Update:
Bought and installed an new Bosch Fuel pump (same as our local Commodores, Falcons), so readily available.
Powered it up and it sounded beautiful and smooth. No grinding or rattling, so was so pleased! Think this has fixed it!!
Took it for a spin and it reved out to 5000rpm, though it still felt like there was a bit of hesitation as it wasn’t as free spinning as my V12 E, but it wasn’t spluttering or missing. Well that’s solved thought I, now just to get it running just right.
Sadly as the car warmed up and I once again floored it going up a hill, I felt a wave of despair 😩 as it started to splutter and miss and not able to rev much past 2500rpm! Seemed to have lost 500rpm in this latest process!

I hard wired the pump, by grounding the orange wire on the fuel pump relay (No difference)
Went around with a spray can of electronic “Freeze” and gave the amplifiers a squirt (in case they were breaking down when warm), but no change.
Fuel lines under the car all look fine and they don’t appear to have been crushed by the wombat mechanics here. (at any rate, if they were the problem it wouldn’t manifest itself only when warmed up)

I’m really pretty much out of ideas now, having replaced virtually everything that I can think of. I hate to say that it has beat me, but it’s getting close.
I might bypass the RH FPR as suggested, but cannot fathom that would exhibit itself as the issue I’m having, keeping in mind I earlier s installed new FPR’s and the car could hardly run, until I reverted back the the old units.

Plumb out of ideas….. 💭

☹️

 

John,

BUGGA.

Goodo on the pump.

It was a straw clutching suggestion list anyway.

Warming up breakdown is as bad as intermittent.
My Marelli knowledge is about what could fit on a postage stamp, but the front and rear crank sensors have appeared very regularly as culprits over the years.

 

Hi XJCCAT

Time for the Longest of Long-shots!

Pilot Error!

Right back at the Start of your Thread you said that you removed and Cleaned the Fuel Tank

Did you mean the little 'Sump Tank' or the Main Fuel Tank or Both Tanks (For as you know the Main Tank) Gravity Feeds the Sump Tank and Then the Fuel Goes to The Filter and then to the Fuel Pump

Where although it may seem beyond belief, we have had a couple of Forum Members who have got the Rubber Fuel Pipe Plumbing wrong, when they went and reconnected all those Rubber Pipes, which is easier to do than some might think, as it is a little bit of a 'Rat's Nest' in there

(1) Double Check the Fuel Filter is on the Right Way Round

(2) Double Check the Plumbing of all the Rubber Fuel Pipes in the Boot and if possible take a Photo of how it is all Plumbed together, as Greg or Grant should be able to tell if you have got the Plumbing of the Pipes connected right

From what you've said about the way She's running, you may have easily wrongly connected one of those Rubber Fuel Pipes in the Boot, which as said is easier to do than some might think
So please take Comfort from the fact that this has happened before and Greg and Grant have took a look and fixed it!

Good Luck and Don't Give Up!

Alex

'

 

Following that thought, another straw to clutch at.

Fuel tank venting.

That is a smoke and mirrors affair. Basically, if the Main tank does not breath/vent as it should, the gravity feed to the pump supply tank under the battery ceases to take place, the supply tank runs very low, the pump starves for fuel, the engine does weird shiiit.
NOTHING to do with when it wams up, just a time thing when the vac in the main tank slows supply to the small tank. Hence the 5000rpm when you 1st went out, then it went AWOL.

Some I have worked on were that way inclined, and out of utter frustration a very long time ago, I took the fuel cap off, went for a blast and NO more issues.
OK, it was Pre HE XJS, not a Marelli beast.

Another note I have in the Grey mater. When Ohm testing HT leads.
Test them cold, write it down, steal the hair dryer, HEAT them up, test again, write that down, compare the numbers, maybe they be getting OLD (like me) and the heat is screwing the resistance..????

 

Yep, done that. Opened fuel cap whilst driving. No change.
Also, thought about the potential of spark leads breaking down, so yesterday replace all of them with a new set. Again, same issue persists.

A bit more reading/research appears o indicate that maybe a fault with the CPS or flywheel sensor. Though, my experience with faulty CPS in my past Rover cars, when engined warmed up the CPS failure resulted in a total engine shutdown. Would not start again until left to cool down. But can a fault here also manifest itself with the symptoms I’m experiencing?

If so, how can I effectively test these sensors to confirm if they are any good?

 

Hi Alex,
I had the main tank removed and repaired by one of our Jag specialist workshops. The sub tank I later removed and cleaned out, as per the photos I had posted earlier in this thread. Reconnection is pretty strait forward, with only 3 lines connecting it, so can’t really get that wrong as they are also different sizes.

 

Hi XJCCAT

Those Crank Position Sensors do cost Megabucks, so its up to you if you decide to replace them

But a very quick and dirty Test with the Sensor out of the Car is to connect your 2 DVI Probes to the 2 Pins in the Plug, where a piece of Poly Tube pushed over the 2 Pins, will give the 2 Probes of your DVI Meter something to Jam into, as otherwise you are going to need 3 pairs of hands to do this! (Lol)

Then Set your Meter to the 'Beep' Setting on Ohms

Next you get a Magnet, a Fridge Magnet will do and then start moving the Magnet ever closer to the end of CPS (without letting the magnet actually touch it) and then when the Magnet is about 5mm away from the end of the CPS you should hear an Audible 'Beep'

Which SUPPOSEDLY indicates that the CPS is OK

There are Two of these Sensors as you know, One underneath the Front Pulley which is easy to get to (in the scheme of things!) and the other one is up near the Bell housing, which you really need to get to using a Car Lift, as otherwise if the Car happens to fall there are no Second Chances!

CPS tends to be a Generic name like ('Hoover Vacuum Cleaners') so make sure that you order the right one and not just ask for a Crank Position Sensor, unless of course that is the one you want because they are not exactly the same to look at

The Front One is the most expensive of the Two although the only real difference is that the Wires hang Straight down

While the Rear one which is much Cheaper and goes in the side of the Bell Housing (somewhere!) has the Plastic End Cranked over at an Angle, so again when its in position, the Wires also hang Straight down, so when you connect the Plugs of these, the Wires take on a Very Slow Curve so they don't get Broken or Stressed

No idea why the Front one is almost double the Price! because apart from the Angled piece of Plastic that the Rear one has, they look the same!

No guarantee these Sensors are going to Solve the Problem, as I think its much more likely that the Engine isn't getting Fuel

Though having said that, this has just Triggered a Thought! and a Cheap one at that!

In the Boot by the Gas Strut is the little Plastic Box containing the Relays (which I assume you have already found) The Red Relay Holder is the Main Relay and this Relay Has a Red Stripe and the Red Stripe indicates that this Main Relay has a Diode

While the Relay in the Black Holder is the Fuel Pump Relay

These Relays are Known as Dual 87's (Thanks to Doug for that)

The Terminals are 30-85-86-87-87

Most Generic Relays are 30-85-86-87-87A

According to Doug (as I myself haven't got a Clue!)

They have to be Dual 87's

As whatever is Connected to 87A is depowered when the Relay is Triggered (no idea what all that means, as Doug is the Expert and I'm not!) so if you need to know anymore its best to send him a PM

One thing that I do know, is that the Main Relay has to be Working or the Fuel Pump Relay doesn't Work (thanks to Grant for that one!)

You could also try blowing out the Fuel Pipes with Compressed Air, just in case they are Full of Crud

Testing the Fuel Pump Relay Testing the Fuel Pump and Fuel Pump Relay inc Photos

 

Has the RH FPR been deleted?

 

When you hook a DMM up to the leads on the TPS and turn the disc do you get smooooooth numbers thru rotation. A dead spot in the TPS?

 

Yes on that one.
Re: RH FPR bypass. Not yet. But why would that be OK when the engine has not warmed up fully?

 

Thanks For the additional suggestions Alex.

I do a basic check on the sensors today, but no need to remove from car, you just need to plug a DMM into the end of the plug and crank the engine over to see if it pulsates, which I expect it will, as it runs just fine when not hot. I think a more accurate check would be when the car is hot and exhibiting the fault, but using an oscilloscope (which I don’t have on hand).
Re the relays, the fuel pump relay does have 2 x “87” terminals, but only one is used so one can use a single 87 terminal relay here. The main relay is as you say, equiped with a diode and it too has 2 x “87” terminals (both used). Also, whether the relay has 2 x “87” or 1 x “87” & 1 x “87a” terminal, they are exactly the same, as a DPST (both connected together. A DPDT relay would however be different, but that is not the case here.

However, as per my earlier post, I bypassed the fuel pump relay, but the problem still persisted.

That said, I did notice that the relay was very hot to touch, and that shouldn’t be the case. Might do a bit more investigation here. Reasons that a relay could be hot is that the fuel pump is drawing more current than it should be (that has been ruled out with a new pump). Terminal contacts could be arcing and breaking down, which may be the case, so I’ll pop in a new really and see. Also, noting that this relay provides power to the oxygen sensors, I wonder if there may be an issue there 🤔

 

Cool. A good smooooooth .32/.36V alllll the way up ta 5V on the TPS? Good!

For the regulators and dampers - I have an ol 928 and the fuel dampers and regulators are super expensive. With that, people have tried all sorts of things to come up with alternatives and ONE of the issues I have read about and heard discussed over and over is differences in behavior one can expect (with the old OE dampers as they go home, and with potential "alternatives") is the potential for irratic behavior once the housings and internals of the FPR and dampers go thru with temperature change. Also, the stiffening or "relaxing" of the diaphragms and bits inside of the bodies of the regulators due to age and temp change.

Also, with age, just like MY old body, the behaviors and actions of things change over time - just like normal. Parts go bad over time.

Then, like you saw, differences in how fuel makes it into and out of the rail, associated pressures and amounts, can make a dramatic difference(s) in running.

It's a "thing" which is why the topic of deleting the RH comes up over and over and has since the car hit the roads way back when.

Then, it's an EASY change/fix and something to not only check off the list in situations like this but also to eliminate as a potential show stopping issue down the road - no pun intended. Why resist it?

For me,,, over time, cleaning grounds has been something that has had a pretty dramatic effect on running - including FI operation/firing... Just like a good thorough cleaning of the resistor pack mentioned, the plug and wiring of the injector harness and it's plugs, the seating of the crank sensors, and close inspection and repair of alllll the wiring that makes it into the V for ignition,,, etc

This thread is now 4 pages long and I am willing to bet my LH pinky toe that the solution is already been mentioned in here somewhere OR is coming up soon,,, AND is a simple one... These cars are, at the end O the day, pretty simple - as a Guru O the XJS once told me.

More than once, after lots O stressing and digging, I stand up straight, slap myself on the forehead and say "DAMN", it was right in front of me the whole doggone one time.

 

Hi XJCCAT

Re: The Spark Plugs

The XJS does not like those Fancy iridium Plugs with the 3 Prongs and we have heard of XJS's that won't run properly with them in, as the XJS prefers 'Bog Standard' NGK BR7EF or Very Similar for OZ that Grant Can Advise on because of Climatic Conditions: NGK BR7EF

Re: Coils near the Capstan (Check for a Bad Earth)

The Lower one (The Red One) goes to 'A' Bank

The Upper one (The Yellow One) goes to 'B' Bank

The Stubs on top of the Dizzy for the HT Leads to the Coils: The Long Stub does 'A' Bank and The Short Stub does 'B' Bank

I also Agree with 'Jay' The 'A' Bank Fuel Pressure Regulator (FPR) needs to be removed and taken out of the Loop, if for No other reason than a process of elimination just to see if it makes any difference as something inside it may be restricting the Flow

You can always put it back afterwards (or even better replace it with a New one) if you really want to and want to keep things Original, as I would be totally Gutted, if I had just spent $300 on a pair of Crank Sensors, only to find the the Fuel Pressure Regulator (FPR) on 'A' Bank was the problem all along

Also Check all the Vacuum Pipes on the Fuel Pressure Regulators

The Crank Sensor and Flywheel Sensor: The Rear Sensor Monitors The Engine RPM for the ECU and the Front Sensor Triggers the Injectors and the Spark

So the Rear one needs to be Working to Initiate the Front one (in very simplistic Terms) Just wondering if that 'Could' be a Breakthrough Moment?

We have just got to keep on churning this stuff, if nothing more than in the hope that someone has a 'Light Bulb Moment' as I have a feeling that the problem could well be a Very Simple Fix

Let's hope so anyway!

Good Luck

Alex

 

Yep, have checked and tried soooo many things to date, but it still not resolved. Just to recap;

The Problem as it currently stands:

When first going for a drive, out the drive way and up our steep hill, car drives fine and can easily spin out to 5000rpm in first. Though with the foot flat to the floor it feels to be held back a bit, with it accelerating better when you back off the throttle to say 3/4. (Bit weird)
Once around the block and warmed up (and we have a reasonable size block: about a 5km drive), trying to accelerate in first results in it starting to splutter and miss at around 3000rpm)

So What's been done to date?

1. New Distributor Cap & Rotor Button
2. New Coils
3. New NGK BR7EF Spark plugs gapped @ 0.025 (replaced twice, in case there was one faulty)
4. New Fuel filter
5. New Spark Leads
6. New return Fuel Pressure Regulator (FPR) A & B-Bank (made things worse and replaced with old FPRs)
7. Removed and bypassed A-Bank FPR altogether
8. New Fuel hoses throughout engine bay
9. Cleaned and checked PCV
10. Noisy Fuel Pump, replaced with new Bosch pump
11. New Fuel Pump Relay
12. Cleaned Power Resistor Pack Connectors
13. Sprayed Amplifiers with can of freeze when hot, but missing at 3000rpm issue persisted
14. Rewired Thermo fan to operate correctly off thermostat temp switch
15. Repaired white coax connection in engine bay harness going to ECU
16. Repaired/Resoldered Common point mess of wires terminating in bunch in engine wiring harness on B-Bank side (dry joints)
17. Replaced Bosch connectors to both Coolant Temp Senders (CTS)
18. Checked both CTS for correct resistance when cold (28 deg) and @ 80 deg and continuity of harness connection to their respective ECU's
19. Checked and confirmed Air Temp Sensor
20. Cleaned out fuel tank and sub tank (including internal strainer)
21. Blew out fuel lines with compressed air
22. Checked operation of vacuum line to both ECU's (located in boot and passanger footwell)
23. Checked and confirmed fuel pump voltage same as battery terminal voltage
24. Hard wired fuel pump relay, connecting orange wire to earth so that it runs when ignition is turned on to fault find possible issues with ECU (no change)
25. Serviced and corrected issues with all 12 EFI Injectors
26. Installed new EFI engine wiring harness
27. Checked and set TPS ensuring voltage b/w red & yellow wires is 0.34V and maintains continuity through to open throttle (approx. 4.7V)
28. Set both throttle linkages to be the same (synchronised)
29. Corrected back to front install of air filters
30. Checked and cleaned wiring earth points near headlights
31. Checked and cleaned earth point next to battery
32. Checked all fuel lines under car are in good condition

There’s probably a few more things I've done but that wonderfully elusive gremlin, that those Leyland boys installed in every Jaguar that rolled off the production line at the time, continues to evade me! Now there has been a lot suggested by this group, for which I am really greatfull to have had company on this rather frustrating journey and much of what I have checked, fixed and or replaced would no doubt have had to of been addressed at some point so its good to have gone through all this to date. But still, no cigar!

I'm pretty sure I've attended to all suggestions to date, save for the potential of checking a blocked exhaust (just not convinced on that one), or maybe issues with the CPS or FPS. I'll keep this in the back pocket at the moment, but what else has now come to my mind (and I don't believe it has been suggested) is possibly faulty O2 sensors. Reason I'm thinking that is as they warm up, and become erratic, they may be sending incorrect info to the ECU, which in turn is giving all the wrong instructions to the injectors and timing. Possibly why the fuel pump relay seems to be unusually hot and the car doesn't accelerate as well at full throttle as what it does at 3/4 and begins to miss and lack power.

Anyway, I might head down that rabbit hole next and see where it leads. There's been a few dead ends to date though and this may well be just another one of those. Rapidly running out of options now.

 

Not much else to check.
You could put ice around the ECU.

 

Hi XJCCAT

Have you ever had this Car running properly, or did these problems only occur after you had the Fuel Tank Cleaned

As believe it or not something like that could be the cause of the problem especially if some sort of Coating was applied to the inside, as if that Coating starts to dissolve then there are a lot of things that could start getting blocked up

The reason that I say this, is how could a Car ever run any worse, with a New Fuel Pressure Regulator than it did with the Old one, which seems to be sort of bordering on the impossible

'Not a lot of people know this' but you can still buy New Fuel Tanks and in the event it may come to that, Greg knows a source of supply

Though since you are this far into the game, I really think your next move before you go any further is to check the Fuel Pressure with a Fuel Pressure Gauge

 

Damn. That's a lot. Quick question. Maybe the question is answered at some point in the previous posts but sometimes it is just easiest to ask (and I'm lazy). Has the car ever run correctly since you've had it? Or better, when did things change and what was happening or happened when or just before?

 

XJCCAT,

The issue of when the problem first arose, and also the change in symptoms when things have been changed / adjusted is perhaps the best way to look at this.

I'm sure you don't need any more distractions but I know there are many of us who are intrigued by the issue and what the outcome may be! I know this probably doesn't mean anything to you but after reading and re-reading the thread, my money is still on an obstructed fuel pressure delivery at revs or else a blocked exhaust!

Continued good luck!

Paul

 

I think the possibility of faulty sensors was mentioned... Just unplug them under the hood and the car will go into a "default" fueling map based (I think) on revs, load and engine temp - the signal from the coolant temp sensor... Also, with a DMM you could get the car hot and take a reading at the sensor plugs under the hood. Should be fluctuating .1 to .9 amps,,, I think. BUT, having had bad O2 sensors, I don't think the car was as effected as dramatically as what you've described.

Weather hot or cold, running at idle and in park, do you get a smooooooth exhaust note or are you hearing any popping and misbeats at the rear of the car where exhaust exits?

 

Many years ago I had a very fast Range Rover, and afetr a service it would not pull over about 80 mph. It seemed Ok for a bit but then would not pull at high revs and high loads. It turned out to be a duff new Bosch fuel filter than was self-clogging because the element inside was malformed. I would fit a new filter for sure.
Have you checked the connector into the Marelli ECU in the footwell?
Still I say change the HT leads for new ones.
Still I do not completely believe that your verifying of the amplifiers proved they are not the trouble. My money on the amplifiers and their associate wiring as the symptoms are what you would expect from an electronic component breaking down as it heats up.