TCC solenoid lockup problem? Or something else?

I have a stock 93 XJ 4.0 litre auto, owned since new. It has done 120k miles, mostly highways and desert-roads, and been well-maintained.

I've just recently noticed signs of a problem, and I'm not sure what to check on the vehicle, or where to look on the forum for advice. I've browsed posts on the TCC lockup, but I'm still not quite sure if that's where the problem lies.

Symptoms are that when driving above about 40-45, and cruising on light throttle or accelerating gently, if I lift off the gas I get what I'd call "driveline shunt": a slight but noticeable hesitation (rather than the normal freewheeling/gradual slowing as the revs drop) and a seat-of-the-pants feeling which is a bit like a hard downshift. It feels as if either the propshaft or rear diff 'clunks' as the engine torque drops. It's not a clunk loud enough to hear, though.

Doesn't always happen (and intermittent problems are the worst to identify!). And there's no problem below 40mph, where lifting off results in the revs dropping and normal silk-smooth downshifts as the Jeep slows down towards a stop.

I haven't recently made a long-distance run to see whether lifting off at rather higher speeds still produces this hesitation and slight 'clunk'. But I can't say I've noticed the problem when the engine/transmission is warmed-up or hot.

I've heard that the XJ rear diff and driveshafts are known to wear or get slack with age. But I assume that if this were the problem, I would feel that slackness, and maybe hear a mechanical noise, on every shift - or on both hard acceleration/downshift and sudden deceleration.

I also wondered if it was some sort of fuel starvation issue, though this seems unlikely.

I'm suspecting it may be something to do with the TCC lockup solenoid. I had a problem on another car with a GM 3speed auto where the lockup would not disengage because the solenoid had failed (easy to diagnose because the car stalled at the lights!). How does the Jeep lockup work, and does this rather faint set of symptoms on my Jeep point to some sort of misbehaviour by the TCC lockup solenoid? If so, what further tests can I do to narrow down the precise problem - and of course thereafter, what's the solution?

br1anstorm

Hard to tell anything from your description yet, but the TPS (Throttle Position Sensor) is a wear item, and they get worn noisy spots that do weird stuff as the throttle crosses that noisy spot. The TPS is carbon brush variable resistor, and they do were out. This may be early signs on yours.

You can test the TPS with and ohm meter for bad spots using an old style analog ohm meter.

Thanks Ecomike...

I put all the clues/symptoms I could identify into my initial post - like I said, it's the intermittent or transient problems that are hardest to diagnose.

I still worry about the solenoid, not least because I know the lockup is set at around 42-45 mph, and it's above that speed - or lifting off at around there - which produces the weirdness. Could the lockup be "sticking", or switching on/off/on instead of disengaging cleanly when I lift off the gas?

If the TPS is on the way out, I have an old-style analog ohmmeter, but no idea of how/where to test the TPS. I have the Haynes manual somewhere ( I wonder if that explains...) . Otherwise, any tips on the what/where and how of testing with a meter would be appreciated!

br1anstorm said:

Thanks Ecomike...

I put all the clues/symptoms I could identify into my initial post - like I said, it's the intermittent or transient problems that are hardest to diagnose.

I still worry about the solenoid, not least because I know the lockup is set at around 42-45 mph, and it's above that speed - or lifting off at around there - which produces the weirdness. Could the lockup be "sticking", or switching on/off/on instead of disengaging cleanly when I lift off the gas?

If the TPS is on the way out, I have an old-style analog ohmmeter, but no idea of how/where to test the TPS. I have the Haynes manual somewhere ( I wonder if that explains...) . Otherwise, any tips on the what/where and how of testing with a meter would be appreciated!

Click to expand...

Test the ground and output (return wire) with power off. The third wire is the 5 volt input from the ECU/PCM so find it and test the other 2 wires, one of which is ground. Test with power off on Ohms scale. Once the meter contacts are made, then slowly move the TPS throttle from idle to wide open throttle looking for smooth slow changes in ohms reading. Repeat the test several times. If you find a noisy (needle jumps up and down) spot that is your problem.

Also might change the fluid a few times to see if the wrong fluid was put in there. Lost of write ups here about people using the wrong tranny fluid. Use only Dexron III!!!!!!

Has the fluid ever been changed????

There are write ups here and links to picture write ups here on the TPS and testing if you need more details on it.

Haven't yet tried testing the TPS - I'm waiting for the weekend and better weather (it's sub-zero and snowing at the moment). But daily-driving this week reinforces the feeling that it's more like a transmission problem, not a fuel-related one.

Only happens above 40-45 mph. No uneven running at any revs in any lower gear when accelerating or decelerating below that speed threshold. But when above 40 or so, and with light load (ie accelerating or going up a slight incline), if I lift off sharply there's a very definite 'clunk' which feels as if it's coming from the driveline (propshaft or rear diff). If I lift off when cruising on level ground or coasting lightly downhill, no clunk, vehicle slows down gradually as usual.

This makes me think the 'clunk' occurs when there's a marked torque-shift (or torque reversal) between tranny and driven axle. If so, does this point to something slack or worn in the driveline? Or is the auto trans lockup - if it is in fact engaged as early as 40mph - "banging" out of engagement more abruptly than it should, when I lift off and the power drops?

Oh by the way, auto fluid was changed - at around 60k miles, which was a while ago - and as far as I recall it was definitely refilled with Dexron III.

I do plan to test the TPS. But I have a gut feeling that it isn't the problem. Anyone care to comment on these latest thoughts?

br1anstorm

That last description sounds like a u-joint on the drive shaft going bad.

When you can get under it, grab and turn the drive shaft CW and CCW back and forth, and up and down, pull and tug to see if there is any play in one of the U-joints.