@Don B : Thanks for your tool recommendations, I am trying to find something similar in Germany. I think might do, though I am surprised how expensive just a few cables can be. https://www.conrad.de/de/p/vigor-v4326n-messleitungs-set-1-set-2866075.html?hk=SEM&WT.mc_id=google_pla&gad_source=1&gclid=Cj0KCQjws560BhCuARIsAHMqE0GkbE-HsgZigj3sCWVkZDENSQEkYS5nvKTTTRRvfvjDGErRMHPoTqYaAitxEALw_wcB are even more expensive but also more extensive. And https://werkzeugstore24.de/bgs-krokodilklemmen-kabelbox-selbstaufrollend-15-m-9401.html?gad_source=1&gclid=Cj0KCQjws560BhCuARIsAHMqE0H9W96cXp-6tpf8brp103Tvz2J1VhcYBJemhzGdYknEma1ZdFA7gYQaApOhEALw_wcB.

@newyankee
I watched some videos of 4L80E (valve body) overhauls und reinstallations, the TCC solenoid should come out without removing the valve body (jal1234 also confirmed it), but the valve itself probably not, there is too little space and it seems like it needs unlocking from inside. Actually I am not 100% sure whether the TCC is working or not, but I guess the rev leaps in certain situations definitely point towards it.

@Gijzzy I tried, but I didn't manage to flash out any code, not sure if that means something is wrong with my TCU or whether I just lacked the right tools .. I hope the latter is the case.

 

Just to cry wolf: what if the tranny had to come out completely (e.g. for converter replacement), how could that be accomplished? I doubt the upper mounting bolts can be reached from the engine compartment from top, would the whole front axle + engine+ tranny have to come out? Or would it be sufficient to lower the rear engine mount to access all the mounting bolts? The official workshop manual has a gearbox chapter that roughly describes how the transmission is designed and integrated to the car, but there is no mention on neither how it should be serviced nor how it could be repaired or replaced.

 

Using an engine bay cross bar to support the rear of the engine, unbolt the trans mount and lower back of trans. Use very long extensions to remove bolts while supporting the trans with a trans jack. You probably will need to remove engine driven fan so that it doesn't hit the fan shroud when the back of the engine is lowered. Of course you'll likely need to remove exhaust portions to gain clearance and remove the torque convertor to flex plate bolts, etc.

Jon

 

That doesn't sound too bad. But first let's see what I can about it leaving the gearbox in place. Before it reaches temperature everything seems to work well, so according to what I have read it could fairly be something related to either wiring harness, oil pressure or a hampered TCC solenoid or valve regulator. A new internal wiring harness + TCC solenoid wouldn't cost too much and would be fairly feasible (not considering the exhaust), but when I disconnect the old harness it could very likely happen that the connectors on all solenoids break due to brittleness. So indeed it would probably be a good idea to have a complete set of solenoids at hand once you look behind that door.

I had another look at the oil pan situation and I am not quite convinced one exhaust pipe has to come out in order to take the pan off. There is a little space towards both sides, if you manage to loosen all the bolts, one could possibly fiddle the pan out between the exhaust pipes.

 

I did probe a little more today, I am able to get to all the oil pan bolts and once it is loose, I should be able to drop it a few cm and slide it to the front towards the engine oil pan. Then I think I should be able to twist and tilt it and finally slide it out. If necessary I could remove the fly wheel cover, it's just a few bolts. And if that doesn't help it, I could even undo the engine oil pan, that should finally give enough clearance. I think I'd rather do a engine oil change and pan gasket than ruining the exhaust. The only issue I see: someone fastened the pan bolts to excess, I tried to undo one with a cranked wrench, but it didn't move. That might become a littly tricky, because there are some bolts than I cannot reach with my power wrench.

I also did some more test driving, I think the TCC works, even when the gearbox is at temperature and the TWL has come on once (just needs a restart). But I only notice it when coasting down, so when it is disengaging. Don't notice it engaging, but it has to otherwise it could not disengage. The TC shudder I sometimes notice could be also related to topography, coasting down downhill seems to facilitate it.

 

Man that sucks, the bolts sit so tight, can't get them loose with a hand wrench. Even my 80NM powerwrench couldn't break them loose, needed a huge ratched with telescope prolongation and surely 100-120NM to loosen one of the easily accessible ones. So it looks like I do have to cutoff the exhausts to get all of them. What would you recommend, cut them at the weldseams or somewhere inbetween?

BTW: Observed the TCC disengage today while coasting down and TWL being on! That actually contradicts what the GM manual says, with error code 68 it should inhibit TCC operation ... as well as manual shifting. So maybe I have another error code? Or maybe even multiple, interchanging error codes? In that case a proper diagnosis would be great, but once again I am turning cycles.

BTW2: It looks like the connector of the inner wiring harnes is held to the gearbox housing by a hexagonal ring. That 's barely accessible with the rear transmission mount being in place. I watched some videos of 4L80E overhauls, they always just tapped the connector with a hammer and pulled it through, but these transmissions were all removed from the car.

Where to cut

Connector

 

The videos you watched where they removed the connector by tapping it out had the standard GM wiring harness, not the Jaguar/Rolls Royce connector. Completely different.

Jon

 

I though something like that. How did you manage to change it?

BTW: Do you see that insulation mat? It's hanging all over the transmission, I doubt that that is the way it is intended to be. Shouldn't it be attached to the propeller shaft tunnel or does it belong there at all?

 

I didn't change the harness, as it took too long to come. I'll likely change it the next time I do fluid and filter.

As far as the mat goes, I'm not sure. The TH400 cars had a foam sound deadener wedged beteen the trans and tunnel. It wasn't glued in place. I don't recall what was there on my 95 V12.

Jon

 

I just looked at my new harness. The connector is held in by a large nut on the outside. You'll need a 32mm socket to remove it.

Jon

 

That's interesting ... then it seems to be the same on the XJ81, that foam mat looks like it is just wedged inbetween the trans and tunnel.

That's gonna be tricky, with the exhaust pipe (and the foam mats) in the way, it will be difficult to reach the connector nut by either a socket or wrench ... maybe with a prolongation from behind the trans mount.

Before cutting the exhaust I wanna give it another try, ordered me some special 10mm cranked wrench that would allow me to put a straight prolongation on the opposite end. Maybe I can get the pan bolts off this way.

 

I did some more test-driving and I am starting to doubt it has anything to do with the TC or TCC, because as long as I avoid accelerating in 4th gear at a certain throttle angle, there will be no fault and it looks like the TCC is operating as designed, even when the gearbox is at temperature. It still could be anything like a bad wiring harness, or solenoid or whatever, but now I am rather thinking about a speed sensor. The engine speed signal seems to come from the ECM (respectively the crankshaft position sensor), does anyone know where I could probe that? Would the engine fire up at all with a bad crankshaft position sensor?

Another reason why I cannot nail the cause down might be that the documentation I have does not fit the model year of my XJ81, it's from 1995 so that is actually X305/ late XJS era. Maybe that would also explain why I cannot flash out hte error code, I might be referring to the wrong pins.

Besides that I am starting to notice a slight pulsation in the driveline when going at a steady speed since I have added some more ATF. It feels like the overrun clutch is slighty engaging and than disengaging again. Don't know if that means anything.

 

The output from the engine ignition module could be probed either there or at the TCU. The transmission also has its own speed sensors, one on the input, and one on the output. Yes, the engine needs the speed sensor to operate to run.

 

Now that I have fixed the fire damage I can once again come back to my gearbox issue. Cause of this occasion I got me some better electric equipment, so today I started another approach to flash out the error code. But no chance, grounding pin A8 doesn't cause any flashing. But at least I am now measuring 2,6mA, so there is electricity and my equipment is working. I tried some of the other free pins hoping that they had different usage on 1993 cars, but nothing happened. I also mistakenly grounded A4 (which I later found actually not being free) and it caused the engine to stop immediately giving me a check engine light.

I could continue grounding all the other free pins until some TWL flashing happens, but I am afraid I could possibly toast one of my control modules or whatever else.

Besides that I made an interesting observation during today's testdrive: I was coasting downhill at constantly 78kph which is pretty much exactly the speed where the TCC normally disengages when coasting. But it was continously engaging and disengaging for at least 10 times - until I finally accelerated above 80kph.
So I am wondering what happened there: was this a TCC (... solenoid or valve) failure or was the TCM rather getting a false speed signal, causing itself to send alternating TCC engage/disengage commands?

But I have to tell that I have already noticed this kind of TCC disengagement 'shudder' even without the TWL being on or being engaged. So this behaviour seems not to be (directly) related to the TWL issue. The last few times the TWL came on it was at speeds above 100kph. But maybe that still all points towards a speed sensor issue.

My idea was to simply switch the input and the output sensor which would hopefully result in in different TWL behaviour but the sensors are so hard to get by with the exhaust pipe being in place. I managed to losen the input speed sensor but I wasn't able to pull it out, it seems to be stuck ... for reaching the output speed sensor I have to lower the gearbox and remove the exhaust pipe.

 

Hurray, I finally managed to flash out the error codes!!!

I figured out I had grounded the wrong socket the last time, it was refering to as C8 ... not A8. Today I grounded A8 and it finally flashed out codes.

The first time I got 2 codes, 68 and 71. Then I erased the codes and drove again until the TWL came on again. Then I read again the codes and this time I only got code 68 (71 was maybe caused by grounding the pin that stopped the engine (which btw had fuel fail 77 since then)).

68 is 'Overdrive ratio incorrect' and could be related to either input speed sensor or engine speed signal. The latter would go hand in hand with 71 ... since the engine works fine I think it could be only a bad connection between TCM and ECM. Or if it is the input speed sensor a bad connection to the sensor or a bad sensor.

That gives me a good direction, just need to figure out where the engine speed signal comes out of the ECM and where it goes into the TCM. The input speed sensor is as I found out a little difficult to reach ... but maybe I can at least measure the connector before messing with the exhaust pipes.

 

I found this on another forum for error code 68:
"This is as common a problem in a 4L80-E. Torque converter clutch solenoid valve and bore wear. If you change your fluid frequent enough you might forestall the problem.
Actuator feed limit valve can play into it a bit. My blame lies in the TSS solenoid signaling system. That and within the pump. There are two valves that need to be wet air tested within the pump. (WAT)
TCC solenoid as well. (WAT) This verifies hydraulic issues you notice as OD going out when the fluid gets hot.

Simple fix if you go to the right shop Who knows.
Shops who don't will answer enough questions to satify the average customer and you get a rebuilt transmission without the stated above.
Its not all electronic.
It can be hydraulic (like in this case).

Computer is doing its job just fine.
solenoids are doing their jobs as well."

How old is the tranny fluid? It thins with age. Try a bottle or two of Lucas Transmission additive. It can help with fluid pressure issues like this. I've used it in Mercedes with success.
Jon

 

You just smashed my hopes it could be as easily fixed as replacing the input speed sensor.

But there is indeed a weak point in that argument: why does it only happen, when the transmission is at temperature, not when it is cold? And it is possibly related to the amount of ATF in the gearbox (which will also relate to pressure somehow). The only explanation I could think of is that the TCM does not monitor this condition until it is at temperature. But I guess that is rather unlikely.

I think I had the ATF replaced about 5 or 6 years ago, that's maybe 15K km. But I assume the fault exists much longer, I'm not sure if I mentioned it already but: I bought the car without TWL (=no bulb). And I never noticed that because most of the time the TWL is covered by the steering wheel, so it took another experienced Jag owner to recognize there is a bulb missing in the dash. And that's when I got started.

Actually I talked to several shops that do transmission overhauls, at least one of them familiar with GM products. He was mentioning some strange kind of defect, related to pressure and the oil pump ... but anyway he recommended me a complete overhaul.

But however, I would like to sort out that speed sensor before taking any other measure ... do you know the pin assignment on the TCM and ECM? I could not find it in the workshop manuals I have and what I found on the net does not correspond to the sockets I have on my control modules.

And I do have a spare speed sensor here - I could replace it with the input speed sensor, just to see if it makes a difference. I just need to find a way to get the old one out.

 

As the transmission and its oil warms up, the oil gets thinner. As a result, system pressures can be lower than when cold. That's why I suggested the Lucas product. It essentially thickens the oil some, causing somewhat higher system pressure.
i don't have anything specific on the XJ40. I'd check the XJS electrical diagrams for your year. The TCM should be the same, don't know about the ECM, but I expect it's the same. The XJS diagram books are here:
JagRepair.com - Jaguar Repair Information Resource
Jon

 

This is the Lucas product I discuss above.
http://Lucas Oil 10009 Transmission ...a.co/d/fPkXziW

 

That link doesn't work but I guess you mean this: Lucas Transmission Fix?