Spent the winter working n my XJS. Just recently it has developed a problem that I cant seem to figure out. It will start and run until you turn it off, then it won't restart. Let it set and it might start again and it might not. Then all of the sudden it will start again. It has fresh fuel and filter, you can heard the fuel pump running. Seems to be getting spark. Any ideas would be greatly appreciated, I'm missing something but I'm not familiar with the V12 a all.

TIA

 

Intermittents are frustrating. Tests are valid only when performed while the engine is in 'no start' mode. Fortunately for you, that seems to be a frequent occurance.

"Seems to be..." isn't very encouraging

Step one is to positively confirm spark/no spark ...while the engine is in 'no start' mode....before going down any other avenues

Here's some reading

https://www.jaguarforums.com/forum/x...he-v12-178286/

Also, do you have Lucas or Marelli ignition?

Cheers
DD

 

Hi David

It could be a leaking Diaphragm in the Fuel Pressure Regulator (FPR) on 'B' Bank which may give you enough Fuel Pressure to Start sometimes

And then at other times not

So in a 'Nutshell' a possibility of intermittent Low Fuel Pressure

Or it could be a Blocked or Partially Blocked Fuel Filter always worth changing easy to do and only about £10 (UK)

Or maybe even the Fuel Pump could be on the way out (Aftermarket Generic Pump £30)
again very easy to do

So the First Job would be to Check the Fuel Pressure in the Fuel Rail

A Shop might do that for you for a few dollars or your may be able to borrow a Fuel Pressure Gauge from somewhere

Leaking FPR Diaphragm is sounding quite likely about £50 if you need one and being the one on 'B' Bank its the Cheaper one of the two

The more expensive one on 'A' Bank isn't needed, so that one won't be the problem and can be piped out of the Circuit altogether

So don't go wasting money on a New FPR for 'A' Bank


Fuel Pressure Regulator on 'B' Bank

 

Thanks Guys I will give both options a look. I know I have checked it in non start mode and had spark, but I will check it again. I will also check the diaphragm. I know its a nubie question but which side is the B side.

THA

 

Hi David

'B' Bank is as in the Photo on the same side as the Oil Filler Cap

The only way to check for a leaking diaphragm, is to see what Fuel Pressure you are getting and then see if that Fuel Pressure either holds or starts to slip away

 

Is this a marelli XJS? If so I'd look into the cam sensors my car had a similar issue would start and run fine (cold) then not start again after, also died randomly while driving until that front sensor was replaced. There is one at the rear of the engine to equally annoying to get to.