Yes, that's it.
Jon

 

After having worked through the wiring diagrams I did some metering today.

As first approach I measured resistance of the engine speed signal between the ECM and the TCM. The pin setup of the ECM was quite clear (even though being mounted upside down compared to the scheme from the workshop manual) but the TCM connectors are not labelled unambiguously, so I tried several pins that could possibly be the correct counterpart - and I measured resistance (~30KOhm) on almost every pin. I could hardly believe that, so tried another signal, the ignition retard request. This time I still could measure resistanc on several pins but not on almost all. And there was pin that had a significantly lower resistance (several Ohm, not KOhm).

But that would still mean that there is a lot of interference and probably damaged isolation. Actually the ECM connector cables look a rather wild to me - is that OEM style? After having measured the transmission speed sensors I gave the ECM another try but could not measure resistance at all - strange.

The transmission speed sensors turned out to be good, measured between 0 and 0,6 Ohm.

 

Connectors were disconnected at each box?

 

Yes!

 

Then what you are seeing doesn't make much sense. I don't see how things would work at all with what you are seeing.
Never trust test equipment. I had a VOM that was giving me strange readings, and I couldn't make sense of what was going on. Turned out it had suddenly gone flaky. Anorher VOM gave expected readings. Verify that your VOM is working properly. Then, if that's not the issue, leave it and go back another day. I find solutions come to me that way.
As far as the wiring goes, that doesn't look abnormal. There are shielding terminations, etc before going into the connectors.

 

It's actually a brandew VOM, but that doesn't necessarily mean a thing, there is a lot of junk out there. But I think it gave me sensible readings with the transmission speed sensors each on the right port and only there, even though I found 0.0 resistance a little too little.

I'll give it another shot tomorrow.

 

I gave it another try today and I made the following observations:

When metering the engine speed sensor wire I measured between 7 and 10 Ohm, that's way more than on the transmission speed sensors but still somehow reasonable. And I also measured a resistance of about 33kOhm on pins 1,2 and 16. According to the XJS wiring diagram 1 and 2 are ground wires and 16 is the ignition on wire. Does that make any sense? Battery was disconnected.

The ignition retard request wire only gave resistance on one port which is alright.

 

If my trust my VOM there can be only one consequence: there is a kind of short-circuit somewhere between the wires. So I tested the pins on the connector that gave me strange readings directly: and as expected, when I meter from pin 1 to pin16 for example I measure resistance of about 30KOhm. But it doesn't happen every time which could be an indication that my VOM is bad. Besides that either the connector itself could be bad or there is a short-circuit somewhere way down the wires.

 

I got me another VOM and I measure practically the same (just some deviation). So I think the VOM is not the issue here.

 

Well back again. I finally managed to get the exhaust out of the way (did not even have to cut it). My aim was to inspect the inside and maybe do the basics like new internal wiring harness, pressure switch manifold and speed sensors. While removing the bolts that hold the psm one by one, various streams of fluid came out, some rather red like the fluid from the oil pan but some also rather greyish - probably from areas where it doesn't freely circulate. The pressure sensors of the psm also had a rather slimy and grey overlay, so I think it's probably a good idea to remove the valve body and give it a full inspection and clean . I am a little concerned that I might disarrange the check *****, but now that I have gone so far I don't want to miss it. Someone gave the hint to place them with special 'mounting grease' that will hold them in place until fresh fluid will surround them (just need to source that stuff).

I also found an interesting site at sonnax where they list their improvements along with the issues it should adress. For error code #68 they offer kit #13, a plug and o-ring for the AFL filter end which should stabilize the line pressure. The standard valve does not have such a plug. At least mine does not have it.

It's just a few bucks and I think I should give it a try. Maybe along with #4 which adress various TCC issues.

While I am in there I could also replace the shift solenoids and the TCC solenoid, but I am not sure if that is really necessary since I do not have related error codes. What do you think?



Internal stuff

TCC solenoid looks good at first glance, but maybe filter screen is locked with debris?

 

The Sonnax upgrade kits are generally good and well worth doing. If you don't feel you need to replace any solenoids or pressure regulators, it would still be a good idea to clean all their screens and replace their O-rings.

Any good heavy-bodied grease should help hold the check ***** in place. I've used Lucas Red "N" Tacky successfully.

While you're in there, it would be a good idea to measure the resistance on all the wires from the main transmission connector to each solenoid or regulator connector. Sometimes the resistance on one wire will increase just a little too much, so if, for example, you measure 0.5 ohms on all the wires, except one measures 1.5 ohms, that can be enough added resistance to cause problems. Even an additional 0.5 ohm can trigger trouble codes.

Cheers,

Don

 

I’ve had the Sonnax kit and updated pump valve in my XJR for about a year now and it’s been problem free thus far. Trans fault light did come on once at some point last summer but resolved itself next start up and hasn’t come back. No clue what that was about. I only did the valve body updates with a reman’d valve body I got from EBay. Still have the hard parts for the trans internals if I ever have to pull the whole unit. I currently have the little “adjustment” plunger on the valve body set to medium firm/middle as the instructions recommend and in Sport mode the shifts are plenty firm. And quicker.

for assembly they do make a “trans goo” assembly line to help keep things together.

 

I also thought about metering all the pins now that im down here, but I do have a new internal wiring harness ready ... so maybe I skip that part and just replace the harness (if I manage to remove the plug from the housing). I think I saw some video where a guy checked his solenoids by simply connecting them to a small battery and checked whether they 'clicked' but I can't find it anymore. I think they use 12V, but I also think they won't like being directly connected to an automative battery .. so I would have to shift two small 6V batteries in a row or 4 3V batteries ... not sure.

Actually it is a little difficult to source all that stuff here in Germany or Europe, there seem to be only very few DIY-mechanics working on their GM transmissions. And not all of the US-shops ship internationally. If found summitracing, they ship international and they do have the sonnax kits and a lot of intersting stuff, but nothing else I could use (e.g. solenoid service kits, valve body gaskets, trans goo ...). Does anybody of you guys know a shop where I can get all of this at once? When shipping each part from a different shop shipping costs will overrun the actual parts costs.

 

Dived a little deeper today. Doesn't look too bad, the separator plate is in good condition, the check *****, too (didn't drop a single one). But I am wondering if I am really the first one to be in there, on some of the valve body bolts were little abrasions on the edges of the head and the bolt of one shift solenoid (torx) is almost roundish (at least after my first attempt, I better leave that one alone until I can source a replacement) - and that yellow spring of the tcc valve is yelling at me - is that color stock?


Valve body top after removal

inside, with yellow tcc valve spring

Valve body inside

little bit of pan gasket?

EDIT: While walking through all the available parts and kits I found another Sonnax kit that is related to error #68 (I wonder why this information is missing in the overview pdf): It's the actuator feed limit valve kit (#15). Unfortunately it requires drilling the valve body with a special toolkit, the toolkit itself costs about 400$, so that makes only sense for professional transmission builders.

 

Do you know/remember how the cable+plug itself is removed? To me it looks like I have to twist that corrugated ring and then just pull the connector (I had a similar design on another brand), but that ring doesn't move at all - anyway it's hard to grab it. I found videos about the GM connector and they simply pressed it left+right side and then pulled it.

 

Replaced the speed sensors, wiring harness, PSM and added the Sonnax AFL End Plug Kit but the error remains. I guess the last chance to get this fixed for reasonable money and without taking the gearbox out would be a completely overhauled, tested and Sonnax updated valve body. There is one last one left on ebay but I am hesitant to order it .. with my luck it will not cure #68 and this car just eats my money like locusts eat a field.

 

G'day V12 Lover,

I have only just stumbled across this thread as I drive a 1995 V12 but I had similar problems with the 4L80E in my car and it was the actuator feed limit (AFL) valve and not the electrics.

I had my autobox rebuilt. I had let it go far too long and as the auto tech said if I had gone to see him earlier then maybe a valve body rebuild would have been all that was needed.

This attached paper explains it.

Cheers,
Jeff.

 

Hi Jeff,

thank you for your input. Did you have specific fault codes (e.g. #68) before you had it rebuilt?
The information from your document corresponds to what I have read. When I had the valve body out I took out the actuator feed valve and had issue putting it back in what could indicate that the valve bore already has wear. My concern is that the fault has already caused physical damage to the gearbox internals (surely been doing 25K km with that fault without knowing because the previous owner had manipulated the TWL) ... or that the original cause is a bad oil pump or TCC itself. But without updating/fixing the valve body, I will probably never know. But as per my other thread, the gearbox is not my only issue at the moment ... might be buying a new saddle for a dead horse.

Cheers,
Oliver

 

G'day Oliver,

I drove my car for many years after the fault initially appeared and I had no codes at all. If I stopped and restarted the car the fault light would extinguish and the car would drive normally for the rest of the day, until eventually it didn't.

The auto tech said that the failing AFL eventually causes excessive wear on most of the gearbox valves etc so he recommended a full rebuild which I had done. The car had well over 300,000 kilometers on it by then so I was happy to have it done and I have had no problems since, 5+ years.

Cheers,
Jeff.

 

Thanks, Jeff. My car has only 120k KM on the odo, so there is hope that the internals are still ok. But on the other hand I am wondering how it can be already so bad with so few kilometers (the issues must have started before it had 100K km!). Maybe the odo is manipulated as well, the car came with little documentation/history so there is a chance someone messed with it, but the overall condition corresponds to cars with equally low mileage.