So my 92 XJS V12 has had a complete ignition refresh and has been suffering from the extended cranking before starting. Part of the refresh happened to include a cam position sensor as the shop owner could not get the car started and this apparently solved it. (This was several weeks ago and maybe 400 miles of use). Now, since then I have been driving the car daily, and it generally cranks several seconds before starting. During the cranking you can hear one, two, ore more cylinders firing before it ignites all 12. However, on a few occasions the cranking has a different sound, with zero cylinder fires, and makes me feel as though it is just not going to start. So far, on three or four occasions after several attempts, always cycling the fuel pump multiple times before cranking, it gives me this impression it will not start. And it simply does not fire at all. Then, mysteriously we either wait, or keep trying, and it's back to the usual starting sounds and experience.

So, today my friend had the car parked at his work all day and I had gone over this with him previously, and of course it happened with him. The car would not fire. As I sit here typing, he calls back and reports it eventually fired up.

What could possibly cause an intermittent situation like this? I am convinced it is more than cycling the fuel. On at least two of these situations the car had sat all day without running, so it was not in a hot state.

Normally in the morning when I start, the car purrs so nicely I begin to think how nice it must have been when new. I can not trust this car.

 

Hi gccch

It sounds as though you might need a new Fuel Pressure Regulator on 'B' Bank as if the diaphragm on this is leaking (internally) then you may not get enough Fuel Pressure to Start her 'on the button' every time

You won't need one for 'A' Bank and in fact you may not have one on your 92 as that was done away with on the later Cars

 

Thanks OB. My shop checked the FPR and it is working. Not sure I made my point clear but this seems very different than the extended cranking I "usually" get when starting warm.

 

Have you tried priming the system before starting? Turn the key to the run position for a few seconds, turn the car off and repeat a few times then try starting it. There is an anti backflow valve in the system and when it goes bad, the systems looses it's pressure.

 

Assuming the FPR/injection really is OK, and it might well not be; then something in the ignition system is giving up. Have you renewed the amplifiers and checked their looms? Also, have you renewed the rear CPS and checked its clearance? Also have you cleaned the resistor block connector and socket?
https://www.jaguarforums.com/forum/x...sistor-134745/
When it does not start, whip out a plug and see if it is wet. If not fuelling problem.

 

Greg, By amplifiers, I think I would call these ignition coils? They were replaced by the Jaguar Doctor when he replaced the front CPS. I did not know there was one in the rear. So I will need to find that. The wiring for injectors and coils has been checked and is in good shape. Also I do not know anything about the resistor block.

As this situation I am describing seems intermittent, it could be I am simply wrong about that but when you begin to know your car there are things you can sense better than explain. I appreciate you suggesting these places to look. This is exactly the guidance I am looking for.

I also suspect it may be a fueling problem but more concerned I am off track and have a complete electrical failure looming.

The fuel cap is sealed, not vented. I read another post where a vent was created. Mine out-gasses when I open it, so it is generally under pressure after running. Not sure if this is how it should be or if it could be a factor. Again, this situation has occurred at least twice after the car sat in the sun not running for 6-8 hours. So it was not a warm start. Usually a cold start is when it runs best.

I have been considering a fuel injector service. Perhaps this would be a good next project.

Thanks,
also Greg

 

Amplifiers are the two small rectangular things on the radiator closing panel with looms to the dizzy (see 2 below), 1 below is the single type of ignition coil, which is on the throttle capstan pedestal. your car should have been fitted at the factory with the single coil, so maybe you and your garage are confusing the amplifiers with coils. If the amplifiers or their looms are on the way out: no spark. Before you start doing anything more though, find out if your problem is fuelling or spark, by checking for a wet plug.

You should find either plug A3 or B3 can be accessed quite easily. But the rear CPS is a MUST to check/renew, and the gap is crucial, I think Baxtor or Warrjon can advise in detail. The rear CPS reads off the flywheel (actually called a flexplate in an automatic car). This posted by Warrjon on an earlier thread might be useful: https://www.jaguarforums.com/forum/a...relli-info.pdf

You can eliminate fuel tank venting causing fuel starvation by loosening the filler cap a touch and seeing if that fixes the problem.

 

Hi gccch

Not sure what you were meaning about an ignition refresh?

What exactly did they do to your Car?

If they only put in a New Crank Position Sensor, then I feel that they may have been 'barking up the wrong tree' or else your Car would now be running without any problems and Starting 'On the Button' first time every time!

I'm still suspecting a leaking (internally leaking) Fuel Pump Regulator on 'B' Bank

As while it may appear to be OK and shoot fuel out of the Pipe, if that's the way it was Tested by your Shop then that Test is pretty meaningless, as that FPR (Fuel Pressure Regulator) needs to be shown to Hold Vacuum

The Question you need to ask of your Shop, is did they Test that FPR with a Vacuum Gauge and if they didn't do that you are in 'Never Never Land'

You need to insist they Test it with a Vacuum Gauge, while you are there watching as that FPR must hold Vacuum for a sustained amount of time (as if the Vacuum drops off quickly) then that could easily be your problem right there

Many Shops don't have a Clue about working on these V12's they may have never seen one or worked on one before

There is a great big list of things that have to be gone through, one at a time and slowly or you or they could easily find yourself skipping over the very thing that's stopping her from Starting (First Time Every Time!)

I had to learn this the hard way myself and if it wasn't for 'Greg' and 'Grant' my Car 'Cherry Blossom' would not be on the road as I knew nothing about engines or working on Cars

(1) Don't start throwing money at your Car until you have identified the problem, which need not be difficult BUT only providing that you do not leave any Stone Un-turned

(2) When you turn the Ignition ON can you hear the Fuel Pump Running?

(3) When the Car is running, if you get out and open the Boot/Trunk can you hear the Fuel Pump Running consistently without any 'Hiccups'

(4) When did you last change the Fuel Filter? Always Worth Changing, only a few dollars and another 'Prime Suspect' for a Bad Starting Scenario

(5) Have the FPR Tested with a Vacuum Gauge (it must hold Vacuum for a sustained amount of time) not just enough to 'Appear to be Working' in the eyes of a Shop who may not know about these Cars

(6) Check ALL the Vacuum Pipes (for Vacuum) especially the one that goes on the back of the FPR, if you pull the Vacuum Pipe off the FPR you should be able to get at least an idea, if there is any Vacuum there or not

(7) Another 'Prime Suspect' is the 'Plug and Socket' on the Resistor Pack, as mentioned by 'Greg' which is the 'Silver Box' down by the 'Head Lamp' Nacelle (overlooked by many shops) who may not even know what that Box does

And its also a bit of a PIA to get to BUT it is repeat a 'Prime Suspect' in the case of bad Starting, so that Silver Box needs to come out and have its Plug and Socket cleaned until they look shiny and new (see photo)




The 'Resistor Pack' on an XJS V12 the Plug and Socket need to be thoroughly Clean!

Less likely but also possible are the Ignition Amplifiers, which are on the Top of the Front Closing Panel but as they are fairly expensive and no way I know of testing them, except by swapping them out, I would leave those to last (see Photo)



The Ignition Amplifiers on a Marelli XJS V12

You can see the Resistor Pack and what it looks like about half way down Page:87 of my 'Cherry Blossom' Restoration Thread and here is a link to that page Cleaning the Plug and Socket on the Resistor Pack of an XJS V12

There are also Two Coils on a Marelli Ignition System just underneath the Throttle Pedestal one for each Bank of Cylinders and there is a 'Possibility' that one of those Coils may be faulty

But before you do anything else, do the Test that 'Greg' has told you about, then at least you will know if its Fuel or Spark

Also do what 'Greg' said about the 'Crank Position Sensor' as there are 2 of these on a V12 one underneath the Flywheel and the other one on the Back of the Engine but I would let a Shop change that

As its a PIA to get to and I'd much rather have a Shop do that (for Safety on their Ramp)

 

 

Can you elaborate a little on this please Greg. As you know I am trying to recommission my v12 at the moment and have noticed today a strong smell of fuel coming from the filler cap. The cap when pressed down will shut completely and I presume not leak fuel vapour. How should it be? Does it need adjusting. Thanks[/QUOTE]
The OP was worried that his fuel breather/vapour purge system was blocked and thus not allowing air into the tank to replace the fuel used, resulting in fuel starvation owing to low air pressure in the tank. As long as your system is not creating a partial vacuum in the tank, nothing to worry about. If it were, a test with a loose cap that prevented such a partial vacuum would prove the breather system was not working properly.

 

To summarize what was done by either me or the Jaguar Doctor,
1) New spark plugs, wires, rotor, cleaned original Marelli cap
2) Jag Doc replaced the coils as they were failing when I brought it to him.
3) Jag Doc replaced from Cam Position Sensor. He says the rear is actually an engine speed sensor. So not sure who's got that right. He does nothing but vintage Jags, and is well respected by the club members here. He had no spark and no injector pulse, then tested the CPS to confirm it had failed.
4) JD also did AC work and exhaust clean out and repair but not related to this current concern.
5) JD repaired a fuel leak where the last guy did not have the correct o-ring seal available. This was the inlet to the fuel rail at the FPR. 92 has only one FPR. Maybe that's the outlet side? Passenger side of engine.

When I just cleaned out between my radiator and heat exchanger for AC, I removed the plugs for the amplifiers and they look good. There is dielectric grease in there and it all looks like it has never been dis-assembled. All cable ties and hardware was complete and consistent. Not sure how to check for function but JD told me he does not recall having issue with one of those. Hmm.

My fuel filter and pump are new as well after a complete rebuild of the in tank assembly. Someone HAD been in there and it was a mess. It's all correct now.

Fuel tank builds pressure, as the cap will outgas upon removal.

Next I will check the resistor pack. I looked at it and it looks not too difficult to get out. Also will check a plug next time this happens.

I don't have a way to test the vacuum on the FPR....

 

Hi gccch

You can pick up a Vacuum Testing Pump fairly inexpensively abt $20 on ebay/amazon/parts shop/Rock Auto etc

Just wondering if your 'No Start' problem may be related to your engine overheating problem?

 

Thanks for the recommendation... and No, I don't see how that would be related to overheating. As I mentioned this happened twice now after the car sat for 6-8 hours.

 

Hi gccch

Is your Fuel Rail fitted with a Thermal Fuel Enrichment Switch?

As I had a Fuel Problem on my Car 'Cherry Blossom' that was caused by this very thing, which seemed to take for ever to track down

Basically what happens is that this innocuous looking switch that Screws into the Fuel Rail, cuts off the Vacuum to the FPR when it gets Hot and then this loss of Vacuum increases the Fuelling in the Fuel Rail to help with a Cold Start

So far so good But this Thermal Fuel Enrichment Switch is filled with WAX (It's meant to be filled with WAX) but what happened was that this WAX melted out so the Switch didn't work

The Result was a Very Sweet Smell under the Bonnet/Hood followed by a very loud Bang! and intermittent Back Firing

As we don't have a 'Hot Start Problem' (very often) in the UK, I just took that Switch out and then just joined the two Vacuum Pipes together (which instantly solved the problem)

There is nothing at the back of this switch, its just Blanked off where it screws into the Fuel Rail

So if your Car has this WAX Filled Fuel Enrichment Switch, your Overheating Problem 'Could' have caused that WAX to melt out which could result in the Fuel 'Leaning Out' resulting in Poor Starting

So I wouldn't rule that out if your Cars Fuel Rail has that Switch

You can read all about what happened as well as see all the Photos about half way down Page: 87 on my 'Cherry Blossom' restoration thread 'Sweet Smell followed by a Bang!'

Here is a Link to that Page: Fuel Enrichment Switch caused Starting Problems 'Sweet Smell Followed By Loud Bang!'

 

I think this Fuel Enrichment Switch was removed during the refresh for 92. My car does not have one.

 

Hi gccch

With your Car in such a hot Climate, then maybe the Fuel Enrichment Switch could be what it needs but in any event when they took that out, did they join those Vacuum Tubes together, or the FPR is likely to malfunction

 

This car never had that device as far as I can tell. Maybe part of the improvements that came in 1992.

 

Never mind what the rear sensor is called, the car will not run if it is not working properly.
Fuel tank outgas is actually far more likely to be fuel tank partial vacuum, it is very hard to tell the difference, test with a loose cap.
If your car is RHD, then the single FPR will be on the passenger side (ie B bank, the LHS as you sit in the car). If your car is LHD, and you REALLY only have an FPR on the A bank side, and you REALLY have none on B bank, then there is one of your problems right there! This photo shows the B bank FPR, the one you should have!

 

 

Sorry, I did not realise the 92s were different, I would be grateful for someone to explain the FPR setup in these later V12s.
If it starts Ok cold, and not hot (I had not realised this either) then I would definitely suspect fuelling first. Where ever the FPR is, I would renew it. Also, when hot, cycle the ignition on for a few seconds, then off and on again several times to push cold fuel into the injector rail. Then floor the throttle and try to start it. All the wile keeping the fuel filler cap loose to ensure no tank vacuum.
This link is about the hot start system on later models, in case it is useful:
https://www.jaguarclassicparts.com/u...stem-5-3-litre