Hello everyone

As I mentioned, I finally got my 95 XJR running, after 4 years, due to a sheared woodruff key, ( go figure ) anyway the tach stopped working within a few minutes of starting. It still starts and runs fine, just no tach, I know it is not the cps, as it still starts and runs ( and I replaced it, with same results ) I also swapped out the ecu as I have a spare ( also no difference ) so does anyone know where and how the tach gets its signal from. The car drives fine but it trips the transmission light, and throws codes
P1775 (general transmission fault ) and
P0726 ( engine speed input circuit range/performance ) and
P0727 ( engine speed input circuit no signal ) as from what I have read on this forum the trans light and code 1775 for the trans would be expected as the trans says its turning, but it is not matching the engine rpm, as it is not getting the signal that the engine is turning. So the tach must get its signal from somewhere other than the cps. I have been searching the forums for answers. I even have the useless disc from JTIS but I am not able to find anything usefull at all.

Any ideas, if its just a bad tach that would be good, but I find it hard to beleive that the transmission gets it engine speed signal from the tach

Does anyone know

Darryl

 

Darryl:
It ain't so simple- The "tach" is an electronic function that is absolutely DERIVED from the CKPS, (not the CPS). Obviously your CKPS is working or the car wouldn't run. I am not at my computer with the diagrams, but I am pretty sure the ECU, which gets the CKPS signal, sends the derived speed to the instrument module and the transmission module over a network connection. As I said, I don't know the exact connection on an X-300 but I will look it up in a day or two for you if someone else doesn't chime in before then. In the mean time, i would look for loose plugs on the TCU and the instrument module.

 

I just came across this same issue this morning! As I'm heading to work, I noticed that my fuel gauge was on Empty (which I definitely didn't leave it at), and my gauge for coolant temp was all the way down (assuming the car still needs to warm up). So i'm driving to the gas station when I notice that none of the needles are moving on the Tachometer or other gauges. I was hoping to see that this is a simple fuse type of situation, but i'm not to savvy on cars when it comes to the electrical lingo. If I could get a hand from anyone it would be appreciated!

 

hello sparkenzap

In my post when I said cps, I ment the crank position senser, that is what I replaced, and as you noted it starts and runs fine so it has to be working. I will continue checking conections for trans and such.
It did the car no favors sitting for that long, it had a bunch of issues the first couple of days, ( traction, abs, etc ) but all that seems to be left is the non working tach and trans light.
I really appreciate everybodys help

Darryl

 

hello sparkenzap


I was wondering if you found those link connections for the tach, I did check all the transmissions connections, the 3 at the tranny and the TCU. It is still running good, just no tach and I have noticed that the fuel gauge every once in a while wobbles a little bit, I would think that it is just a instrament pack issue except for the fact that it trips the trans light and and throws the code for no engine speed signal, and like I said before I cannot beleive that the trans TCU gets its engine speed signal from the inst pack but I guess it is possible,
Any ideas anyone ?

Darryl

 

I know is an old thread, but was this issue ever resolved? I have a 96 XJR with similar symptoms. It runs and drives pretty good but the tachometer doesn't operate and the transmission fault light is on. The check engine light is on with a fault code of p1775. I have replaced the crank position sensor as maintenance but that didn't do anything for it.

 

The crank signal is an input to the ECU. That is obviously working as the car runs.

There is a single output of engine speed from the ECU to the Tans, Instrument Cluster and AC. I'd be suspecting a dodgy ECU plug/wiring. Check for moisture and corrosion in the plug and check for signal out of the ECU.

The pins to check etc are in the Electrical guides that can be downloaded from the links on forum stickies.

 

My most recent X-300 and number of other reported cases have had corroded pins on the ECU. That's the module in the RH front kickpanel. I would look there first.

 

Hello to all, I just got a couple of emails from the site regarding this post. ?

so here is what I have found, there is one wire ( purple ) that comes out of the ECU that then goes through some connectors and then into the Transmission ECU and then back out of there and then into the climate control ECU ( these are all in the passenger foot well ) and then it goes up to the tach. ( the wire stays purple the whole time in and out of each component )
This is the engine speed signal wire it is supposed to have a specific frequency at a given RPM at 5 volts and then that frequency changes with RPM ( I do not remember the numbers right now, this was quite a while ago, but those numbers are in the manual ) So I bought a small cheap oscilloscope for like $100 to see what the ECU was putting out. And guess what it was putting out the exactly right signal, as was every link in the chain, ( every connection, every component all the way to the end at the tach )
I then checked the signal on another Jag and it was the exactly the same. I then pulled the instrument cluster out of both cars and swapped them, and the non working one works just fine in the other car, and the working one stops working in the problem car.
I should mention at this point that all 3 components involved do not work correctly. The transmission will not shift into 4th gear, and the climate control system does seem to know what to do regarding temperature so most of the time blows cold air not the set temp. But if you put it in diagnostic mode everything in the system works and it makes heat.
So there you go I spent a huge amount of time on this issue and still have no idea.
But I hit a deer recently, so now the car is totaled so it is a mute point for me. Sorry I cannot be more helpful.


As an aside I wanted to let everyone know that I had a leaking diff issue, so pulled the whole assembly out and pulled it apart and found the spider gears were galling, so you cannot buy them alone ( of coarse ) so you have to buy a whole rebuilt diff $$ or a used diff to get the spider gears out of ( with no gaurentee they are any good ) and it seams nobody know anything about the Sailsbary diffs in these vintage jags, they nobody even seems to know who actually builds them. we all know that the older Jag diffs had DANA 44 guts but after 1987 it seems to be a mystery. So the other option was to buy a new after market unit for a DANA and see if it would fit. So I bought an brand new Auburn limited slip unit for a DANA 44 for $140 and took it to a locale diff shop, and told them to see if it would fit, and I am glad to tell it does. So with bearings and seals and install for another $ 400 or so. Way cheaper than $1600 for an exchange rebuilt unit, even though you nobody sells spider gears to rebuild them with.
So spread the word that in the XJ & XJR 95 to at least 97 and probably 88 to 94 as well that you can just put in an Auburn DANA 44 unit.

Darryl

 

Climate Control module uses the speed signal to modulate fan speed to compensate for ram-air pressure. So it wouldn't have any sensible effect on temperature - beyond that you'll get more of what you're asking for (hot or cold) as the airflow through the evap or heat core slows down, more heat-transfer will occur....but I digress...to determine if the speed signal is "Knackered" as far as the Climate Control is concerned, look for your fan speed to not speed up when you come to a stoplight - not always noticeable, but frequently so.
I realize you are apparently done with the car, but post for anyone else fighting this problem...thanks for posting back the follow-up!

 

When we last left our poor 95 XJR, it had a poor deer commit suicide by throwing itself at the front of my car. anyway I sold the totaled car to a friend, who is a body-man and a boat electrician. Anyway he chased the problem as well, and after looking at the wiring schematics and on a fluke he thought that a lead from the ecu winds up in the boot and goes to a relay , anyway he swapped out a relay in the trunk and ta dah everything worked, the tach, the climate control, and the transmission.
So anyway he fixed the car, and I bought it back from him. As I really liked that car, it is black/black in very nice condition and it only has 125K miles on it.
And I had just put new tires on it and completely rebuilt the diff ( Auburn DANA 44 unit, spread the word $150 ) and rear hubs and rear shock bushes before the deer hit me.

I just wanted to let everyone know the solution to the problem, to add to the knowledge pool

I do have a couple more issues with it, the passenger side half shaft was bent pretty badly ( I have no idea how ) so I got a replacement ( used ) it was also bent, so this causes the hub and wheel to wobble which is annoying. But the biggest pain is there is a vibration/groaning coming from, I believe the drive line. When I had the diff out there is a bearing in the diff end of the drive line, which was pretty bad, and the stinger that part of the pinon gear that plugs into it was also pretty crappy. But as it is part of the gear set, I left it alone. Anyway I replace the rubber flex ( after market)between the 2 and it seemed worse, I tried all 3 positions ( phases ) all bad so I put my old one back in. I think that is my problem, but any thoughts would be appreciated.

Darryl

 

Hi Darryl,

Do you happen to know which relay in the trunk he replaced? Any specifics would be helpful to others.


Do you mean that you put Auburn DANA 44 internals in your original GKN Salisbury diff case?


That wobble is also putting a lot of extra stress on the differential output shaft bearing, so you may want to find a good straight half shaft soon.


I had the same problem with a new flexible coupling from Uro Parts. It would not balance in any of the three positions (and I also turned it 180 degrees and tried the other three positions). I sent it back and ordered an OE GKN coupling and it balanced on the first try. Here's a link to some photos:

Jurid Flexible Coupling Replacement

Cheers,

Don

 

I am sorry I will try and be more helpful

Regarding the tach what I was told, was that on the R anyway, there is 1 relay ( which I believe is for the WOT secondary fuel pump on the R ) and 1 module ( unknown what it does ) that are located on the forward bulkhead of the trunk, in front of the battery. Apparently these 2 had been switched with each other. I have no idea how. they apparently have the same plug, so this is possible.

Now regarding the differential, since I could not find the spider gears and I really did not want to spend $1,500- 2K on a rebuilt one. Especially since no one sells new the spider gears, I am a little dubious of the rebuild quality. And since no one could or would say for certain what the diff is in the X300 car other than it is a Salisbury. I spent a lot of time researching ( trying )So I took a chance, that the internals were probably the same as earlier Jags, anyway the Auburn company makes limited slip units for the DANA 44 for cheap $150, you have to get the one with correct output spline count ( I forgot what the count is, but it is the coarser of the 2 types made ) Anyway the Auburn unit works just fine in the Salisbury unit, in the X300 cars. I had a locale 4x4 shop assemble and set up the gear lash and they charged me around $300 labor and for all the bearings and seals. So I think that is good to know that.

As far as the half shaft, I know I need to get a good one as it will wear out things.

I did see your write up on the jurid rubber ( very well done by the way ) Like you said the URO brand seemed to be a problem, I just ordered the OEM part, Hopefully that will solve my vibration issue.

I hope this clears up any confusion

thanks for your help

Darryl

 

Hello again

I did buy another used half shaft to replace the bent one, and had it checked at the drive line place and they said it is also bent, but they believe it is better than whats on the car. So I will be swapping it out. A big question that I have is how in the hell are these getting bent. There is no way that anything could get up in there to hit the half shaft to bend it and there is no way to put a jack on it to bend it. And there is no way there is enough horsepower to bend it, so what the heck.

I also did replace the jurid coupling with a factory part trying to get rid on the vibration and humming, but it made no difference.
It vibrates the whole car at speed and is quite loud. I jacked up the car and got under it with stethoscope, and it is not as loud outside the car, but the whole diff sub frame is vibrating and most of the noise is coming from the passenger side hub area ( this is the bent half shaft side ) but it is hard to believe the slightly bent haft shaft and corresponding rear hub wobble could make such a vibration and noise. it just seems that the frequency of the vibration and noise is spinning way faster than the wheel speed. But the drive line and center bearing seems fine, and make no noise.

If we are ever able to get rid of the noise, we will have to get a new name for the car. Right now it is the Hummer.

The AC has stopped working as well, leaked out Freon, so I replaced the compressor, and sucked down and recharged, blew cool for a day, leaked out, put in dye, can find no leaks in engine bay ( bummer ) as I know stuff the evap inside the car is going to be a bugger. Wish me luck

 

Hi Darryl,

In over 20 years of Jaguar ownership and maintenance, I don't think I can recall anyone else ever reporting a bent halfshaft. That is truly mystifying.

Have you thoroughly checked the condenser? It's not easy to access and may require removing the grille, displacing the radiator, etc.

If the evaporator is leaking, you may be able to detect the UV dye in the condensation that drips down the drain tubes on either side of the transmission tunnel and through the floorboard. Shine your UV light on the water that drips underneath the car and see if you can detect the telltale glow.

If you confirm the evaporator is leaking, the dash is not as difficult to remove as you might think, it's just a little time consuming. I believe the instructions can be found in the Workshop Manual/JTIS.

Cheers,

Don

 

Darryl, From the description of how your car is shaking, I'd say check to see if your lower condenser mounting bushes are intact (uppers too, actually.) If not, I'd bet your leak is in the condenser! Check the back, right side, a little more than half way down. Also trace around your a/c lines and components looking for evidence of oil where it ought not be. Full charge in one day should probably leave an oil trail.

 

I agree, I do not understand how the hell they are getting bent, if I have not seen it with my own eyes. And the other interesting thing is they all are bent in the same area about 4 inches inboard of the outer u-joint. But even if I find and unbent one, I have little faith at this point that it will solve the humming and vibration. And how do you find a straight one ? As I have now bought 2 used ones and they were both bent. And at $70-100 a wack.

I am happy to hear that the evap job is not as bad as expected, maybe I will fix and keep the car. My wife really likes the car, but insist on AC working.

Darryl