2) AAV, rear of the B cylinder head. Is it closing 100% when at operating temp. If it does NOT close as designed, the ECU WILL cut fuel, turn it ON again, off again, etc etc. See this attachment I have included.

Grant, how does the ECU know to cut the fuel if the AAV is not fully closed? Is there a flow meter somewhere?

CHeers
Craig

 

The ECU compares revs with the TPS position. If the TPS is closed and revs are higher than 1400, it cuts the fuel; this is a fuel saving on the over-run feature, such as when on a trailing throttle when slowing down.

 

Craig,

Nope, not that clever.

As Greg has explained.

If that AAV does not close at a predetermined temperature, then the incoming "extra" air raises the revs, the ECU knows the TPS is at idle, and decides that fuel is not needed. Then the revs drop, the planets realign, fuel back ON, and then off as the specs dont match.

Same thing if the TPS has dead spots, the ECU cannot cope with "fuzzy" anything. Its either on song, or its off. The CTS, being a PRIME fueling meter is a classic on the V12.

Example, running V12, unplug the CTS, DEAD V12, simple as that.

 

A bit strange as I tried unplugging the CTS on the front LH bank next to the Thermostat housing and she didn't die. (No paperclip inserted)
Is it meant to stop the engine when unplugged?

I still reckon its the TPS as I also tried the CTS with the paperclip inserted and it still stalled a couple of times.





Cheers
Craig

 

On a Lucas car, it will die immediately. If it does not, then I suspect a loom fault (in effect the paperclip, but made by short between the wires). If Grant agrees with this, then carefully peeling back the loom cover from the plug backwards might find it. Could even be dirt or a fault in the actual plug making a circuit, so worth cleaning that first.

 

Agreed.

If the Lucas, Pre 1989 V12, continues to run with the CTS unplugged and NOT bridged, there is a loom issue.

The 2 wires of that CTS travel aft, and pick up the ATS (Air Temp Sensor) on the way, then splice into wires AT the TPS, chassis side of the loom.

Any number of these could be cross feeding, and keeping that thing running.

This is Pin out I charted a very long time ago, and is priceless when diagnosing a strange V12 behaviour.

 

Grant, the info and experience you have is legendary!

Cheers
Craig

 

Greg, thank you also, very valuable info. Now I have some more work to do.

 

So... If the CTS was bridged back in the loom somewhere, what is the worst it can do?

Have issues whiles cold?
Be uneconomical while cold?

Update: Tested the CTS again and realized I replaced it 3 months ago along with other stuff. Just pulled the plug again today and yes it killed the engine. (Cant of done it right last time)

The AAV was replaced 3 months ago also so not that.

The TPS should hopefully do it.

Thanks again

Craig

 

So after all of this I will have renewed the following.

CTS
Fuel Pump
Fuel filters
Fuel lines on rails
AAV
Spark Plugs
TPS
Dizzy cap
AIr filters


The only thing left is the ATS???
How critical is the ATS sensor and what does it do?

Cheers
Craig

 

Coming in late on this thread so may have missed a few things

Years ago I had a serious cutting-out problem on my '88 XJS Lucas car. Only under load. Almost like the key was being turned on-off very rapidly.

Cutting to the end of the chase......

It was the inlet-side fuel pressure regulator.

The inlet side regulator can be easily bypassed to take it out of the picture...temporarily or permanently

Cheers
DD

 

Hi Doug, Did it completely cut all 12 pots?

 

It's just a fueling 'trimmer'. The most it can do is richen the mixture by 8% or something like that. I think your problem is too severe for the ATS to cause. I once inadvertently left mine unplugged and never knew it. I just noticed the connector flopping in the breeze one day. Lord knows how long it had been left disconnected.

However.....

Mixing up the ATS connector with the CTS connector...well....that would be a horse of a different color. Might be worth checking just for the heck of it.

Cheers
DD

 

I never counted

But it was a severe bucking/cutting out. And a pressure regulator problem should effect all cylinders equally, I'd think.

Cheers
DD

 

Cracker
I am a little lost now, but can we recap a bit? Which if the below are true/have you already done?
I understand that the car is momentarily cutting out when warm and under load?
You are about to fit a new TPS - (which is vital to do)?
As Doug said, getting rid of the A bank FPR is a good plan, or at the least renew it. It is NOT the same pressure rating as the B bank one, so be careful you get the right one from a specialist supplier.
I think I am correct in saying you have not renewed the Amplifier (sited at the rear top of the B bank manifold)? If I am right, I would do this as it might well be the trouble. FWIW, a new amp fixed all sorts of odd no-start symptoms on my car. I brace myself for grief from unbelievers - but I have had NO success just changing the internal module on any of my amplifiers. A new one from David Manners did the trick perfectly.
Also carefully check the two wires that go from the bottom of the dizzy to the amplifier. If one of these is fractured or iffy, it can produce cut outs. You may have to get the star wheel off the spindle to properly check that there is no wire problem inside the dizzy bottom, as well. These wires send the signal (which is created by the star wheel/magnet pickup system) to the amp to time the spark. It is just possible that under load when the sprung plate at the bottom of the dizzy moves under rotational or vacuum capsule forces, that something is shorting out.
Also, the coils may be giving up when under load, as this requires it/them (if you still have the twin coils) to do more.
Finally, if you rev the car in neutral, does it cut out?
Greg

 

See above
Amplifier = no

Finally, if you rev the car in neutral, does it cut out? NO, But if I gently accelerate from a standstill it momentarily dies and I have to start her up again.

 

Hey guys,

Ok, XKS Ltd has just informed me that they no longer manufacture the TPS kit and have not taken my money!

Can you guys please give me some advice based on your experiences for the BEST modification unit to use and I will get the ball rolling

Cheers!
Craig

 

It appears I can get this part sent out of the USA and have been told by Diana that it is an OEM part.

Have you guys had any experience with these parts or will they be ok?

https://www.terrysjag.com/product//EAC2670OEM.html

Cheers
Craig

 

Or would this one be better?

https://www.ebay.com/itm/New-Jaguar-...-/192028513344

 

Or this one?

MISCELLANEOUS ITEMS. / AJ6 Engineering