I have an early X308 XJR (RHD) that has been sitting for quite a while (a couple of years) that will not start.

The dash lights up OK and the engine spins on the key.

I have checked the Schrader (?) valve on the injector supply pipe and there is no fuel following 20 seconds or so of cranking.

I have checked the Relays in the boot fusebox and noticed the following:

Ign switch turned to IGN (II?), Relay 4 in the boot operates for about 2 or 3 seconds and then releases, I can measure 12v on Fuse 15 with the relay energised. Relay 1 (the 2nd Fuel pump relay which is only used in SC models) does not operate at all. (JTIS 310-01 has the wiring diagram, J.303.1153)

I have swapped Relay 4 and Relay 1 (General relays) and the symptoms stay the same.

The result is no fuel to the injectors...

I have noticed that the 'pressure' in the fuel tank appears to increase when I follow this process. I noticed this by removing the fuel filler cap where a significant amount of air is released.

The fuses (F7 & F15) are good and I am picking up an earth at the fuses with the relays de-energised which I assume is via the fuel pump windings.

Any ideas why the fuel tank should build pressure like that? It is very similar to when you remove the fuel cap on a car that is almost empty but pressure rather than vacuum.

Thanks in advance

Nigel

 

so you see no pressure at the rail and swapping the relays doesn't change a thing? and you checked the fuses? well I would suspect a bad fuel pump next, you should try and take the covers out of the trunk and see if you see power at the white connector that eventually leads to the top of the tank (i.e. the pump). Why would the pressure in the tank increase? The vent system for the fuel tank in your car. There is a vent valve that becomes plugged and makes the pressure in the fuel tank increase. I think you have two problems.

Best of luck!!!

 

Hi Daxter1987, thanks for getting back to me.

I'll remove the boot lining covering the tank and check the wiring at the last point before it goes into the tank.

I also need to understand the pressure release mechanism... I am a little baffled as to what might be causing the pressure in the first place? I had wondered if one or both of the pumps were operating in some fashion to create the increased pressure?

It appears to me that the ECM is operating the first relay, a pump is then possibly building pressure in the tank (not in the rail), the ECM is notified by a pressure transducer somewhere that a particular pressure is achieved and the ECM shuts off the pump??? (or maybe I am reading to much into all this?)

I have looked through the JTIS but haven't seen a detailed description of the process of operating the pump(s) and how the ECM manages the pressure... It would appear to be more than just simply operating the pump(s) all the time the IGN is on...

Thanks again

Nigel

 

I honestly think you have two problems not just one. Keep your mind open ot you'll go crazy (tell you from experience )

 

If your car is a XJR then you have 2 fuel pumps in the tank. From what I understand you can bypass one pump and make the second pump kick in to get you home or to the shop. See Fig 04.7 from the link below. I would recommend that you check the wiring to the pump internal & external to the pump I understand a few cars had problems with them as well.

Link http://www.jagrepair.com/images/Auto.../jagxj1998.pdf

As for the pressure in the tank that is another problem as suggested by others.