I have a 1994 XJ6 Jaguar. I don’t know why, but I can’t get fire to the fuel box, on the right passenger side. The wire going to the fuel pump is not hot, and the (brand new) fuel pump isn’t coming on. Could it be the relays?

Thank you.

 

I'm assuming your device has self-corrected "fuse box" to "fuel box" because AFAIK there isn't a "fuel box" on the passenger side.

It could be the relays of course - and don't forget, the oxygen sensor heater relay on the firewall, if faulty, will stop the fuel pump. (you can test the relay socket connections by jumping the connectors with a fused jumper wire)

As your car is a 94 and if it turns out NOT to be faulty relays, my best guess would be that the fuse box on the passenger side has a cracked or cold solder joint.

This is a common fault with late cars.

There are several posts in the archive on how to fix this, but basically you take out the fuse box and at the very back, examine the joints. Quite often the break is obvious but sometimes it is harder to spot. Reflowing all the connections usually fixes the problem, although it's the blowers that usually fail due to fuse box cold joints - but no reason why others like the fuel supply fuel pump circuits could be affected too.

Let us know how you get on, OK?

Cheers and good luck with it

Larry

 

Hi royseals,

Welcome to the Jaguar Forums! It's great to have you with us.

In addition to the relays Larry identified, there are some points in the wiring that can cause problems. One is the electrical connector behind the battery that carries the power from the fuel pump relay to the pump.

Burnt Fuel Pump Connector

Another spot worth checking is the fuel pump RFI Protection Module, which is just a diode and capacitor wired across the fuel pump wiring harness near the connector at the evaporative flange on top of the fuel tank. On our '93 the diode failed, shorting across the wiring harness. You can disconnect the connector at the evaporative flange and the one behind the battery and test that last portion of the wiring harness for continuity on both wires and no shorts across them.

You can download the Electrical Guide at this link:

Jaguar XJ40 Electrical Guide 1993-94

This troubleshooting procedure from Bryan N at the Jag-Lovers forum has always been helpful to me:

XJ40 - '93 / '94 Fuel Pump Circuit Test Procedure

• With ignition OFF
• Remove fuel pump relay (black base, right rear corner
  trunk above BFM)
• Do you get 12 volts at pin 30 (Brown/yellow) of the fuel
  pump relay base from fuse C6 in right fuse box?
• If yes, jump pin 30 (Brown/yellow) and pin 87 (Blue/red)
  in fuel pump relay base - does the pump run continuously?
• If pump does not run, fault is in the wiring / connector
  between fuel pump relay and pump
• If pump runs, suspect fuel pump relay is defective.
• Replace / re-fit fuel pump relay
• Remove oxy sensor heater relay (yellow base on firewall)
• Do you get 12 volts at pin 30 (Brown/pink) of the oxy
  sensor heater relay base from fuse C4 in right fuse box?
• If yes, jump pin 30 (Brown/pink) and pin 87 (Blue/purple)
  in oxy sensor heater relay base - does the pump run
  continuously?
• If pump runs, suspect oxy sensor heater relay is defective
• Replace / refit oxy sensor heater relay
• Remove EMS main relay (black base on firewall)
• Do you get 12 volts at pin 30 (Brown/yellow) of the EMS
  main relay base from fuse C1 in the left fuse box?
• If yes, jump pin 30 (Brown/yellow) and pin 87
  (White/brown) in EMS main relay base
• Turn ignition ON
• Do you hear the fuel pump give its half-second priming
  burst? [You can repeat this many times and you (or an
  assistant listening at the open filler neck) should hear the
  half-second 'whirr' of the pump every time you switch the
  ignition ON]
• If yes, suspect the EMS main relay OR the EMS ECU is
  defective (the latter, very unlikely but possible)
• Turn ignition OFF
• Replace / re-fit EMS main relay
• Remove Ignition 'ON' relay (on a '94 it may be in a
  white base on the firewall or it may be buried under the
  dash behind the radio, which may make the following rather
  difficult!)
• Do you have battery voltage at pin 30(Brown) of the
  Ignition 'ON' relay base?
• If yes, temporarily jump pin 30 (Brown) and pin 87
  (White/pink) in the Ignition 'ON' relay base
• Do you hear the half-second priming burst from the pump
  each time you jump those pins in the Ignition 'ON' relay base?
• If yes, suspect the Ignition 'ON' relay is defective or
  even fuse A5 in the left side fuse box - but if either is
  defective, you will get NO dash lights when you turn on the
  ignition, so you should have already noticed that. --

Please keep us informed, and also please visit the New Members Area - Intro A Must and post an introduction so we can learn something about you and your Jaguar and give you a proper welcome.

Cheers,

Don