Hi Vee, how do you adjust the voltage ?

 

The TPS is a rotary variable resistor that is feed a very controlled 5.0 volt DC reference voltage signal

After it passes through the TPS the voltage is modified or changed to 0.60 volts DC on the green / yellow ECU return wire at the idle stop

By twisting the TB butterfly tower shaft an increase in the butterfly opening will modify the 5.0 volt reference signal voltage less so the modified return signal back to the ECU will be higher then the 0.60 and climb toward but not to the 5.0 value

to adjust the return signal you would loosen the TPS mount bolts and rotate the TPS this way or that way and then tighten the mount bolts

You might find the fresh TPS has no adjustment so you would remove and drill the TPS sensor body mounting holes bigger

At the factory off the production line the " fixed mounting "of the TPS is oriented electronically in the ECU though special equipment to make the fixed mounting return voltage value the new null value

null is a sensor return reading reference to a point of interest in this case a closed butterfly

This could be 0.59 or 0.62 volts DC

To make things confusing you will not see below 13 % as another reference value on the TPS at idle stop with the ELM 327 reader ( common available but not needed in this specific area of TPS orientation )

Dealers will not touch the car without the special electronic equipment as they only follow official jaguar procedures and test as a follow up after repair the same .........

But is a basic engineering work around without the fancy muchene

Contributors on this website have figured out a way around the muchene

 

Parker nailed it....as usual.

 

You can play with the TPS with the engine not running but the key in the run position

Your final check will be an engine run

This will keep the TPS powered with the 5.0 volt reference voltage and you can nick the insulation on the Green / Yellow wire as it passes over the fuel rail

On mine the TPS connector wire locking clip was missing and you can pull a spare locking clip from the trunk dome lights

 

Is it possible to re-set the ECU which should be looking for any resistive value as (at idle), regardless of differences in value for the old part and the new one ?

 

I understand what you are saying

But not that I'm aware of

 

that’s what the jaguar diagnostic tool does. if you don’t have access to it you’re going to have to mess around with a 90 degree torx handle till you get an idle you like

 

Someone who knows more about matters electrical than me, ie most everyone, but most likely Parker, can maybe answer this. Would the solution to setting the idle not be to wire a variable resistor into the TPS circuit, allowing you to "dial in" the idle speed of your choice by adding or subtracting from the TPS generated figure?
The Dealer diagnostic software seems to be unobtainium for many of us, and the ability to introduce adjustment via the TPS fitting lugs is of little comfort to XJR owners, whose TPS is extremely difficult to access, rendering an iterative approach likely beyond the limits of human endurance!
Probably a dumb suggestion, but I thought I would ask.

 

Not sure you can make something easily that would be adjustable to that degree. We are talking 0.01 of a volt!

 

You could presumably use another TPS, of a less expensive variety?

 

There is no known alternative to the expensive, necessary part!

 

I know that.

The objective of my suggestion is to create a means of adjusting the output from the TPS to "fool" the ECU. Sort of similar logic to the Andy bracket.
An additional TPS wired in series, but remaining in a fixed position once set might achieve the adjustment to the TPS output the thread seemed to be craving. Your previous objection was that it wouldnt be possible to find a resistor which could be adjusted to affect the signal to the ECU with an accuracy of "0.01v" . Surely a TPS can do precisely that?

 

If you wanted to put something in production, like a kit, to sell to others, I believe you would find plenty of people that would pay you to "reset" their TPS' as a plug and play kit.

 

This proposal would be a trim pot

We used them on jet engines

But the trim pot can only add resistance and not subtract

 

Yeah, I'm not sure there is a device that can subtract resistance.

 

all you need to do is construct one that spins backwards or find one from another car if it exists

the jaguar part is a ford cologne TPS in reverse

 

Ding ..........

You can change the sensors input voltage to say around 4.5 or 5.5 volts DC and leave the reference ECU 5.0 volt DC wire cut and isolated

You would leave the TPS in place and operating

You can put the device in a Tupperware container like a catsup container to waterproof it , control knob inside


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And there is often contributor Youtube , see minute 4.00


and




YOU GET TO TRY IT FIRST !!!!!

 

The most prevalent issue seems to be idle speed too high, ie voltage too high, so subtracting resistance would not be necessary or relevant.

 

His idle speed seems to be correct just rough so that would steer you away from the TPS signal being out of target but then it can be an issue of.............things not being in physical place like a valve not being in proper place like a partial open and not fully closed butterfly

And then there's coils which is a money item unless you can justify it based on their age / mileage

Was this the example of the TPS signal of 0.54 volts at idle ?

 

There have been numerous threads that found the coils to be causing problems once they are hot.

Buy a cheap set to see if that cures the problem?