You get anywhere with the TPS ?

 

@ BebKenobi: Not yet. Had to go take care of a overheating problem on my granddaughter's car. Will tackle the TPS tomorrow.

 

TPS Tests:
Test 1: TPS harness loom. Key "ON" Closed Throttle.
Yellow/Black from Pin 19 at ECU = 0.01v. This goes to the Yellow wire of the TPS pigtail.
Yellow/Pink from Pin 20 at ECU = 4.88v. This goes to Green wire of the TPS pigtail.
Yellow/White from Pin 7 at ECU = 3.45v. This goes to the Red wire of the TPS pigtail. This is the TPS wiper signal.

Test 2. TPS connected to Loom; Key "ON" Closed Throttle.
Green wire: 4.88v
Red Wire: 4.14 v
Yellow wire: 0.01 v

Test 3. TPS connected. Key "ON"
Red and Yellow wire backprobed to DVOM
Throttle closed = 4.17v
Throttle WOT = 4.80 v.
Something is wrong here or I am going nuts.
1. The TPS wiper signal as per the specs should be 0.32 -0.34 v and that signal goes back to the ECU.
2. With the Key "ON" the ECU is sending 3.45v to the TPS via the yellow/white wire.
3. I should not have voltage on the Yellow/White wire that comes from the ECU. Am I correct?
4. With the throttle closed. I have 4.88v on the green wire. That's OK. On the red wire I have 4.14v. It does not change with throttle position.

Test 4. TPS Resistance check. I can only get a reading on the 200m scale.
Closed throttle = .329 ohms with a very smooth transition to.....
WOT = . 28 ohms.

My opinion: New TPS and Faulty ECU.
What do you all think?

 

Sanchez
You wrote:
3. I should not have voltage on the Yellow/White wire that comes from the ECU. Am I correct?
YES, the yellow/white should only carry the wiper signal back to the ECU. Clearly something wrong! (statement of the obvious) I am a bit confused by some of your post, as you sometimes talk about the loom colours and sometimes the TPS colours. So I set out below the loom colours/TPS colours on my car:

The loom to TPS colours are (I have the later red TPS on my car) as shown below. BUT, if you have the earlier black plastic Bournes TPS, maybe the TPS wire colours (not the loom wire colours) are different and your connections are correct. I am just posting this for info for you to check.

Loom yellow/pink goes to TPS RED = 5v volts constant ignition on
Loom yellow/white goes to TPS GREEN = signal to ECU from the wiper. It should be 0.32v throttle closed ignition on
Loom Yellow/black goes to TPS BLACK
Quite often the loom colours are very faded so be 100% sure you have the right ones. From your post, I think you have correctly identified the loom colours, but make 100% sure those loom colours are going to the TPS ones they should be going to.
As you are showing 3.5 volts on the wiper signal yellow/white wire (even with the TPS disconnected from the loom) this is a short of some sort, I would suspect a loom short from a constant 5 v wire to the other one, and would eliminate this possibility before worried about the ECU. I would test that yellow/white wire for continuity. You can always run a test wire straight over the roof from the TPS wiper to the ECU and eliminate it completely if needed and see if that chnages the voltage, if it does loom short is proven.
You are closing in on the problem, that is for sure, if that is any comfort...

 

Does this depend on whether the TPS has been updated to the later TPS - I have a set of colours listed that don't include black on the TPS, I have two TPS's and both are the same, my mounted TPS is currently on the desk and there is no black wire, my colours are the same as those listed by Sanchez - I'm going to power it up via a bench PSU and confirm function lines.

These are my colours and they aren't what you would expect - I need now to confirm the car colours - this will need to happen tomorrow as it is too dark and miserable outside, the wires are also still filthy I need to clean them off.
TPS Yellow is connected to Yellow/Pink = +VE
TPS Red is connected to Yellow/White = Signal
TPS Green is connected to Yellow/Black = -VE

This image shows mine on the bench (ignore my mods) - the dark blue cable is -ve, yellow is +ve - yes mine is over volts a bit at rest.





The potentiometer kit does list this which concurs with Greg's - this is a later TPS I think and is Red, not a large black thing
Red Yellow/Pink 5 volts
Green Yellow/White Signal out
Black Yellow/Black 0 volts

If you have 3.45 volts at rest that is completely off - should be no more than 0.2. Have you had this TPS off ? - it sounds to me like it got put on 120 out of place - the problem with these though is that if you overrotate them they're toast, they have stops internally so the shafts break and the only way to know is to tear down - this can also break them - ask me how I know.

 

How many pins does the car harness have that is plugged into your TPS ?? - it should have three and a blanked portion - I ask because I don't see any white on mine at all ... although the light is rubbish ... and now I can't recall where I got my notes from but the pins / TPS colours and what they represent is accurate.

I'm 99.9% sure this is my TPS connector, there is another nearby but it has 4 pins but potentially would fit - either way I'll verify in daylight.

 

I just doublechecked the loom wiring:
At the loom plug there are:
2 Y/K wires
2 Y/B wires
1 Y/W wire.

Y/K connect to green wire of TPS pigtail.
Y/B connect to yellow wire of TPS pigtail.
Y/W connect to red wire on TPS pigtail.
The plug from the Loom can only connect to the pigtail of the TPS one way. I have the colors correct.
See attached photo
My TPS is the Bournes brand. (Red, Yellow, Green)
@ BenKenobi: It is a 3 pin plug.
As stated above the 2 Y/K wires go to a pin on the plug; the 2 Y/B wires go to another pin on the plug and the single Y/W wire goes to the 3rd pin. Take a look at the photo below.

 

And here lies the conundrum - if you put yellow to ground and green to +ve the my TPS works backwards from 5 volts down - just tried it .... - either way your signal should be circa 0.2 some volts throttle closed.

Time to retire - had my damn meter in the wrong side .... colours confirmed Yellow on the Bourne (Black) pot IS -VE, Green is +VE and Red is the Signal.

 

I just completed a test on the Y/W wire from the engine bay to the trunk of car. TEST DONE WITH TPS DISCONNECTED FROM LOOM
The wire is not shorted to power anywhere.
I ran a wire over the top of the car from Pin 7 of the ECU harness and the Y/W wire had continuity. No shorts anywhere.
I peeled back the insulation on the Y/W wire at the ECU plug and this is what I saw.
The color does not show up well in the photo but it is the Y/W wire.

With the Y/W wire complete I still had the voltage shown.
Next I cut the Y/W wire and connected the DVOM to the part of the wire going to the ECU and this is what I saw

Voltage reading from ECU on the cut Y/W wire


DVOM connected to cut Y/W wire going to the ECU

Since the voltage is coming from the ECU I believe I have a problem at the ECU. Should I open the ECU to see?
From the trunk to the front of the car the Y/W wire has continuity.

 

Sanchez
I cannot help you on the ECU, but it certainly looks like a fault. Is your ECU a 6CU or a 16CU?

 

Greg, It is a 6CU. I am looking for a 16CU replacement. The ones I find are of unknown condition with the cheapest around $299 + shipping, and up to $900 again unknown condition.
I am in email contact with AJ6 Engineering, but Roger informed me that he is just back from a serious heart attack and his backlog is enormous and he is very, very slowly getting back up to speed which as he said " maybe never".
A member of this forum is sending me a loaner ECU, again unknown condition for me to swap out with mine. If his works, I will then bite the bullet and get my own. I do not know whether his is a 6CU or a 16CU.
I wish I could get one from a known working car.
Any connections on your side of the pond for a working ECU?

 

I have a brand spanking new 6CU in it's box (bought on impulse at an auction - didn't expect to win) but I'd be pushing you into 16CU if you're stuck replacing, Roger knows his stuff but that means he is globally in demand, he also told me he would be months getting to me when I asked about an exhaust and ECU upgrade.

Let's see what happens with the loaner.

 

@ Ben: I will surely take you up on that offer if the ECU is for The Lucas system. Whether it is a 16 CU (DAC4585; DAC6335; DAC4118) or a 6CU (DAC 3586). It would not matter to me.
Roger Bywater told me that the 16CU for the Marelli system will not work properly with the Lucas system. The above 16CU numbers are the ones Roger recommended.

 

Has no DAC number on it but I did research it (Jaguar XJS XJ12 V12 81-86 5.3 engine 6CU ECU 83705B DAC3062 LRZ115), I'm not 100% sure which chassis numbers of Jaguar XJS 5.3 it is intended for but it sure comes uip for the XJS 5.3, it is a Lucas reman unit, I've opened the box just - the security seal is intact on the bag that it is in, if it turns out you do need it we can work something out - don't want to be breaking any rules here ...

 

Ben, Sanchez,

I dont want to scuttle anything, but.

That DAC3062 that Ben has is for None Cat cars.

The DAC3056 is a Cat system ECU.

I thought I posted this chart, maybe had a brain fart.

Here it is.

A Cat spec ECU can be used in None Cat cars, as there are NO wires in the plug for sensors etc. I have done this, no issues. BUT, a None Cat ECU in a Cat spec car, nope I reckon, but I am NOT an expert here.

Marelli 16CU, agreed, they be different and stay with the Marelli spec cars.

 

Not scuttling anything Grant, the variations across the regions even for cars of the same model year make accurate identification more than challenging. I bought this purely on a whim and by chance (silly price wins auction go figure - I had no competition) and I figured new in box would be worthwhile for some Jag owner one day. It is back in its corner with all my other NOS car spares.

 

Hell yes Ben.

Parts are getting harder and harder for these by the day, so private stash piles are the New Parts Stores.

 

I am not at all convinced that your ecu is bad. I really do not know what voltage Jag intended be on the signal wire, but based on my experienced with other brands, your voltage readings might be normal. I would expect to have 5v reference on red, ground on yellow, and signal on green. If you jumper all 3 together, the ground should pull down the voltage on the signal to near 0v, say less than 0.5v. If it does not, I would be looking for a poor connection on the TPS ground circuit, or possibly the ECU ground. If jumpering all 3 wires together does bring the green signal circuit below 0.5v, replace the TPS and see what happens. I really doubt the ECU is the problem.

 

I think you may be mistaken about this point. I understand the situation to be as follows:
Sanchez is getting 3.5 volts continuously OUT of the ECU pin (with the TPS unplugged from the loom) that is meant to RECEIVE only the signal from the TPS, and should have 0 volts, TPS unplugged.

 

Sanchez,

Much thought on this today.
Went digging in my shed for my hand written notes from way back.

From my hand written notes:

YB = ECU #19 = Yellow of TPS. A splice off (at the loom plug) to one side of the CTS. Other side of CTS is UC = #5 of ECU.
YK = ECU # 20 = Green of TPS. A splice off (at the loom plug) to one side of the ATS. Other side of ATS is RU = #21 of ECU
YW = ECU #7 = Red of TPS.
Matches your notes also.

My understanding from years ago:

The YW, UC, RU are all 5V reference from the ECU.
The YB and YK, with the splices from ATS and CTS, are the return to the ECU. Bringing the TPS signal with them for load etc. And that is a pure guess, as ECU operation is not one of my traits.

That odd voltage in those wires could be a sort in the looms to the ATS and the CTS, rather common on the CTS, not so much the ATS.
OR
The ATS and the CTS are cross connected, that is common, pigtails and plugs are identical, and near enough the same length to confuse, and reeks all sorts of odd shiiit, and NO Injector pulse.

Those TPS readings are not good, and very suspect, maybe even a short inside, BUT, that does not answer the oddities with the TPS unplugged.