One min here... If we disconnect the wheel speed sensors. What happens. Car throws ABS / DSC codes, and you loose the speedo right?

You don't throw any transmission codes do you? (That's the key...)

Now If you could change the cog gear on the output shaft sensor in proportion to the change in rear end ratio, the trans would be fine (no codes, because it thinks the stock rear is back there). That's the same idea as modifying it electronically.

The problem with that again, is dropping the trans taking it apart, on the "attempt" that it will work.

My money still goes on a rear end from a different model with a higher ratio, along with the appropriate trans flash. Non intrusive, and can be reversed.

George

 

"Now If you could change the cog gear on the output shaft sensor in proportion to the change in rear end ratio, the trans would be fine (no codes, because it thinks the stock rear is back there). That's the same idea as modifying it electronically. "

The TCM checks also the internal operation, by comparing the Input Shaft Speed (ISS) to the Output Shaft Speed. If you alter the OSS, you will get an error is the TCM sees a mismatch in ISS compared to the OSS. That is why modifying the OSS signal will not work.

"My money still goes on a rear end from a different model with a higher ratio, along with the appropriate trans flash. Non intrusive, and can be reversed"
There hasn't been a different rear end ratio for the 4.2 XKR. And even if there would have existed one, you would have to fiddle around with the software (the IDS doesn't let you choose the files to update, it picks files depending on your VIN) and probably change checksums etc, could be tricky.

 

The TCM Fires an "output shaft sensor error" when the rear is changed no? Isn't that the whole source of the inability to swap the rear end out?
as far as that, I haven't played with the dealer computer, but if you had the vin of the car with the donor rear, could you just flash the trans?

I'm speaking from a theoretical engineering standpoint here, I have no experience with the particulars of the Jag software.

George

 

yeah that is what I was trying to get at. But you would have to know what language it speaks when sending the signal from the speed sensors. That could be tricky as each processor could have its own protocol.

 

For a couple of hundred dollars you can buy devices that are able to read the CAN bus, and also decipher most of what is going on. You only need to focus on the TCM, as you would only want to alter the values that the TCM wants to pick up (if let all signals go thru the device unaltered both ways, except for the wheels speed values). CAN bus is used all over the work, so am sure you will find people that can help there/ give an idea if such a device is possible.

 

I still think the whole coversation is moot. These cars stock with the traction control off can boil the "tire" at will. So you wont get as much from lower gears as you will from just adding the limited slip. AVOS you can chime in on this, but I would expect to see a great improvment in 0-60 times just by getting 2 tires to hook up, even with traction control on. When I bought mine the diff had a warped ring gear, and while I was calling around to get parts, I heard they have soft gears anyway and that it was common for them to warp. Until now I had never seen a car warp a ring gear before. I have rebuilt at least a few hundred diffs in my day and this was a first for me.

 

I hope a solution is found. Performance is only one consideration. The other is the "asthetics" of tight gears...

I don't mean to make dunderhead speculations as computers at this level are beyond my understanding.

From what I'm reading, the TCM is making calculations upon three info-sources. 1. The rotation speed of the transmission imput shaft, 2. obviously what gear the transmission is in and 3. the wheel(s) sensor(s) sending information of how fast the wheels are rotating.

It would seem trying to alter the TCM or it's monitoring of the transmission is impossible or to great a hurdle to experiment on. But what about the information being transmited on wheel rotation? Can that information be electronically altered?

It would seem that the "interception" point for any electronic manipulation of the TCM would be between the wheel sensors and the TCM (since the TCM is internal and seemingly otherwise unalterable). It shouldn't be impossible to know which wheels are sending the rotation information to the TCM and across what "line/cable" it is being transmitted. Couldn't one of those speedo modification modules be put between each wheel sensor line (however many there are) to the TCM - basically tricking it?

If the info to speedometers can be electronically altered, why could seemingly identical information comes from wheel sensors to the TCM also be altered? (this would, however, also then alter shift point rpms to a lower rpms?)

 

OK you CAN modify the output from all the wheel speed sensors, with these electronic modules but that's about it.

You can't pick and choose which module gets the original or modified signal, that's not the way it works in a can bus setup, every module will get the same info. Basically the way can bus works, is it's broadcasting messages.

Picture it almost like FM radio. Basically you have a bunch of stations across the dial. Country, rock, talk, etc... And all day they send out info (its not simultaneous but rather at fixed sample intervals, although some messages are coded specifically for their destination, i.e. turn on the lights) . Now the other modules in the car are the radios. The TCM wants to know wheel speed, it tunes into the wheel speed station (basically listening on the bus for the wheel speed message, ignoring the messages that the cd player is telling to the amp to turn up the volume or the door lock telling it to unlock etc).

With the data bus, the only way is to intercept the data heading to one module, and recreate it altered. There's no way to create separate wheel speed signal depending on which module u want to have them.

 

I think that's what I'm wondering - can the output from the wheel sensor(s) be modified. How do speedometer modifiers work? Isn't it the same principle?

 

@androulakis

It is a bus, the CAN bus goes into a device, and also out again via different ports.That means that you can put a device in between, so with this you can affect the signals specificaly only for one device (TCM) which you want.

 

Amen, as lomg as you speak the correct protocol

 

So it would be a matter of finding out what wheels are being monitors, mounting and connecting in the speedo-adjusting boxes, calculating the ratio change and then seeing if it works after changing the gears? Sounds like a $5,000 experiment.

I still don't understand how the TCM could distinguish between spinning (smoking) the tires with the traction control off and running a lower ratio with the traction control off. Both have the rear tires spinning faster than the car is moving. If it will allow burn-outs/smoking the tires, how would it know to stop wheels turning too fast for the speed with lower ratios?

Is anyone certain that simply turning off traction control doesn't solve this? It's not something Jaguar would reveal, but it is a puzzler.

 

It isn't just about smoking the tires from a standing start and OEM-type hard rubber tires aren't the only tires that can be fitted. What about at 50 with 12 inch wide soft tires? There also is the aesthetics of the sound and feel of tighter gears, better "motor braking" etc.
Under the premise that they are already over-powered, that then would also be to claim that increasing horsepower also would be moot.

 

See Here's the thing with your burnout scenario.

The car KNOWS it's doing a burnout.

Sees the front wheels spinning at a slower speed that the rear wheels.

The trans is still fine (input shaft v/s output shaft revolutions). And the rear wheels are traveling at the proper speed (albeit with the car not moving or traveling much slower) that they would be if there was traction.

That's one of the conditions the traction control senses to decide to intervene.

When you turn it off, it simply lets you sit there roasting the tires.

The problem is when the car is traveling, and the wheel speeds (all of them, equal) DO NOT match up with the expected rotations of the trans output shaft. The trans thinks its slipping.

All of these wheel speed sensor modifiers are analog in nature. The DSC module converts these to can bus digital messages. All you could do is permanently "lie" to the car about the speed that all 4 wheels are traveling with these devices.

George

 

Thanks for the comments/expertise sharing.

Any reason not to lie to the computer? (in short, is it likely to work?)

Wouldn't it only be necessary to lie to the computer about the back tires/wheels? There would be no change upfront.

 

Since there likely already is a thread somewhere on this (searched, but couldn't find it), I don't want to start another one.
Changed the oil (Royal Purple 5-30), the oil filter (K&N) and air filter (K&N). Glad I did, there was a large piece of styrofoam up against the OEM style filter (?) The old paper air filter was like new.

(OH, BTW, oil fill shop online sources say the XKR only uses 7.4 quarts, where the manual says 8.2. The dipstick confirmed 8.2 - so people using oil-fill shops may want to be cautious - AND WATCH THEM! Even though I gave them exactly how much I wanted put in, they only put in the typical 6 quarts at first but I was watching them.)

Discovered I do not have the tire-air filter fitting and the cover is missing off the fuse box. Trying to find a little thing like the tire filling fitting is annoying stuff. If I come out to a low tire I'm just grounded.

What I couldn't figure out is how you fill the tranny. Found the drain plug. Is there a thread on how to fill the ZF6 speed (05 XKR)? Fluid to use if I do?
(Lack of being able to find a shop manual is becoming frustrating. I'm having to make educated guesses. Would a shop manual for an 02 XKR be mostly correct?)

 

See remember wheel speed is different than output shaft speed. This is how many revolutions the wheels are turning. What a different rear end does is change how many times this happens per revolution of the driveshaft.

The problem is lying to the computer isnt going to help unless for one specific scenario:

The TCM compares input shaft speed v/s output shaft speed v/s road speed. And that is what is causing the faults. Is it likely to work? Without looking at the actual trans software coding and determining the algoryrhms it uses to determine faults, the honest answer is I don't know...

You can't just lie only to the rear. First its gonna throw off all kinds of systems / abs/ dsc / trac etc...

It would be creating a permanent condition (from the computer's standpoint) of the front wheels turning at a different speed than the
rear wheels.

My other concern is would you throw a different fault code, whereby is there a calculation for / engine rpm / gear selectoion (of the trans) v/s road speed. Since the engine is going to be turning higher RPM's at any given road speed, will it throw a fault on the input side of the trans, or make the trans think it's slipping internally??

George

 

Horsepower is never moot. But I think if you read the post a litle closer, I said "Tire" not tires. Double the traction would in my opinion be the biggest upgrade at stock horse power ratings. Period.

 

Others have posted that only the imput shaft speed is measured.

 

Then how would the car know it's got the wrong rear in it? If the trans isn't slipping the driveshaft is still going to turn the same number of times in each gear relative to input shaft rotations. What changes is how many times the wheels turn with each rotation of the driveshaft...

There's more than that going on.

George