Hi OB,
I’m sure there would be other members on this forum, more knowledgeable than myself on the intricate operations of all components that make this complex machine tick, just right.
I can only speculate that as the RH CTS provides input into the Marelli Ignition ECU, which in turn connects to the EFI ECU, it also provides the necessary monitoring of the engine temp adapting the injection timing and firing angle to the operating conditions. As our cars run 2 x ECUs, I assume a dedicated CTS is required, so as not to get false readings that may otherwise occur if each ECU were connected to a common CTS. This would be pretty typical of earlier computer technology cars (eg. Pre the introduction of CANBUS).

 

Hi XJCCAT

Cheers!

I'll have to try and get my head around it although I it is much clearer now than it was before

So Thanks for that

 

Have you really run it cold to 3000rmps and more? Or do you mean, not dead cold, but on the up,,, in the warm up?

Anywho. It's always been described as good practice just to take it out of the loop. All ya need to do is remove it and plug the hose (may have to elongate it) or run another GOOD fuel grade hose from the spout just under the brake pump assembly to the rail. Takes 10min. Removing it decreases the number of things that can go wrong in the fueling and saves a buck or two in idea of needing to replace. Anything to simplify the inside cases over engineered design in a few of the cars systems.

Removing the CATS altogether (if you can get away with it) is a good idea and simply unplugging the 02 sensors in the engine bay takes a second. The car will revert to factory map settings for fueling. Just unplug them. For the CATS, dig and dig and get a set of used euro spec downpipes (eBay or sumpthin) and it's plug and play. You could also gut the cats. Not sure where you are but emissions are not a thing in a car as old.

 

UNBELIEVABLE !!!

Well, I replaced both FPR’s with 2 new ones. Feeling that would resolve the issue of not revving beyond 3000rpm without it beginning to splutter and lose power.
To my utter amazement things are worse! Lacks power down low struggling to even drive a fairly steep street incline in first without totalling dying and stopping! What the ……. ????
I guess I’ll let it cool down and replace the new with the old FPRs and start again. Save spilling fuel over a hot engine and bursting into flames 🔥🔥🔥🔥..

🤔 then again, that might’nt be such a bad thing.

 

My sympathies. But do check you have the correct ones on the correct side, if you do not then this is the likely result.
FWIW, I am strongly of the opinion this fault is electrical, not fuel-related. i am still not sure if you have replaced the HT leads and checked to amp to dizzy loom. If I had to guess, i would still suspect either the CPSs, rotor arm/dizzy cap, or amplifier failure as they get hot.
Nil desperandum!

 

Hi XJCCAT

I'm probably telling you something that you already know but I'd better mention it anyway, as it may be useful to New Forum Members as well as New Owners of V12 Marelli Cars

And so apologies in advance, if it seems as if I'm trying to Teach Your Granny To Suck Eggs (As we say in the UK)

But your Car has all the Symptoms of a Marelli Fire that's about to kick off!

Because for those of you who don't know, the V12 in a Marelli Car, is like 2 X 6 cylinder engines joined together as inside the Distributor is what they call a 'Stepped Rotor' where the Top Half operates one Bank and the Bottom Half operates the other

What could possibly go Wrong!

Due to a lack of Maintenance, like for instance not replacing the hard to get to Spark Plugs underneath the Air Con or even not replacing 'Flaky' Spark Plug Leads, this can cause a Short in the Distributor, as the Arc Created tries to Burn right through the Distro Cap

And in doing so can then Shut Down one of those Banks of Cylinders altogether!

Leaving the Engine Running on just Six Cylinders, which can continue to run so smooth you may not even notice that anything is wrong, except that is for a seemingly inexplicable lack of Power! where the engine may not rev above 3000 RPM ! (Are any Bells Starting to Ring!)

This is a Highly Dangerous Situation and the Car should not be driven, especially if it has Cats!

As though only one Bank is Still Running, Raw un-Burnt Fuel is still being Pumped into the Exhaust/Muffler of the Bank that has Shut Down, which can hold about a Gallon of Petrol!

Which could mean that if that Shut Down Bank decides to Spring into life for only a Second!

Once that Fuel has been ignited, then it could burn your Car to the Ground

So take the Distributor Cap off and see if there are any signs of Arching or the Distro Cap Burning Through

 

.OOPS.

After you swap back to known good units, I suggest "hot wiring" the fuel pump. That is simple to do. Earth the Orange wire of the Pump Relay (Black Socket). That will have the pump running whenever the Ign is ON, so common sense please.

My reasoning:

IF you believe its fuel, removing ECU earthing control of that relay will answer that once and for all.
That is based on what MAY be a signal failure from whatever sensors "talk" to the ECU's to maintain that Earth. If that signal is interrupted at 3000RPM, or some Temp point, then the fuel pump COULD begin to stutter, and cause what you have.

A fuel pressure monitor is going to be needed, and that is NOT easy on these.

Then that infamous shielded wire pokes its ugly head into the arena. I know the Marelli has them, and that's ALL I know of that on your system.
If that thing is breaking down, EXTREMELY unlikely, they generally are ON or OFF, that will give the issues you have.

This is ALL based on my too many years with teh Pre Marelli engines, but the basics be the same.

 

Hi OB,

Thanks for stating the obvious as it never hurts. It’s the simple things that can be missed so no apologies required.
You may see in my earlier discussions all that has been changed to date, including distributor cap, rotor button, spark plugs, etc.. Quite easy to tell if it is running on one bank by simply disconnecting one of the coils or amps and if one suspects a fault on one of the banks, simply sway the amps and coils over and see if the fault changes banks.
Went through all that early on when I acquired this money pit and sorted that, so it’s definitely running nicely on all 12 cylinders, up until it gets up to 3000rpm (when warmed up).

 

OK, have now replaced the new FPRs with the old units and all is back the way it was. Drives nicely up to 3000rpm when it begins to splutter. Go figure! Cheap nasty new FPRs?

Good suggestion re hardwiring the pump Greg. Will give that a go, however if that resolves it, that will open up another rabbit hole to go down. Anyway, will add that to the list of things to try.

Cheers;

 

Loose the regulator on the inlet side to the rail...
How do ya spell lose/loose??? My BRAINS!

 

Hi XJCCAT

Maybe there was a 'Marelli Fire' before you got the Car?

Next time that you Start her up, have a look and see if one of the 'Cats' is Glowing Red, as if so there is a very good chance that one of the Cats has Melted and is Blocking or Partially Blocking the Exhaust

Since we're down to clutching Straws, something else I don't think has been mentioned, is the 'Resister Pack' aka 'The Silver Box' situated down by the Front of the Headlight Nacelle, drivers side on a UK Car that has a Plug and Socket and is quite awkward to get to

This Plug and Socket needs to be Scrupulously Clean (Tooth Brush and Lemon Juice Job) @ 'Grant' as otherwise it can really play havoc with the Firing of the Injectors

Any Crud on the Plug and Socket of the Resistor Pack can play havoc with the Firing of The Injectors

 

JayJagJay

It's 'Lose' (Lol!)

 

XJCCAT

Another Straw to Clutch at: The Ignition Amplifiers on the Top of the Closing Panel

No idea how you Test them or whether they might even solve the Problem, though I do remember reading some where that when you close the Bonnet/Hood

There is so little clearance that their Wires can get crushed and maybe even broken

 

🤔 Well, this doesn’t sound good! What do you think? I took Greg’s advice and hardwired the fuel pump so that it runs continuously, when the ignition is turned on so as to do a bit more fault finding. Without the engine running, one could now clearly hear this!
Not wishing to preempt things, but I think I may have found the source of my grief.
I can feel it in my waters.. 😬

 

Grant's advice! Credit where credit is due...

 

That does sound like a failing pump!

 

Guys,

Just out of curiosity, for an external XJS pump, and bearing in mind how some noise can become exaggerated in videos, is that excessively noisy?

As a TR6 owner (albeit off the road for 30 years!) I'd have been quite comfortable with that level of noise on my Lucas PI pump!

Cheers

Paul

 

As Paul suggests, sound tracks can be deceiving,

BUT

That sounds a very unhappy pump.

Cheap as, Goss, Bosch etc, same as Falcon, Commodore (Aussie guys know these beasts), BMW, Merc, etc etc. NOT unigue to Jaguar in any way.

Maybe???

AND

The A Bank FPR is putting excess load on the pump, well known and discussed over as many years, and that is the reason for deleting that thing.
Your car, your choice, but all my V12's, and there have been many, have had that FPR removed, be me, and the pump does work happier.

 

Paul!!! In my dreams (dreams are only dreams) I have been wanting a TR6,,, with an XJS inline 6 in it... Maybe even one with a supercharger. In your experience,,, is it even possible to fit - in wildest dreams?

I wish I could open the link!

Replace the pump. As Grant says (my Google word suggestion now suggests Francis everytime I type Grant, lol) they are easy to get and cheap-ish... And loooooose the RH FPR... Keep it simple.

 

Something else to check for FREE.

Gotta luv old age.

Get down and look at the steel pipe running under the car from the rear to the front. Just inboard of the sill lip. Its not hidden, its in plain sight.

Tyre fitters, and other Wombats, are too lazy, or stupid, to use the factory jacking points, and when they slide their jacks etc, they usually flatten that pipe. OOPS

That is the fuel SUPPLY pipe TO the engine.

That will give pump noise as it struggles to push fuel to teh front.
A worn pump is also noisy.
Also, the lower volume of fuel has the engine run out of bang juice at some point not far from idle.

A Tasmanian car, years ago, took a while to find, and once found, and a suitable EFI hose with double clamps installed, the beast was alive once more.
3 of mine, Series cars and XJS's have been victims also.

It might be that simple??????

Also check the same pipe on the LH side. Taht is the RETURN line, and overfueling is the usual fault.