XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

Engine splutter and no power beyond 3000 rpm

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  #21  
Old 02-05-2022, 05:32 AM
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Originally Posted by Greg in France
Sorry, to the coils.
Have you renewed the two crank position sensors? These can be heat sensitive.
No haven’t touched the CPS. I have experienced issues with these on a Rover I had once, when they got hot they would breakdown and the engine wouldn’t start at all. I would have thought if they were the issue, it would be similar. The engine would not start as opposed to running ok and start to miss pretty much bang on 3000rpm, would they not?
 

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  #22  
Old 02-05-2022, 05:41 AM
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Originally Posted by orangeblossom
Hi XJCCAT

Now it's onto Plan 'B' The Gap on the CPS Crank Position Sensor on the Front of the Engine, which at the very least may need a Clean with some Carb Cleaner

The Gap should be no more than 0.042

Plan 'C' Coolant Temperature Sensor Pull the Plug off and Test the Sensor with your DVI Meter Set on Ohms, you should get a Resistance of about 2 Ohms, if No Resistance then it needs replacing but also Bridge the Socket on the Coolant Temperature Sensor Plug with a Paper Clip or Piece of Wire
As the Coolant Temperature Sensor Triggers the ECU to open the Injectors to ensure the optimum quantity of Fuel to the Injectors

Bridging that Plug will 'Trick' the ECU into opening, as if the Engine has started to warm up
Thanks OB,
Checked the CTS earlier. Engine warm ; resistance was approx. 500ohm. When hot and started to miss it was around 200ohm. I bridged the harness connector, started the car and still the same issue. Began to splutter at around 3000rpm and lose of power.
No would the positioning of the CPS upon warming up really be likely to exhibit this type of failure?

Cheers;
 
  #23  
Old 02-05-2022, 06:38 AM
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Hi XJCCAT

The Crank position Sensor could easily do that and even worse could literally Switch off the Engine, while you are underway (Ask me how I know or rather don't)

Out of the Two Sensors, it is much more likely to be the Front one just under the Front Spoiler, rather than the one at the rear but give it a Clean and Check the Gap to begin with

Then before you Splash out Mega Bucks on a New One, you can Test the one that you already have, while it is still on the Car!

To do this just unplug it, from inside the Engine Compartment and then Set your DVI Meter to Volts DC and then put the Probes of your Meter on Two of the Three Wires of the Crank Sensor (inside its Socket) the Common one and one of the other two (can't remember which one)

Then get your Assistant to Spin the Engine over on the Key, while you Watch the Meter, where you will hopefully see the reading continually fluctuate up and down as the engine Spins on the Starter, though having said that, its the Gap that could be the problem, that could vary with the generated heat

But again before you go and Splash out 'Mega Bucks' on a New one!

I would go and buy a New Fuel Pump, as you had so much Crud in there that I wouldn't be at all surprised if the Fuel Pump was partially blocked and therefore Not delivering enough Fuel at 3000 RPM

Don't go Spending $200 on a New one, get a Cheap one off ebay for about $30 as these Fuel Pumps are 'Generic' and used on loads of Cars

My el-cheapo Fuel Pump came with a 2 year guarantee and is still going strong 5 years later and I also Carry a Spare as they are so easy to Change by the Side of the Road

Also Consider a New Fuel FPR Fuel Pressure Regulator for 'B' Bank (not that expensive about $50) don't worry about the 'A' Bank one, as that could be taken out of the Circuit altogether if you wanted to and like some of us have already done


The Problem with the FPR is that the Internal Diaphragm can go porous and start leaking Fuel back into the Fuel Tank, so while you may well have enough Fuel Pressure to Start with 30psi if Fuel Starts Leaking back in the Tank, then that pressure may start dropping off and give you almost exactly the kind of Flaky Performance that you are experiencing now

Not the least because that Fuel Pressure Regulator, is in a great position to get lots of Heat which again could cause problems with a Failing Internal Diaphragm

My own Conspiracy Theory is that you need a New Fuel Pump, so may be well worth investing $30 on an el-cheapo one to find out, which in any case is worthwhile to keep as a Spare and obviously far Cheaper than a Tow Truck
 
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  #24  
Old 02-05-2022, 07:32 AM
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Originally Posted by orangeblossom
To do this just unplug it, from inside the Engine Compartment and then Set your DVI Meter to Volts DC and then put the Probes of your Meter on Two of the Three Wires of the Crank Sensor (inside its Socket) the Common one and one of the other two (can't remember which
Thanks OB,

I’ll check and step through all that next. Just by the by the crank sensor is only 2 wire not 3. Interesting explanation on the FPR too, so I’ll look at replacing that and see where that gets me.

Cheers;
 
  #25  
Old 02-05-2022, 09:43 AM
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I'm up and down the east coast today and haven't read word for word alllllll that's been done, so apologies in advance of this has been covered...

Did the inlet FPR get removed/eliminated so ya can rule out a faulty fuel pressure issue at least on one side of the rail? Fuel hose directly from pump to rail on the inlet side?
 
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Old 02-05-2022, 10:03 AM
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Did you ever pull the O2 sensors and see if that made a difference? Clogged cats will cause these kinds of issues. It's free to try, albeit a little noisy for the test.
 
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Old 02-05-2022, 11:47 AM
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Hi XJCCAT

That's a really weird one!

The Plug on my 1990 V12 CPS Crank Position Sensor is a 3 Wire and same on my 1989 V12 while the 2 Wire ones are most normally found on the XJS 4.0L

I'm willing to stand corrected but all V12's are 3 Wire Crank Position Sensors as far as I know, so maybe someone put the Wrong one on or bodged it up, as you did say that the Wiring was in a bit of a mess

Have a look on one of the Jaguar Classic Spares Websites and see what comes up, as if you've only got a 2 Wire CPS instead of a 3 Wire CPS then that could easily be the cause of your problem!

The other potential 'Bear Trap' which is easy to fall into, is the 'Dreaded Coax' White Wire Cable, which is MEGA Important! for sending a Signal for the Injectors to fire at the right time

This goes from the Join in the Wire by the 'B' Bank Air Inlet Manifold in the Engine Compartment to Pin 24 of the ECU and is ONLY Grounded with its Knitted Shielding Covering at the ECU end ONLY!

NOT AT BOTH ENDS!

NOT EARTHED AT THE ENGINE COMPARTMENT JOIN END as your Brain is trying to Convince you that it should be!

Have a look at a bit more detail here with Photos: All about the 'Dreaded White Shielding Wire'
 

Last edited by orangeblossom; 02-05-2022 at 11:53 AM.
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  #28  
Old 02-05-2022, 03:52 PM
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Originally Posted by jal1234
Did you ever pull the O2 sensors and see if that made a difference? Clogged cats will cause these kinds of issues. It's free to try, albeit a little noisy for the test.
No, haven’t done that as yet. Only because it is somewhat awkward to get to and it doesn’t quite feel like that being the issue, particularly as it doesn’t do it when it’s cold. Have a few more things to try before that and if by chance that proves to be the issue, I’ll certainly be eating humble pie. 😬
 
  #29  
Old 02-05-2022, 04:04 PM
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Originally Posted by JayJagJay
Did the inlet FPR get removed/eliminated so ya can rule out a faulty fuel pressure issue at least on one side of the rail? Fuel hose directly from pump to rail on the inlet side?
Hi Jay,
No haven’t done that. So a faulty FPR on the A Bank might cause these symptoms when warmed up and not when cold? Is the A Bank FPR really not required (many say not, including Kirby’s bible). Guess I can bypass that and see how it goes before ordering a new B-Bank FPR, to replace that one in case that is at fault too.
As was explained by OrangeBlossom;
The Problem with the FPR is that the Internal Diaphragm can go porous and start leaking Fuel back into the Fuel Tank, so while you may well have enough Fuel Pressure to Start with 30psi if Fuel Starts Leaking back in the Tank, then that pressure may start dropping off and give you almost exactly the kind of Flaky Performance that you are experiencing now
Not the least because that Fuel Pressure Regulator, is in a great position to get lots of Heat which again could cause problems with a Failing Internal Diaphragm
Only thing is, they are not a $50 item here in Oz, but given what I’ve spent so far, it’s a drop in the bucket. 😏
 

Last edited by XJCCAT; 02-05-2022 at 04:18 PM.
  #30  
Old 02-05-2022, 04:15 PM
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Originally Posted by orangeblossom
That's a really weird one!
The Plug on my 1990 V12 CPS Crank Position Sensor is a 3 Wire and same on my 1989 V12 while the 2 Wire ones are most normally found on the XJS 4.0L
I'm willing to stand corrected but all V12's are 3 Wire Crank Position Sensors as far as I know, so maybe someone put the Wrong one on or bodged it up, as you did say that the Wiring was in a bit of a mess
The other potential 'Bear Trap' which is easy to fall into, is the 'Dreaded Coax' White Wire Cable, which is MEGA Important! for sending a Signal for the Injectors to fire at the right time'
Well OB,
Unless I’m looking at the wrong wire connector (terminating next to the AC compressor on the B-Bank and dropping off down the front of the engine to, I’m guessing the CPS. It is only 2-wire, as is also shown on the wiring diagram.
Re the white coax, yes that was the first thing I found to be at fault and rectified. As a Communications Engineer, earthing the coax only on one end makes perfect sense to me, otherwise it can be subjected to potential earth loops and cause all sorts of erratic behaviour.



 
  #31  
Old 02-05-2022, 05:37 PM
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Hi XJCCAT

My 3 Wire CPS Plug has 2 Pins on the Plug and 2 Wires to those Pins with the 3rd Wire being a Shielding Coax which I was counting as a 3rd Wire

So Yes! you are right but when I cut the Plug off the Old CPS I was looking at 3 Wires, which included the Shielding Wire, my 'Bad' so sorry about the Confusion

As for the Fuel Pressure Regulator, at first glance they look the same although on closer inspection they are different and the one for 'A' Bank which you don't need, is nearly Twice the Price of the one on 'B' Bank which even for a Lucas Brand is only about $30

So if/when you Order one, make sure that you Specifically order the one for the return on 'B' Bank and even send them a Photo of your Old one just to be sure

From Memory the Part Number is EAC4864 but once again double check that its the one that goes on 'B' Bank

The one for 'A' Bank is a different part number altogether, which in any event you won't need

Crank Position Sensor Plug for the Front end of an XJS V12





This is what the Plug looked like when I cut it off the CPS to remove it
 

Last edited by orangeblossom; 02-05-2022 at 06:07 PM.
  #32  
Old 02-05-2022, 07:10 PM
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Originally Posted by orangeblossom
My 3 Wire CPS Plug has 2 Pins on the Plug and 2 Wires to those Pins with the 3rd Wire being a Shielding Coax which I was counting as a 3rd Wire
So Yes! you are right but when I cut the Plug off the Old CPS I was looking at 3 Wires, which included the Shielding Wire, my 'Bad' so sorry about the Confusion
No problem OB. All good to be clear on these things. Appreciating all the guidance being received and once resolved this should hopefully serve as some help for others.

FYI, these position sensors are a simple Hall effect transistor, hence the need for the outer shield to mitigate stray magnetic fields effecting their function.

Have also checked the resistance readings when cold and when hot on both CTS, on each bank and confirmed the wiring back to each ECU is fine per the below;
0 degrees C (32F) 5.9 kohms
10 degrees C (50F) 3.7 kohms
30 degrees C (86F) 1.7 kohms
50 degrees C (122F) 840 ohms
70 degrees C (158F) 435 ohms
90 degrees C (194F) 250 ohms

That’s another thing ticked off as being OK.
 

Last edited by XJCCAT; 02-06-2022 at 12:44 AM.
  #33  
Old 02-06-2022, 04:10 AM
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Hi XJCCAT

I thought there was only one Coolant Temperature Sensor?

What was the one you were checking on the other bank
 
  #34  
Old 02-06-2022, 05:00 AM
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Originally Posted by orangeblossom
I thought there was only one Coolant Temperature Sensor?
What was the one you were checking on the other bank
Nope, there are two.
The one on the B-Bank goes to the ECU located in the boot (trunk for the Americans), connecting to pins 5 & 19
The CTS on the A-Bank goes to the ECU located behind the trim in the passengers foot well at the base of the A pillar. This connects to pins 6 & 19.

 
  #35  
Old 02-06-2022, 07:23 PM
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Regarding the Temp Sensor post.

B Bank = DBC3728 = ECU same as Lucas cars.

Market and Marelli?? dependent, A Bank, just forward of the Temp Transmiitter (Gauge) is DAC4737. This I have never seen in my time, so know nothing of what it really does.
 
  #36  
Old 02-08-2022, 09:24 AM
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(Props to XJCCAT)

I've been looking everywhere for the Elusive Coolant Temperature Sensor on 'A' Bank which was very obviously hiding in plain sight and here it is!



Not so easy to see as it looks in this Photo as its really tucked away down there

This is the more familiar Coolant Temperature Sensor on 'B' Bank that is near the Oil Filler Cap



Just behind the Coolant Temperature Sensor on 'A' Bank is the Coolant Temperature SENDER as opposed to SENSOR that connects to the Temp Gauge in the Cabin




 
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  #37  
Old 02-08-2022, 10:00 PM
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Originally Posted by orangeblossom
(Props to XJCCAT)

I've been looking everywhere for the Elusive Coolant Temperature Sensor on 'A' Bank which was very obviously hiding in plain sight
Coolant Temperature Sensor on 'B' Bank that is near the Oil Filler Cap
Just behind the Coolant Temperature Sensor on 'A' Bank is the Coolant Temperature SENDER as opposed to SENSOR that connects to the Temp Gauge in the Cabin.
Correct OB,
However, neither of these appear to be the cause of my problems. I now strongly suspect it is a fuel pressure issue, after replacing virtually everything else to date, and have order both the B-Bank and A-Bank FPRs to replace. Yes, thought I may as well do both, as contrary to popular opinion here, I don’t believe that the A-Bank FPR serves no purpose and can be totally bypassed.

So let’s see how that goes. Standby for the next instalment. 🤞🤞
 
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  #38  
Old 02-09-2022, 02:12 AM
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Originally Posted by XJCCAT
Correct OB,
However, neither of these appear to be the cause of my problems. I now strongly suspect it is a fuel pressure issue, after replacing virtually everything else to date, and have order both the B-Bank and A-Bank FPRs to replace. Yes, thought I may as well do both, as contrary to popular opinion here, I don’t believe that the A-Bank FPR serves no purpose and can be totally bypassed.

So let’s see how that goes. Standby for the next instalment. 🤞🤞
I quite understand, and why not keep it as stock; but you may not know that Jaguar themselves removed the input FPR on the 6 litre engines.
 
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  #39  
Old 02-09-2022, 03:28 AM
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Originally Posted by Greg in France
I quite understand, and why not keep it as stock; but you may not know that Jaguar themselves removed the input FPR on the 6 litre engines.
Hi Greg,
It is not as much of retaining originality, but more so of maintain correct function and optimal operation.

Yes, I’m aware of the deletion of the A-Bank FPR on the later 6.0L, but that was never the case on the 5.3L and I’ll go out on a limb here and say that deletion of the FPR, was not done in isolation.
ie. what other changes were made to;
- fuel injectors
- temperature sensors
- Program changes/adjustments to each of the ECUs
- EFI fuel pump
- intake manifold design
- fuel rail and fuel delivery system
- etc…
All of which are critical to ensuring correct and seamless operation.

No, for the sake of $110, it is not worth experimenting by deleting a component, that was deemed necessary by the design engineers of the time for no apparent benefit or gain, but more likely a detrimental result that may not really be fully understood.

Don’t get me wrong as I’m not shy of customising and modifying for purpose or benefit, but in this instance I’d be saying it is a definite no, no.

Cheers;
 
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Old 02-09-2022, 03:42 AM
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Hi XJCCAT

Now that I've finally managed to find the Coolant Temperature Sensor on 'A' Bank which I didn't know existed until now

Please could you tell me what it does and 'in what way' a Bad one, can effect the running of the Engine

Does it affect the Fueling or maybe the ignition or even maybe none of the above

As it really is a mystery to me
 
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