This was the reasoning someone else explained (on this forum - but either this or the limited slip topic under "engines" board)...

Only the imput shaft is measured to allow a significant range of option in tire and wheel sizes. The way the computer knows if the wheels are spinning (lost traction) is by measuring the speed each wheel is turning in relation to each other - and in relation to how fast the rear wheels should be turning according to the rpm IMPUT transmission shaft (only). If one is turning too fast, then traction has been lost. If the rears don't match the engine speed, then traction has been lost (such as on ice).

That poster (Brutal or Avos - can't remember which - I think anyway) states this is why you can go to smaller tire diameters all the way around that - in a sense - does relatively speaking lower the "ratio." (also lowers the car and changes appearance plus buying different wheels and tires - but smaller is much cheaper too.) BUT while you can go to smaller tires, you cannot go a different ratio because then the tires are turning at different rates - indicating lost traction and therefore putting the car into the "limp" mode. The computer also MIGHT be calculating speed to rotation ratios of the rear wheels (but the "trick" would also hide that).

That is how it was explained. That is why I speculate that if you "trick" the computer imput from the sensors on the two back wheels by the same signal/pulse (or whatever it is) ratio as the gear change ratio, it might then have the computer seeing no change at all. If I lowered the gear ratio 30%, but also somehow cut the rear wheels signal by 30%, the computer couldn't know there had been any change IF only the imput shaft is metered as has been claimed. It couldn't know the rear tires were spinning faster.

HOWEVER, then it MIGHT be necessary to do the same with the front wheels??? as now they are not at the same rate of rotation? Or maybe that is the complexity? You can't trick it in one regards without creating imbalance in another regards?


If speedo adjusting "boxes" do so, then it would seem to only require two of them. That also would seem to mean the ABS etc shouldn't be affected - though that ABS system isn't really a concern of mine.

OR... WHAT ABOUT THIS IDEA???

Why not just have the sensors all reading off the front wheels? Can they be doubled over like that? Just have the "wires" for the rear wheels' sensors instead spliced into the front wheels' sensor outputs? Wouldn't then all 4 wheels be consistent AND no gear ratio change detectable? This would kill traction control but I don't care about that.

How would the computer know where the signal is coming from? Could whatever says "back wheels" be put up to the front wheels instead? Just have all 4 imput signals/meters measuring only the front wheels.
Would the signal strength be reduced detectably?

Since a computer can only know what it's "told" and that is coming in on a wire - trickery seems the solution. The computer can only see what we let it see and it will only see what we show it. Why not show it the front wheels and tell the computer it's the back wheels by moving the "information line" from the back to the front?

A parts check might answer this. Are the "sensors" parts the same for the front and rear wheels? If they are the same, then the computer cannot know which wheel it's monitoring and receiving the signal from. It only knows what line it's coming in on. One of the members here with access to such parts listings should be able to look that up.

(that's a funny idea... add a "5th wheel" to the rear that is OEM diameter and have all 4 sensors read it. Then the computer would see the car as being in perfect harmony with the world's more cautious driver.)

 

You wouldnt be modifying the wheel speed sensors output, as stated previously that would effect all of the processors and you only want to effect the TCM. You would want to modify the speed signal somewhere after the instrument cluster, and only on the trans speed sensor input wire, so it wont alter any other computers inputs. And we cant even try that with out knowing what protocol the TCM uses.

 

I pulled my 05 XKR onto a wet patch and punched it with traction control off. But rear tires burned the asphalt and appear to have done so to the same degree. I agree posi is a necessity. Don't I have it? Seems like it has it.

 

Unfortunately there is no posi on any of our cars as they came from the factory.

 

There is no trans speed sensor input wire.

The whole car is CAN bus. It's a two wire serial common data bus. The wheel speed sensors are wired to the DSC module. After that the DSC module broadcasts the info over this bus. There's no way to grab the signal after the instrument cluster or anything like that.

The days of input wires at each module are long gone

Now DWFX. There seems to be a LOT of confusion at there. No car can break the laws of physics. Not even a supercharged XKR! (Even though I would be appreciative if you let me borrow it in a valiant attempt to try!)

First as far as signals from the front wheels or back wheels it doesn't matter. Since the car is traveling at a consistent speed at any instantaneous moment ALL 4 wheels are turning at the same speed. Unless the tires are different physical diameters. So that would make no difference to the computer, other than to possibly fool the traction control into never thinking the rear wheels broke loose, (there's a switch for that already) and having abs only kick in if the fronts are about to lock. There is no way for the car to have the front wheels turning slower (or faster) than the rears other than in a compromised traction situation.

Once again the problem is there HAS to be a road speed comparison.

"according to the rpm IMPUT transmission shaft (only). If one is turning too fast, then traction has been lost. If the rears don't match the engine speed, then traction has been lost (such as on ice)."

Here's the thing, the rears don't turn faster on ice at any given engine speed. What happens is that not all of the rotations are transfered into forward motion hence wheels "spinning". The engine speed remains the same. The transmission is a mechanical system. For each engine speed and gear, the output shaft (and driveshaft) turn so many times. What the car realizes is your front wheels are going 10mph, and your rear wheels are going 40mph, hello, loss of traction. The differential is also a mechanical system. Each rotation of the input yoke equals a fixed number of rotations of the axles.

The only hope would be that You would have to do all 4 wheels, by the amount of the gear ratio change, to get the computer to think that all is well. The problem with that becomes erratic shifting, and all sorts of other confusion (torque converter lockup points, gear choice etc)... It's going to shift as if its got the shorter rear in it. Among other things.

These boxes are designed for simpler cars, that just use the output shaft speed sensor (which is external and has a wire harness on it) or the wheel speed sensor, as a source of vehicle speed for the instrument cluster, simply to correct the speedometer to adjust for different gears / tire sizes. What we are trying is much, much more complicated than that.

I STILL think a software swap in the trans, with another model of jag that has a different rear end ratio using the same trans is the most viable option. Once again this is contingent on finding a dealer who will play nice. I don't know if the IDS system reads the vin of the car it's attached to or that is inputted externally. If so it would be a matter of just supplying the donor vin and only doing a trans flash.

The thing is, no one has reverse engineered the Jaguar IDS system. And created a stand alone reprogrammer, or software It's Just not profitable enough to do so.


George

 

"Posi" is slogan. LSD. Or was it magic to spun both wheels?

 

Must have been magic, or some really good LSD.

 

I just found the ultimate 500 horsepower boost for the XKs. And it's an easy install...fits on the trunk.

 

Is a stand-alone engine management system an option for the XKR?
It's starting to seem like the only way to get serious performance out of an XKR is to revert to Americanizing the motor and transmission - if even that is possible without having to also replace the instrumentation, window switches and about everything else, basically using the bare chassis and going from there.
The solution to my XJS was a BBC 454. Is an SBC the only solution to an XKR?

 

Hmmmm... Should have bought yourself another car dude................

 

If Jaguars,like corvettes, were made out of "plastic" they would be just as quick.

 

Sheesh, what a painful read this was.

Where do I submit my refund request to get the last 25 minutes of my time back?

Time will solve all your issues.

 

Thanks for dragging up a 4-year old thread that was dead & buried...

No need to re-hash this, thread closed...