***VERDICT IS IN!****

at idle across the red and yellow the TPS produces 0.5v at idle and steadily increases to 1.0V at 15% throttle before dropping to 0.3v for the remaining 85% of the throttle travel.

now wheres the cheapest place to get one of these bad boys? MISH!!!!!!!

 

On an 85 car the gearbox is not controlled by the ECU and shift points are entirely controlled mechanically by the box itself and the vacuum signal to it from the A bank manifold.

If the TPS is missing wires etc, it would, I feel, be best to replace it. It sends to the ECU a signal which tells it how far open the throttles are, and therefore what fuelling is required to the injectors. It should be set with a voltmeter to 0.32V at thottled closed (ignition on engine off to set it).

Greg

 

Great stuff, looks like this will do it! Your post arrived about 5 seconds after I posted. Bought my new one from Rockauto.

Greg

 

i was just looking at rockauto. theyve got it for $119. can anyone say EXPRESS SHIPPING! WOO!.

 

crap Rockauto is sold out. part # EAC9634 is what they listed. Jagbits.com lists it as a 89-94 compatability only.

anyone know what part# i need?

 

That's probably the later style "red" TPS. It can be used on your car but you'll need the little adapter kit. You can do some Googling and/or call some Jag specialists for that.

You car orginally had the black "Bournes" TPS which Jaguar discontinued a few years ago. I think you might find an aftermarket duplicate if you call around....but in my experience the quality is iffy on these.

With a little bit of fiddling...2 or 3 hours maybe....you can use a $25 Mustang TPS. I posted some info on this a few months ago. Do a quick archive search. I had great luck with the Mustang TPS but experiences vary.

Cheers
DD

 

Sorry, forgot to mention that the exact part is NLA and unobtainable anywhere AFAIK. The red Rockauto one is the one I used. As Doug said it needs a bit of fettling to fit. Either a kit can be bought, which consists of a spacer plate and an adapter to fit the axle of the TPS to the capstan spindle (quite expensive 140 UKP), or you can make one up.

What I did was to take a square plate of aluminium about 1/4 inch thick and drill a hole for the TPS axle, and drilled holes to mount it to the capstan using the three threaded holes in the capstan that used to hold the old TPS to it.

Then into the plate drill and tap two extra holes to take screws to locate the new TPS adjustment lugs. On the capstan itelf, undo the spindle that the TPS axle is operated by (undo the two screws in the top of the capstan and out it lifts). This spindle is too long for the new TPS and also has the wrong end on it to fit over, and thus actuate, the new TPS axle. I bravely measured and cut the capstan spindle to the correct length (allowing for the overlap of the TPS and the spindle), then cut a vertical slot in the spindle end which fits over the blade-type end of the new TPS axle. Job done. Works fine.

 

Wow, i love a good Fab only repair.

 

Doug, do you remember the name of the thread. search came up with squat and i went back 8 pages and couldnt find anything.

 

Try this

https://www.jaguarforums.com/forum/x...or-best-32774/

 

Advance Auto has 2 different ones. one for $20 and one for $36. they cant figure out what the difference is. both are BWD. AC delco wants $50.

 

Rock Auto $25.79 for the AC Delco part

Shoot, just go to your local neighborhood parts store. As I recall this part number works on *many* different Fords. Should be easy to find locally.

Cheers
DD

 

i ended up getting a BWD. the difference ended up being the thickness of the barrel that the rotating shaft sits inside of.

 

Alright, i figured out the wiring. Red is the wiper, Green is the high resistance side, and yellow is low resistance.

so heres some bullshit. from red to green i read .27v and it steadily decreases to about .08v.
from red to yellow i get 0v at idle and up to .28v at WOT. WTF?!? im not even breaking the .5 volt mark, let alone 4.5v
before i started this project i was reading half a volt at idle and now im reading nothing.

TPS across red and yellow reads between .55k ohms at idle and 3.12k ohm at WOT. across red and green it reads 3.8k ohm at idle and .7k ohm at WOT.

yellow and green reads 3.9k ohms at all positions. typical potentiaometer function.

i got some sparks and arcs from a few wires in the engine bay while trying to get it wired up. could i have blow a fuse or something? what volts is the Red and Yellow on the chassis harness supposed to read without the TPS plugged in? it should be at least 5 volts right?

i had to have blown something. relay, fuse, something.


i dont understand how i started with .5v at idle and ended with jack at idle.

 

there doesnt appear to be any fuse or relay in the wiring schematic. could it simply be bad wires?

 

the car runs much worse at idle and all through the RPM band with the new sensor installed. this is clearly due to the lack of voltage.

 

Heres what im thinking. i remember the TPS making a tick sound when i first hooked it up and was test fitting everything, and also when i was getting some sparks from some shorted bare wires.

the TPS no longer makes this noise when connected. i remember one of the wires that was getting shorted was to the ignition coil. the ECU appears to be getting Earth from the ignition coil. so either i fried the ignition coil and the ECU isnt getting Earth, or i fried the ECU and its not doing a damn thing.

also, when i first got the car i could unplug the vacuum line to the ECU and the idle would slow down and it would settle out a bit and it wouldnt bog out when the throttle was opened. plugging it back in caused the idle to accelerate and the engine to bog.

after my short circiut, plugging the ECU back in DOES NOT effect the idle in any way. it will however still bog. so something in the ECU has changed. i must have damaged it.

 

Alright, i figured out the wiring. Red is the wiper, Green is the high resistance side, and yellow is low resistance.

so heres some bullshit. from red to green i read .27v and it steadily decreases to about .08v.
from red to yellow i get 0v at idle and up to .28v at WOT. WTF?!? im not even breaking the .5 volt mark, let alone 4.5v
before i started this project i was reading half a volt at idle and now im reading nothing.

TPS across red and yellow reads between .55k ohms at idle and 3.12k ohm at WOT. across red and green it reads 3.8k ohm at idle and .7k ohm at WOT.

yellow and green reads 3.9k ohms at all positions. typical potentiaometer function.

i got some sparks and arcs from a few wires in the engine bay while trying to get it wired up. could i have blow a fuse or something? what volts is the Red and Yellow on the chassis harness supposed to read without the TPS plugged in? it should be at least 5 volts right?

i had to have blown something. relay, fuse, something.


i dont understand how i started with .5v at idle and ended with jack at idle.

 

Wow, lots of posts since I was last on!
Unfortunately I don't have my notes here at work, so I'm not going to be much help. I switched mine over to the Ford TPS, but have not been able to figure out which wire goes where with any certainty. The Ford TPS is labeled A, B and C, and the wires from the old Jag TPS were Red, Yellow and Green.
I think (and I hope someone can confirm this for both of us) A=Red, B=Yellow and C=Green
If anyone can confirm this I'm sure both of us would be grateful!

 

how long has yours been switched? have you had it running since? the Red is the pot brush, the green is the high resistance side, and the yellow is the low resistance side.... apparently.

A = Yellow
B = Red
C = Green

when i first wired it up i just started switching them around trying to get a good reading and i think i fried the TPS by doing this. it would tick the first few times i plugged it in and now it wont tick at all. im pretty sure its more than simply a mechanical potentiometer. im hoping that all i did was crosswire the TPS and ruin it. ill be swapping it out for a different one tomorrow and hoping for the best.