I guess I should do a thorough clean and adjust. By the way Eagle, the engine doesn't stall, almost but not completely. I have to pop it out of gear at a stop light or I'm down to what seems like 400-500 rpm. At any rate I'll do all of the adjustments and take it from there.

Click to expand...

Someone will surely correct me if I'm wrong, but if the converter were actually staying locked, it wouldn't just bog down, but stop dead. You'd have to be burning up the TC lockup clutch to stop it at all. If the idle speed is higher than the stall speed of the converter, though, I would expect it to bog down lower than if the idle were correct. So I'm with Eagle on this.

If you are really convinced that the TC clutch is staying engaged, you could temporarily disable the TCU (pull its fuse or its plug) and manually shift through the gears, and see how it behaves.

There is also a write-up on controlling the lockup with a toggle switch. I have no need for it so don't have it bookmarked, but I'm sure a search will turn it up. It's basically just putting a toggle switch in the circuit that tells the converter to lock.

there are several sensors that feed into the TCU, then just 3 lines that run from TCU to tranny. The first two control gear selection through different on-off combinations and the third locks the torque convertor when power is applied. Unplug your TCU and the tranny should not lock the TC and it will shift 1,3,4 (no 2nd)

you can find the AW4 manual here: http://www.pirate4x4.com/tech/billavista/PDFs/AW4_manual.PDF

I don't know if this helps ... on my '91 ... the brake pedal switch sends an electronic signal deactivating the lock function on the converter.

To check and see if the converter is locking-unlocking ... drive at highway speed in 3rd or 4th ... slightly depress the brake pedal while on constant throttle ... if the RPM jumps it's an indication it unlocked ... lift the pedal and it should lock and reduce the RPM.

Simple but effective.

Thanks

I've found some problems with the sensors on the engine and with the vacuum. I don't believe now that the torque converter is locking up but have come up with transfer case problems. I'll make a new post after I do some more troubleshoooting. Thanks for all the input! More to come as this is my first aw4.

FWIW

When I fixed up the "Montana-mobile" (an '88 Laredo) and drove it across the country, I was surprised at how quickly the torque converter locks up. Seemed to lock almost instantly after the tranny hit fourth gear, and made it feel like the engine was lugging unless I really had my foot in it.

A local friend who used to have a '94 recently bought an '87 XJ Wagoneer, and he commented on the same thing -- torque converter locks at what seems to be a lower speed/RPM than you would normally expect. This seems to be characteristic of the way AMC had those trannies set up.