2001 XJ8-L (x308, 4.0L, zf5hp24). 118k miles.

When cold, say in the morning, after being parked overnight, car runs and drives fine. It has never misbehaved on my ~15 mi morning drive to work.

When it gets warm, it sometimes experiences severe power loss and shifting issues. Difficult to even limp it to safety when this happens. Sport mode, or manual shifting do not seem to help.

A-drum, A-drum clutch pack, and pressure control valve have all been recently replaced with upgraded components. A-drum had suffered the usual snap-ring failure. Trans fluid level has been checked and re-checked.

No check engine light, or other indicators to help guide us.

Seems odd that letting it fully cool down restores proper function.

Ideas? Has anybody figured out how to put a transmission into these cars that is a little less terrible?
Thanks ;-)

 

Hi Ryan,

Until one of our X308 experts responds, I'll throw out a few questions and ideas:

First of all, you mention that the CEL is not illuminated, but have you had the car scanned for any stored fault codes?

How long since the last tuneup (fuel & air filters, plugs, cleaned the MAFS, etc.)?

Any indication of problems with the catalitic converters?

Is there any indication that the engine is overheating?

The fact that your symptoms occur only when the engine is warm could suggest a problem with one or more sensors the ECM relies on for determining the air-fuel ratio (AFR) and/or ignition timing.

For example, if the Engine Coolant Temperature Sensor (ECTS) does not tell the ECM that the engine has warmed up, the ECM may continue to apply start-up fueling enrichment, leading to a rich AFR. Monitoring your fuel trims and other live data might give you a clue.

Other sensors that could have a temperature-sensitivity include the O2 sensors, the Intake Air Temperature sensor (IAT), MAFS, CPS, etc.

Could a problem with the Variable Valve Timing (VVT) system cause your symptoms?

Could a critical relay be malfunctioning when hot? The ignition positive relay, throttle motor power relay, fuel injector relay, ignition coil relay, and engine management system relay are all in the engine compartment. It might be worth swapping an unimportant relay for the critical relays one at a time to see if things improve.

It might be worth checking for corrosion in the relay sockets and on the ground points used by the EMS, and on the electrical connector for the ECM.

You can download the 2001 XJ Electrical Guide here:

http://www.jagrepair.com/images/Auto.../jagxj2001.pdf

Cheers,

Don

 

Thanks for all the input and ideas Don. Going down your list:

I haven't scanned the car for a while. Last time I scanned it, no codes (active, pending, or stored), but it is time to check again. I do have access to a scanner that can go look at the various systems, including the transmission.

Tune-up was done recently.

Problems come on pretty suddenly, and when it is behaving well (90% of the time) it is a strong runner. I don't think it's catalytic converters.

No engine over-heat.

The range rover guys share these transmissions, and I've found some good info on their forums. The O-ring failure described in this post:
ZF 5HP24 teardown
might be my exact problem. We did the A-drum repair on the transmission, but didn't dig into it any deeper than that. If I've got a weak or failed seal in the trans, then that could explain why/how my problems are related to transmission temp (ATF viscosity).

After the A-drum rebuild, we filled it with Amsoil ATF, which claims to be compatible with the 71141 spec. I am wondering if going to the regular ESSO fluid might improve things. The consensus seems to be that the Amsoil fluid should be fine, but I wonder if the ESSO fluid might have more stable properties with temperature variation. Unfortunately, this would be an awfully expensive little experiment to try.

 

Following the KISS principle, since the problem is temperature related, I would clean or replace the temperature sensor coming from the crossover pipe. Don's description sounds like what you are seeing. Then, maybe the Thermostat (are you overheating?).

 

Ryan Border - describe the shifting problems that you encounter. Also, have you had this problem since the transmission was repaired?


Your 15 mile drive to work is more than enough to bring the engine to operating temperature but the problem doesn't occur. This may indicate that it is not the engine temp that is causing the issue

 

I don't think it's engine temp related. As you note, 15mi is plenty to bring the engine up to temp, and I don't correlate the problems with higher or lower engine temps, or engine load.

My guess is that it is transmission temp related. Unlike the engine temp, controlled by the thermostat, the transmission temp is slower to rise. The more I drive the car during the day (and maybe the hotter the weather, hard to be sure yet), the more likely the car is to have troubles. I am thinking that the transmission is very slow to bleed heat off, and over the course of a day, heat builds up in it.

Let's see if I can describe the problems better. The problems seems to start out with a minor shift hesitation at speed (maybe at 50mph or so). As it gets worse, the shifting problems become more severe- as if the car is searching for a gear. At that point, it seems to me, something is cutting power to the engine. My *guess* being - the transmission is telling the ECU it is trying to shift, and to cut power for a moment... but that moment drags on much longer than it should. When things get bad, I am only able to drive the car with a feather touch on the throttle pedal. Anything more than that, and it cuts power to a minimum. Climbing a hill (like the one up to my house), max speed might be 20mph... I'll need to pull over and let traffic by. On level ground, by feathering the throttle, I can eventually get the car up to cruising speed (60+ mph), but it takes a while. One time, when it was acting up, I decided to see what would happen if I floored it... there was a big/thud bang from the trans... I won't do that again.

More info: after the A-drum fixes the car seemed to be driving fine. The trans did sometimes make kind of a whining noise. The first time I saw the problem was after a long mountain descent (~2500 steep vertical ft), where I used engine braking (manual transmission gear selecton) to control the speed of the car, on a hot day. Since then, whenever the car is used extensively, it seems to have troubles by the end of the day... I attribute that to heat build up in the trans, but that is just a guess.

I've wondered if I should maybe try to flush the transmission cooler-

Of course, the problem first showed up, literally 2 days after I decided things were fixed, this car was going to be a keeper for a while, and I sold the car it replaced :-)

 

Do you think the problems are from the trans overheating or are they happening even though the trans is not above normal operating temp? Can you check the temps of the trans cooler lines to see if the temp differential meets specs?

 

What is "normal" transmission operating temp? After a ~15mi drive this morning, the bottom of the trans pan was hot to the touch. Not hot enough that you couldn't touch it, but definitely very warm- uncomfortable to touch for a long time.

Since the transmission is "cooled" with a water-to-oil cooler (on the radiator), it seems like the minimum trans temp - when things have stabilized - would be the engine coolant temperature (since that is what's cooling it).

Tried scanning it today - the Pegisys scanner I had was having troubles talking to the TCM. Might be another clue. Will try other scanners later this week.

 

What is the tachometer doing during all of this.

If the car is not moving because the engine is not giving power that is one problem (engine) -- if the engine gives power and the trans is slipping that another (trans).

The tachometer will tell you.

If the engine is not giving power -- most of the problems will cause a fault to show up -- like the common TPS sensor .. except the fuel pump. Your pump maybe overheating/ failing and causing the engine to be starved for fuel.

The XJR has two pumps -- it is my understanding that the non SC cars only have one. All mine have been R's.

 

I do not think this is a typical transmission (internal clutch) slipping issue. I don't see the motor rev, like you would with a slipping clutch or torque converter. Fuel pump is new - and it really doesn't seem like a fuel starvation issue.

When it first started, I wondered if I had a loss of (engine) power, which was causing the transmission to misbehave... or, did I have a transmission issue which was resulting in the car cutting power to the motor. It's hard to describe exactly how or why... but I am pretty convinced this is a transmission issue first. It first starts out with rough/delayed shifts, with no change to engine behavior. It's only when the problem progresses to the later, more severe stages, that the motor power is reduced.

Today, I put about a bottle and a half of Lucas transmission treatment into it. Just opened the fill plug, let it drain/cool (lost about 1.5qts) and then re-filled, using the regular procedure, with Lucas. Could be the old placebo effect... but it did seem to change the shift characteristics (under normal conditions), and the car did not act up on the exact drive where it has been giving me the most troubles lately (I recognize that it had about 1.5 quarts of "cold" fluid injected too). Will be interesting to see if it continues to do better. If a tweak to the fluid properties ends up making a significant difference for this problem, that will tell me something. I figured there was a 1/3 chance that trying this would actually make it worse; 1/3 it would help, and 1/3 that I was on the wrong track and there would be no change at all. But, it was a much cheaper experiment than a wholesale change from Amsoil back to Esso or Mobil1.

My understanding is that the root cause of the A-drum failure is a failing pressure control valve. The failing valve, allows high pressure spikes through, which put a shock load into the A-drum (on the snap ring) eventually breaking it. So, part of the repair/retrofit (the one I just completed) is an "upgrade" to that pressure control valve. I'm sort of scratching my head, wondering if my new pressure control/reducing valve has maybe working just a little "too" well, reducing pressures in the trans just a little too much when the fluid is up to temp and operating with reduced viscosity.

 

Ryan,

I just pulled these links together for another member and thought I might as well post them here too in case any of them may be helpful to your situation:

You can download the 1998 XJ Electrical Guide here:
http://www.jagrepair.com/images/Auto.../jagxj1998.pdf

The 1998 Transmission Diagnostic Trouble Code Summaries is here:
http://www.jagrepair.com/images/Auto...tem%201998.pdf

This Technical Introduction provides some clues as to how the ECM, TCM and ABS interact:
http://www.jagrepair.com/images/Auto...ansmission.pdf

This document explains the transmission control system:
http://www.thejagwrangler.com/upload...on_control.pdf

Cheers,

Don

 

Thank you very much for those links Don!

 

With all of the engine/ transmission management controls I have to believe you would get codes and restricted performance warnings if one was telling the other to cut power. Is you dash working correctly? JUSt wondering if you are getting a warning and not seeing it.

When this occurs -- does the car coast freely. The engine is too powerful when working correctly to be held back -- think holding the brakes and hitting the gas.

I would also bet that the transmission temp is monitored -- so that a possibility -- that should also set a code.

 

I think you need to get an OBD reader installed while the car is running. Like to hear about what codes are showing and what is the real temperature when the fault occurs.

 

It has been a few months, and I just figured I'd give you guys an update.

The weather got cooler here, which has made the car happier. I also swapped out anther quart of trans fluid for Lucas, which seemed to improve it again. I've been driving the car almost daily, and the problems are pretty much gone.

I have had the car act up a couple of times - and have correlated it to the fuel level. I do think it is temperature related; but I am now suspecting that at least some of the problems might be due to the temperature of the fuel pump. When the tank gets low, the body of the pump is no longer cooled by the fuel. Both times, when it's acted up, I've stopped, filled the tank, and the problems immediately went away.

Still shifts a little slowly (seems to hang up mid-shift) sometimes, but over-all, the car is actually driving very well. I'm not motivated to pull the fuel pump out again; at least until or if hot weather makes it more of a problem next summer :-)