I spent the day mucking about with throttle position sensor on the 87 V12 HE - and I'm forced to conclude that the posted set up accuracy for these things (0.32 Volts plus or minus 0.02) is simply not achievable. I guess I'm challenging the posted wisdom which I think comes from A6 engineering as it is based on their TPS with two mounting screws.

I have two position sensors and two throttle capstans, neither make any difference. Just touching the capstan is enough to have the voltage bounce around, simply resting a finger on one of the ***** that the rods attach to can vary the voltage between 0.24 and 0.37 volts.

Even if you do get things on the nose they're not repeatable, I thought it was simply the busted shaft but it isn't.

Does anyone know where this stuff is documented in the Jaguar stuff - I can't find the TPS setup described anywhere other than using an external adjuster box until the lamp illuminates.

I've since put both throttle capstans on the bench and the best I can get is plus or minus 0.07 using a regulated lab PSU set to 5 VDC but the instability is still there so simply putting the rods back on will affect things, if one rod pulls slightly ahead of the other it affects things - doesn't need to move things just apply pressure.

Regardless of the tower or TPS I use the tolerance of 0.02 simply isn't possible - don't suppose anyone has one of these anywhere so that I can measure what it is doing. I'm struggling to believe that something so crude can expect 2 hundredths of a volt accuracy.

 

How old is your TPS? I have found the setting to be repeatable with a new TPS.

 

Both are quite old, the problem seems to be more mechanical in nature. The sweep from 0.2 all the way through to 5 Volts is clean with no steps, the problem seems to be the shaft that's turning it. Although it is hard to detect by hand a DTI detects it easily, if anything the 'old' TPS's are way too sensitive to mechanical side loads on the shaft, one throttle capstan does it worse than the other but I don't see any way to take out slop.

I may buy one from A6 just to check it out - if he ever returns a call - been trying to get a response for a week now, otherwise I'll just get creative and build an electronic filter - give the ECU 0.32 for any voltage below some threshold off the TPS - say 0.37 - it would help to know just what the ECU expects. I believe later ECU's (32CU onward) had a much higher threshold - 0.75 with a recommendation to set at 0.6.

 

I had the same with my old Bourns TPS units.

Managed to get them "so so", and lived with it for a short time.

New Bourns, back in those days, were $450, not happening.

I went way off Jaguar Reservation and found a Mazda TPS, that rotated the same direction, and had 100deg of rotate, adapted that, and went 2 years.

Then I found the XJ40 TPS, spring loaded to zero return, and adapted that, and never touched any of them again. Benn 20+ years.

Did an '87 here years ago for a mate, and got is acceptable. Did not flex as you have, but a tad flaky, and he accepted that, as its a 3 times a year car, his choice.

 

Can you address how you adapted the XJ40 TPS? Some the ones I've seen have more wires. Or is there a three wire type? What did you have to do mechanically?

 

AJ6 do not sell TPSs any more. A new one will cure the problem, either a Bournes type one from Manners or a new red-style one. I think it is just that the old ones are worn on the shaft carrier bearing (or whatever they have to hold the shaft).

 

PDF attached.

Wrecking yards, my 2nd home years ago, not so now.

You will need the NO USA TPS, as it has 3 wires, and a NO electronic transmission. XJ40, 3.6 and 3.2 ltr is the go. That larger 4ltr one could be used if you took the time to isolate the 3 wires for the EFI, and insulate the other trans control wires, too hard for me at the time, with plenty of the others available.

Mechanically, nothing, fitted, as per the PDF, drank beer, drove the thing, simple, AND, this was before Internet and Forums, so I was using Aussie common sense, HA, sadly a dying commodity these days.

 

Thanks for the info. That explains why the TPS I see for the XJ40 in the US have more wires. Right now, the upgrade TPS for the XJS is cheaper than the multi wire XJ40 TPS'.

 

Thanks all - clearly I have even more unanticipated project opportunities and expense .... oh to be ignorant and not so OCD about stuff like this - wonder if I'm cut out to own an older 'project' .... will I ever get it done.

 

I'm wondering if you have adjusted the rods and butterflies to have zero slack, since you apparently have mechanical feedback from the rods ?
You are supposed top have a 2mm spacer between capstan stop when you adjust the rods to zero slack. Then you remove the spacer, and the capstan needs to rotate 2mm before it actuates rods.
I have no problem adjusting my red TPS. I changed TPS to a new because I had other problems, and still adjustment was easy and stable.

Good luck

 

There is NO smoke and Mirrors with the TPS, or ANY TPS for that matter/ It is a device to split a 5v signal so that the fueling ECU can do what it is programmed to do.

I looked at many in that wrecking yard, about 4 beers worth, and the Mazda was the one. It took some adapting, but it worked for 2 years, and was still sort of OK, when I stumbled on the XJ40 units in the same yard, whoopee, and $10 each, thank you very much, see ya.

The rest is history.

BUT

The TPS selection today is wide open, I mean Carby cars were still very much in vogue when I did mine.

 

This is on the bench .... this is axial play in the capstan affecting the potentiometer, not even on the car where it is worse, slight pressure from a finger is enough to exceed 0.02 volt tolerance. I am following Grant's do do list and have all the manifolds etc off the car whilst I clean and refurbish hoses etc.

You can set the thing but it isn't repeatable - meaning if set to 0.32 and rotated a few times it should come back to 0.32 consistently - it does not. I have two capstans, two position sensors and both have this problem, both position sensors work just fine off the capstan.

This is a direct result of **** poor design.

I've been looking at contactless sensors such as the Murata LP05M4R1AA but none of them so far can stand more than 60°C. I just need to find a potentiometer, I can print a mount easily in a high temperature plastic like PETG. An alternative is to intercept the signal and clean it up electronically but again the environment it needs to live in is the challenge.

I believe the resistance of the potentiometer needs to be 4.2k ohm since thats what both of my current sensors are.

 

A follow up - engineering = poor.

So I 've completely stripped one of the the capstans and there is no bearing whatsoever on the capstan itself, the capstan relies totally on a centre spindle fixed with two set screws to stop it rocking around - the same centre spindle that drives the pot. If this were done correctly the capstan would have its own bearings, the spindle should not do anything other than transfer rotational information.

As it stands if the centre bushing on the capstan wears or corrodes (see grounds and electrical paths why) the spindle gets loose and sloppy, if you also consider that it isn't lubricated either and there is no lubrication point for it then the results are pretty much guaranteed.

Now need to sink a few whilst I figure out a more robust solution - I wonder how many position sensors have been consigned to the trash because of this.

You can see how much the capstan can move without the spindle inserted, you can also see what appears to be a sleeve bushing that should be replaceable - not sure I'll go this route as I lack the facilities.

 

Mmmmm,

I reckon they did a damn good job, given the era of things.

The car got out of the warranty period witoiut too many issues. That is what ANY manufacturer wanted/wants, the rest in not their issue.

These are still rocketing around at 35+++ years, and YES, there will be things that need attention, and if one really wants to, re-invented.
My 1963 MK X, has MANY things I could upgrade, but, hell, it goes up and down the highway without fuss, and has never let me down. Starts when I want it, stops when I turn the key off, job done.

None of mine were an issue after a TPS change, lube that shaft, and moved on.

The PreHE, same basic thing, with a MONGREL TPS set up, and 1976, is now at 652000kms, and thats Aussie HARD kms, and still fine. I worry not.

 

Given the era this 'ECU' thing was kind of new to everyone, they were all in learning mode - evidenced by the change to this setup in late models (6 litre).

It is all about the sensitivity of the ECU to this value, and this information I simply don't have - just how critical is a few hundredths of a volt just how does the ECU use this voltage (other than injector pulse width) and how sensitive is it - given that this car was running 6 weeks ago ... until I started your list

 

Ben,

The split is 0.32 5o 0.36, you have that.

Sensitivity, no idea.

At about 0.45 the fuel cut off based on vac kicks in.

I know of HE's where the TPS is at 0.30ish, and the car is happy, as is the owner.

All I know, is mine were at 0.34 consistent, and that was the magic number, and thats all I have to go on.

The later TPS is much smaller, so I "suspect", and thats all it is, they are a Hall Sensor style, which makes perfect sense. Then the spring return to zero was a quantum leap compared to the old Bourns units.

They went "Hall" with version 2 of the D Jetronic trigger board in the early 8-0's, and that was a whole new world for us PreHE owners, but I digress.

 

Not in the least critical, Ben. You are worrying quite unnecessarily about his minor variance. Please do not think I blame you for this, we all have things we get stuck on getting more perfect than needed! I am just saying no need to worry unless you want to!

 

Another data point, I have the red spring loaded TPS and it is a pain to set. I had two slotted screws to hold it down. Every time I had it set, when I would finish tightening the screws it would move the TPS. Or if I cycled the throttle of would return out of spec. I moved to 12mm long Allen screws with a star washer under the TPS and lock washer under the screw head. That seemed to help get it locked accurate and consistent.

 

Appreciated Greg. This just triggered the OCD - a spec is a spec right - the combination of being an engineer and having OCD can be a pain in the butt sometimes.

I may have a resolution - watch this space ....

 

My current V12 has a lot of wear throughout the entire linkage system which adds a bit of frustration in getting the adjustments just right. I keep waiting for someone to engineer a nice fix-it package and sell it to willing buyers....like me

Now.....

Poor engineering? Or engineering down to an acceptable life span and manufacturing cost?

I'm working on an Ferrari V12 and all linkages (throttle, brake, clutch) are very robust, have Heim joints and roller bearings, and the like. I've attached a picture of the throttle linkage....which is really delicious:



Lovely, isn't it?

But, but, but.......

Remember......there's a reason that Jaguars are half the price of a Ferrari

Thirty years from now that throttle linkage will still be smooth as a baby's bottom, and still precise enough to bring a smile of content to an engineer's face . The car itself may well be rusted away and reduced to a pile of brown dust. But the not the throttle linkage !

Cheers
DD