Converter Lockup Problems

Hello,

I just purchased my 1st XJ... A 1997 sport 4.0. I am having troubles with the lockup converter.

The transmission shifts fine through all gears but the converter will switch between locked and not locked at random times while on the highway.

Some times the thing works fine.

Some times at highway speed it will switch between locked and unlocked about once a second for miles.

Other times, it will run unlocked for about minute, then try to lock and instantly jump back to unlocked... over and over again.

I am planning on changing the fluid and filter this weekend and am wondering if there is anything else I should look at replacing or looking at while I have the pan off...

Are there any solenoids or sensors I should look at replacing at this time?

Thanks!

I would start at the simplest which is check all of the electrical connections including grounds for the solenoids involved in the TC lockup. Sounds like you might just have an intermittent connection. Other than that some debugging could be done by checking voltages etc.

Some related info here:

http://www.naxja.org/forum/showthread.php?t=959826

Can also be caused by electrical noise or interference from the alternator, check that wiring as well.

Look for XJ service manuals online in PDF format, they're out there.

When you say "lockup" do you mean the jeep jerks and bucks at highway speeds? Do you happen to get any CEL when this happens?

If you have cruise control, there is a switch high up on the brake pedal arm that has two functions. One is to release the vacuum and thus turn off the cruise function, the other is to tell the torque converter to unlock when the cruise is turned off. This switch can back away from the brake pedal arm and cause the problems you describe. Fix is to adjust the switch closer to the brake pedal arm so that it is fully actuated....its a pain to get to and adjust....

tugalo said:

If you have cruise control, there is a switch high up on the brake pedal arm that has two functions. One is to release the vacuum and thus turn off the cruise function, the other is to tell the torque converter to unlock when the cruise is turned off. This switch can back away from the brake pedal arm and cause the problems you describe. Fix is to adjust the switch closer to the brake pedal arm so that it is fully actuated....its a pain to get to and adjust....

Click to expand...

The brake light switch has 2 sets of wires, one goes the TCU computer to disengage the TC when brakes are applied.

tugalo said:

If you have cruise control, there is a switch high up on the brake pedal arm that has two functions. One is to release the vacuum and thus turn off the cruise function, the other is to tell the torque converter to unlock when the cruise is turned off. This switch can back away from the brake pedal arm and cause the problems you describe. Fix is to adjust the switch closer to the brake pedal arm so that it is fully actuated....its a pain to get to and adjust....

Click to expand...

The Renix setup was this way. I don't believe a 97 has the seperate switch, but rather another wire coming off the single switch as Eco mike said. But yes, if that switch is goofy it can cause unusually t/c unlocking.

To answer some of the questions...

When I say "lockup" I mean the converter is jumping out of locked and unlocked at highway speeds. It doesn't buck or anything... the thing just jumps up and down a few hundred RPMs as the converter does its dance...

My cruise isn't working either and my airbag light is pops on and off but I am assuming this is a clockspring connection problem...

As far as a check engine light... no... I haven't checked the codes yet but I am planning on doing a little troubleshooting this weekend.

I just wanted to see if there was a common problem that I wasnt aware of before I tear it apart this weekend. I am going to grab a service manual and go to town after work..

Thanks for the help...

One last question... would a year 2000 service manual be similiar to a 97 in this instance? I'm not sure what changes they made over the 3 years.

Thanks!

KTOKTO said:

To answer some of the questions...

When I say "lockup" I mean the converter is jumping out of locked and unlocked at highway speeds. It doesn't buck or anything... the thing just jumps up and down a few hundred RPMs as the converter does its dance...

My cruise isn't working either and my airbag light is pops on and off but I am assuming this is a clockspring connection problem...

As far as a check engine light... no... I haven't checked the codes yet but I am planning on doing a little troubleshooting this weekend.

I just wanted to see if there was a common problem that I wasnt aware of before I tear it apart this weekend. I am going to grab a service manual and go to town after work..

Thanks for the help...

Click to expand...

OK... That's what I was wondering because the problem I had in my 97 at highway speeds was a bucking problem caused by electrical short. I had no RPM variations either... Sounds like you have a pretty good idea what direction to go with the troubleshooting... Good luck with it!

You are correct, my reply was for for a Renix set-up. On a renix, the brake light switch is only for brake lights. Easy way to check if the vacuum side of the cruise control is working is to remove the larger of the two lines that go to the cruise servo and plug the outlet on the servo. Then drive it and engage cruise, if it works, then the cruise problem is a vacuum problem. be careful tho...the only way to shut down the cruise when doing this is to turn off the switch on the stalk.

tugalo said:

You are correct, my reply was for for a Renix set-up. On a renix, the brake light switch is only for brake lights. Easy way to check if the vacuum side of the cruise control is working is to remove the larger of the two lines that go to the cruise servo and plug the outlet on the servo. Then drive it and engage cruise, if it works, then the cruise problem is a vacuum problem. be careful tho...the only way to shut down the cruise when doing this is to turn off the switch on the stalk.

Click to expand...

I disagree, my Renix has a dual electric brake switch, and IIRC the second electrical connection on the brake light switch goes to the TCU. IT also has an upper white switch which I think is a vacuum bleed and electric switch combo for the Cruise control.