Yeah, unlikely, I agree


All 12 professionally serviced before installation by Dave Faircloth:
Jaguar Fuel Injector Service

As an aside I'll mention that this is the smoothest idling V12 I've ever experienced....when it was in the donor car and running, that is . Dave called to mention they were "the most evenly balanced set of 12 that he has ever seen".


Will do.

Cheers
DD

 

Doug, been MIA for a few days.

That TPS not firing the injectors when blipped with Ign ON is a no no.

Same scenario as having the TPS unplugged.

Everything else I have caught up with makes perfect sense, and it should run.

I reckon you have covered this, but is the ATS and CTS plugged to the correct sensor???.

 

I might be narrowing in on something.

Before explaining what I think I've found, a quick question.......

Pin 19 of the ECU is labeled "throttle pot ground signal" . I'm confused by the word 'signal' in this case. It makes it sound like an *input* to the ECU. Is it?

I thought the ECU simply *provided* the ground for the TPS and the 'signal" (the info actually used by the ECU) was on Pin 7, "Throttle pot wiper".

The CTS shares the shame yellow/black wire to Pin 19, by the way.

Tomorrow will retrace my steps but here's what I'm getting:

Thinking the ECU *provides* a ground I unplugged the TPS checked the resistance of yellow/black wire to ground. With the key off I have .5 ohm. With the key on I have 300 ohms.

How do I interpret this?

This is with the CTS plugged in, by the way. Tomorrow I will unplug the CTS and see if anything changes.

Am I on to something here?

Cheers
DD

 

The 1994 diagrams list more info in relation to values so long as we remember what modules were different. The wire you mention (although different pin on ECU) is listed as OUTPUT and both active and inactive value is ground.

 

Doug,

This is a schematics I have used for years to trace out wires on engine fire cars.

V12 EFI schematics Australian cars.pdf

That pin #19 is CTS and TPS related, and Yellow/Black.

Not sure if I sent it to you earlier??

 

Right, thanks.

I understand that it is related to both the TPS and CTS. I'm confused by the resistance readings I'm getting. And I'm not sure if the yellow/black wire is supposed to simply provide a ground for the TPS and CTS or not.

I'll do more checking and mulling today with a clearer head

Cheers
DD

 

I've done some research. Our Jag TPS and CTS grounding method is shared by other cars. It appears that the ECU provides a 'conditioned ground' to the TPS and the CTS. This is a 'noise filtering' tactic to give clearer signals, a fairly common arrangement older FI systems.

Interestingly, the Series III XJ6 is an exception (surely there are others) ...using a direct chassis ground

Anyhow.....

Many report simply running a new ground to the TPS and CTS and everything came back to life with no (apparent) ill results.

I'll abandon the existing wire and ground the two sensors independently of the ECU and see what happens.

Cheers
DD

 

The XJ6 isn't a true TPS, it's a throttle closed and WOT switch rolled into one.

 

Sorry, I was referring to the Series III CTS...but forgot to say so. Yes, correct, the old XJ6 has a throttle 'switch' as you say.

What do you think of my plan?



Cheers
DD

 

Doug
I have been following this with interest, and have no ideas; but I think a recap of all the things you have done (assuming your ground idea does not spring the car into life) would be a good plan, as when I get to this stage, I often find I lose track of the assumptions I have made!
Just a few points to guide us/refresh us all, (and please ignore this post if it does not help):
Are you 100% certain it is a fuelling issue, and how?
Are you 100% certain there is a spark to the plugs, and how?
If you think the ECU pin 19 is the problem, or even a possibility of another sort of ECU problem, is there another known-good ECU you can swap in to check it?
If the ground from the TPS and the CTS is iffy, have you continuity tested the wire to the ECU plug?
Is the CTS sensor definitely good?


Cheers
Greg

 

Doug, I had a look at that YB wire on my TPS today, on my car it has 5R to chassis ground, its not a ground. It provides a calibrated reference so the ECU can determine TPS and CTS values. My guess would be a 5 volt reference, my car is not running ATM so I can not measure it, some other diligent chap might be able to do this for you.

If you measure resistance from YB to chassis ground you will get a high resistance and it will drop to about 4-5R, this is because there is a capacitor being charged., which in my mind confirms this is the output of a regulator.

 

If I squirt fuel into the intake manifolds it starts instantly (and actually sounds great!) for a few seconds. So, I know I have spark and know that I am lacking fuel.

Confusing part:

Injector noid light blinks when cranking engine yet there is no injector life when opening the throttle

A used ECU is what got me this far. Originally, I had no noid light blinking at all, period. I have another used ECU but it is in such bad shape I'm a little afraid to plug it in


Yes and yes

What I still haven't done, but will do, is check fuel pressure. I got side-tracked on the TPS grounding thing.

However, lack of fuel pressure would not explain why the injectors don't operate when I snap the throttle.


Thanks for chiming in !

Cheers
DD

 

Where does the TPS (and CTS) get a ground from, then?




I'm not sure what you mean by "5R"

On mine the YB wire has .5 ohm resistance to ground with the key off and 300 ohms resistance to ground with the key on. I dunno why.

On mine reference voltage (5 volt) is supplied on the yellow/pink wire and the yellow/white is the 'wiper signal' which is what (I thought) the ECU actually used to help determine fueling

Cheers and thanks
DD

 

Doug, Why not pull out one of the front injectors and see if it is actually spraying, and while someone blips the throttle, see if you can feel it shake?
I agree that checking fuel pressure is an important thing to do, before wondering about more exotic causes1 I chased a funny no-start for ages earlier this year before a new B bank FPR cured all the various symptoms.
Greg

 

As a general rule, all sensors are grounded together so there can be no voltage difference between them. Makes for "truer" readings to the ECU.

I'll have to spend some quality time with the wiring diagram to see if there is anything else that jumps out at me.

Might be worth plugging in that extra ECU just to see what happens. Can't hurt anything.

Cheers,
Craig

 

If you put a screwdriver to your ear and on the injector, can you hear them clicking? Just wondering if they are getting power to the noid light, but not working? Grasping at straws, I know, but worth verifying that the injectors are functioning mechanically.

 

Sorry Doug I should have explained my self better. I wrote my reply in haste….. And sometimes I don't translate my experience fixing electronics to laymans terms.

The reason you are getting these resistance measurements is because you are measuring to ground through an electrical component, when I measured mine it acted like a capacitor. The trap in measuring resistance without BOTH ends of the cable disconnected is - you could be measuring some component in another circuit.

So forget the resistance measurements of the TPS and CTS in circuit to the ECU or chassis ground these will just confuse the situation.

These sensors are NOT grounded this would cause issues with the reference voltage. The ECU provides the sensors a Voltage referenced to ECU ground (battery neg) to ensure the voltage does not vary with RPM and other drains on the system. See diagram - the sensors will be isolated by being connected across the reference.

The sensor common (or signal ground) and chassis ground is not connected to isolate the sensor lines from noise. There is not enough detail in the circuit to make a call on this, but measurements on my TPS make me pretty sure about this.

If you want to check continuity of a component in a circuit the component should be removed to avoid other components influencing the resistance measurement. So I avoid this unless Im looking for a short or open circuit.

Can you check the voltage on each pin of the TPS and POST THESE VALUES. With the wiper can you take 3 measurements 1 at each end and 1 in the middle.

Lastly can you please post a dot point update as reading through all the posts its easy to miss some vital info.

 

Turns out yours was a very good grasp !

I rigged up a jumper wire to the starter relay, turned the key 'on', donned my mechanic's stethoscope, cranked the engine and....and....and.....

None of the injectors are clicking. Gah !

Got on the phone with David Faircloth Jaguar Fuel Injector Service (great guy) and he's nearly positive the injectors are simply stuck from having been stored in the trunk of the car for so long. I never woulda thunk it but apparently it's a common-ish scenario.

Either that or I somehow managed to smoke all twelve of 'em via some sort of wiring foul-up related to the engine swap. ! I checked six and all of those were at 2.7-2.9 ohms resistance....which I think is correct...so maybe I got lucky. Not sure what other electrical check I can perform.

I feel like a dumbass! I fell into the trap of assuming I had a high-tech problem when it appears, and hopefully will prove to be, a low-tech problem.

I'll let everyone know how things progress.

Cheers and thanks
DD

 

A reasonably simple fix if that's all it is.

 

1.5V battery across the injector pins will fire the injector, don't leave them energised long.

12 stuck injectors who would have looked for that...............