On later model cars there is a sensor reference that is five volts. The five volts comes from the onboard computer. This voltage is used for sensors in liew of the battery voltage which can vary because of the alternator output. Was the XJS pre five volts and if it was post five volts where is the five volt shown on the electrical diagrams?

 

First mention i can find of such is in the '92 xjs electrical pdf diagram input/output listings. Some of these would also apply to '89 on for digital ignition etc. and possibly even earlier for fuel injection but the diagrams prior to '92 don't include the input/outputs and active/inactive readings.

 

All my D Jetronic cars (PreHE} had 5v reference for the CTS & ATS.I dont remember what the feed to the TPS was, so lets call that a CRAFT moment.

The P Digital, (HE) had 5v reference for the CTS, ATS and TPS.

Came from respective "pins" of teh ECU.

 

Thanks for your reply's, This internet posting http://www.pearsoned.ca/highered/div...toTec_ch25.pdf raised my curiosity about five volt reference voltages as it applies to sensors and their interaction with the ECU.(See Page 525) A faulty five volts could as you Blokes say " Drive you up the wall;" since the five vaults regulates and reports the sensor info to the ECU.
I don't have sufficient information on Jaguar's introduction of computer controls on any of the XJS models. I have a 1993 6cyl XJS and also the Electric Manual for that year, but could find no info on reference voltages. That papacy of information made me wonder if Jag had a different system

 

"Up the wall", standard living area for a V12 owner.

The 5v is TO the sensor, the return wire is the signal TO the ECU, to "inform" it of whatever it needs from that sensor. to do what it does (WE HOPE) Gets messy sometimes.

Loss, or drop, of that 5v reeks havoc.

 

On the 6CU and 16CU it is pin 20

 

jamesholland
Pease clarify: On the 6CU and 16CU

 

Pre facelift V12s used an ECU that is different from the later cars which used a 36 CU. On the pre facelift V12 ECUs pin 20 carries the reference 5v voltage.

 

I can't find a 36pin ECU on my 1993 Electrical Manual. Looked at Chapter 25, but no luck.

 

I doubt it has any reference to the pins.

3CU, D Jetronic, had more than 3 pins..Schematics somewhere, but not needed.

6CU, Early He, had more than 6 pins. 22 in fact.

16CU, later HE, had more than 16 pins. 22 also.

36CU, same size physically from memory?, so probably 22 pins also.

It is a "Model ID code" as best I know.

 

What does the abbreviation "CU stand for? I thought it was a short cut for ECU

 

Um, dunno,

As a pure wild stab in the dark, CU could be "Control Unit", and the numbers the generation of same as they improve (haha) and alter things, a new number creeps in.

All I do know is the 16 was more stable than the 6, and also processed the data 5? times faster than the 6. All the 6 units I have replaced with the 16 (plig and play) did improve the engine, and it was noticeable to the human ear, not any machines, which I dont have.

Never thought about until now, and its gone already, oops.

 

Its pin 20 on a 36CU as well:
LUCAS EFI / AJ6 Engineering

 

James,
Great dissertation on CU's (CU meaning Control Unit). Since I have a 6cyl and 1993 XJS my question was not ,as far as I can see, answered. I was only looking for the 5 vt output from the ECU to the sensors. I was not sure if Jaguar had used 5 VT? Any help on that question???

 

On the V12 CU16 all the sensors and TPS run on 5v.

 

I reckon answer #3 in here does answer that. TPS, CTS, ATS.

Also #12, = Control Unit.

#13, Pin 20 is also a 5V reference.

Or am I missing something??