Hi guys.

I had a fuel starvation problem last year with the car stalling etc this was after renewing the fuel pressure regulators. Fast forward to yesterday and the first run out of the season and after swapping the B bank regulator back to the original one. The car ran great all day apart from one incident on the way home when the engine cut out after a second gear run at 3000 odd rpm. I coasted to a halt and the engine started on the third attempt and then ran fine all the way home. Any ideas. I still have the new A back regulator fitted and am tempted to do away with it. Last year I fitted a new fuel pump and fuel filter.

Rob.

 

Hi Robbo

Could be the Crank Position Sensor under the Front Pulley, as its been Freezing Cold and Raining almost every day in April, so may be worth Checking the Gap and giving the Gap a Spray of Contact Cleaner

The Gap should be no more than 0.042

I think you had that same problem a few years ago?

 

Hi OB.

Both the position sensors were renewed last year so don’t think it’s them. When I cranked the engine after the stall on the first two attempts it did try and fire and on the third attempt it started normally and then ran fine. I know when the CPS were playing up the engine would stop and not attempt to fire for around 10 minutes until it had cooled a bit then started and ran fine.

Rob

 

Blocked Air Filter?

Faulty Fuel Pump Relay? and or Main Relay or Corroded Contacts in their Holders (one won't work without the other)

Clutching at Straws Now (Lol)

 

Hi Robbo

Maybe the Pins on the Resister Pack need Cleaning

Cleaning the Contacts on the Resistor Pack which can affect the Injectors

 

Hi OB

Filters all fine and I have cleaned the resistor pack pins so all should be good there. I think I will delete the A bank regulator renew the fuel filter just in case it’s faulty it’s a non genuine part. I could also put my old fuel pump back in as it’s was working ok prior to swapping out. I only did this as preventative maintenance but it seems not to have worked very well. I must admit I am a bit dubious on the quality of pattern parts having had some crappy bushes in the past.

Rob

 

Hi Robbo

Try By-Passing the Thermostatic Wax Stat on the Fuel Rail with a Single Piece of Polythene Tube

Not needed in the UK with our Climate! (Lol) as any sort of Blockage on the way to or from the Wax Stat could affect the Vacuum and make your Car run 'Rich' and as a result cause Starting Problems

I took mine out altogether, as there is nothing behind it (its just blocked off)

I'm actually thinking this could be your 'Best Bet'!

Easy to do, so gotta be worth a Shot

By-Passing the Wax Stat Thermostatic Valve

 

Hi OB.

I have had this out and checked and it doesn’t do any thing so i have worked it for the vacuum to go through the valve without activating it just to keep the car looking original.
To be honest it starts ok either hot or cold it’s the sudden engine cut that’s the problem.

Rob.

 

Hi Robbo

On some Non OEM Fuel Pumps, depending on where it was made, the Positive side is marked Negative and the Negative side marked Positive, so that the Pump can be running in reverse!!!

I've got one of those on my Car at the moment, so all I did was to swap the Positive and Negative around and its been working OK ever since

So maybe that's why your Original Fuel Pump works and your New one doesn't? (This was a Hot Tip from 'Grant' The Wizard of OZ')

Also I only use 'El Cheapo' Fuel Pumps from ebay £30 instead of £130 as they are all Generic and fitted to loads of Cars

Only recommended for Pre-Facelift V12's like we've got, with external Fuel Pumps

Also I've moved my Fuel Pump from underneath the Battery (no re-plumbing required!) So that I can Change it by the Side of the Road if I have to, as I always Carry a Spare one in the Boot/Trunk

Alex

 

Hi Robbo

Pic of my Fuel Pump relocation here, so I can change it by the side of the road if I have to

Fuel Pump relocation to make it easy to get to, if I have to change it by the side of the road

Alex

 

Hi OB
New pump definitely works and is wired correctly. Maybe it has an intermittent fault or doesn’t supply enough fuel at higher RPM. One thing I haven't checked is the fuel pump relay. Perhaps I should renew it as a matter of course.

Rob.

 

Under the trim to the right of the battery on the chassis rail is a huge bunch of earths. Clean back to bare metal and protect with grease after refixing

 

Hi Robbo

Have You Cleaned The Sump Tank Filter but Fuel Pump Relay might be the best place to start

 

Hi Greg and OB.

I will check the earths this weekend and yes the swirl pot and filter are all clean. Can you point me in the right direction to the fuel pump relay please,

Rob

 

Hi Robbo

On our UK V12 Cars

Facing the Boot/Trunk with the Boot Open the Main Relay and The Fuel Pump Relay are behind a Piece of Carpet Trim, just to the right of the Gas Strut behind a Big Plastic Cover, that you can bend back far enough to get you hand in to Change them

The Main Relay is in the Red Holder and the Fuel Pump Relay is in the Black Holder

The Fuel Pump Relay won't work unless the Main Relay (in the Red Holder is also working)

These Two Relays are NOT interchangeable because one of them has a Diode and the other one does not (But this is clearly indicated on the Relay)

There is a Photo of where they are halfway down this Thread

Location of Fuel Pump Relay and Main Relay

 

Cheers OB.

I think the car need a dam good thrashing after being sat over the winter to clear the cobwebs out 🤣🤣

Rob

 

OB, couldn't find your post on relocating the fuel pump, what is the date or number of the post.
Cheers
Alfredo

 

Hi Alfredo

Basically all I really did was to reposition the Fuel Pump Holder, so that it was no longer underneath the Battery Tray and if I can find the Photo you will see that it is very easy to do

But if you are Changing the Pump then you have to be Careful and don't do it inside your Garage, do it outside to be on the Safe Side and then only if you know what you are doing

Including disconnecting the Battery First and having a Fire Extinguisher Standing by in case the worst should happen!

Then Clamp the Fuel Hoses before you disconnect them, as the Fuel Pump is Gravity Fed and if you don't know what you are doing then you could have Petrol Flooding everywhere

So if you are in any doubt, it may be best to leave it as it is

As for Moving the Pump over, as opposed to Changing it completely, from what I can remember I just re-positioned the Fuel Pump without the need of disconnecting anything

The Photo should explain it all if I can manage to find it

 

Thanks OB, hope you find the picture.

 

Hi alpecsa

Here is the Full Post on my Fuel Pump Relocation XJS V12 Pre-Facelift

Fuel Pump Relocation

Also I found the Photo



Hope This Helps
Alex(OB)