I have a 91 xj6 4.0 liter. I' m not getting any power to my fuel pump. Fuel pump fuse is not blown and the fuel pump relay is activating when you turn on the key. Relay has been checked to be sure contacts are good. Any ideas on what else it could be? Ecu? Another fuse or relay that I'm not aware for?
Thanks,
Keith

 

Inertia switch?

 

Hi Keith,

The fuel pump relay socket should always have battery power on terminal 30 (the terminal to which the Brown/Black wire is attached). You should be able to measure at least 12V from that terminal to a good ground, such as the ground stud in the rear right corner of the trunk below the tail lamp.

The battery power comes from fuse C8 (25A) in the left hand fuse box (at the base of the driver's door A-pillar). If the fuse is good but you do not have 12V at the fuel pump relay socket, suspect a problem in the wiring between the fuse box and relay or a problem upstream from the fuse box, such as the main relay or inertia switch, or in the ground path of the ECM, such as the ignition switch.

If you have 12V at the relay socket, you can test the fuel pump and the wiring between the relay and the pump by carefully jumping across the socket terminals 30 and 87 (the Brown/Black wire and the Blue/Red wire). You can make a jumper wire by bending a paper clip into a U shape and wrapping the middle section of the U with electrician's tape or duct tape as insulation. Hold one end of the paper clip in the terminal for the Brown/Black wire, then carefully touch the other end of the paper clip to the terminal for the Blue/Red wire. You should hear the fuel pump run.

If the pump does not run, there is a problem either with the pump or the wiring between the relay and the pump. A very common problem is the electrical connection at the evaporative flange on the top of the fuel tank. It is not easy to reach, but if you disconnect the bolts that secure the two metal straps that hold the fuel tank in place, you may be able to lift the insulating pad on the top of the tank just enough to see the electrical connection on top of the tank. On our '93, I can just reach the connector with my fingers to disconnect it. With the harness disconnected from the top of the fuel tank, use a flashlight to inspect for signs of arcing on the connector on top of the tank.

If all looks well, with the fuel pump relay installed and the key in Position II (Run), test for 12V across the terminals of the wiring harness connector that you disconnected from the top of the fuel tank. There should be 12V between the Blue/Red wire and the Black wire.

If you don't have 12V at that connector, turn the key to the off position and remove the fuel pump relay again. Test for continuity on the Blue/Red wire between the relay socket and the fuel tank connector. Then check for continuity between the black wire at the fuel tank connector and any good ground (the negative battery terminal or any of the ground studs in the trunk). Finally, check for a short between the Blue/Red and Black wires by putting your ohmmeter probes across the terminals of the fuel tank connector.

If you have 12V at the relay socket and the wiring between the relay and the fuel tank connector is OK, then you either have a problem with the electrical connection on the top of the tank or the fuel pump is bad.

You can download the 1991 XJ40 Electrical Guide at the link below, courtesy of jagrepair.com, hosted by our member Gus. You'll find the fuel pump wiring schematic on page 71 of the pdf file:

http://www.jagrepair.com/images/Elec...Electrical.pdf

Hopefully some of our members with '90-'92 cars will chime in with additional information or corrections. I'm currently dealing with a fuel pump problem on our '93, but the wiring is a little different compared to the '91 cars.

Please keep us informed!

Cheers,

Don

 

Thanks Don & jag fixer, I'll do those checks and let you guys know. Thanks so much for your help!!! I miss driving my jag already. I love that car. I which they made an after market rear sway bar. I sized up my front sway and it really helped to increase my speed thru the corners.

 

Keith,

Search the forum for "monostrut" to read about the revised differential support for the X308, which replaced the two separate "dogbones" or "bushed differential struts" with one large brace.

Here's the XJ40 diff support, which uses two separate dogbones, Part 14. The dogbones are an important part of the independent rear suspension, since they allow some movement of the rear subframe/diff carrier but limit that movement:




And here's the X308 setup, with one large "monostrut" or "bushed differential strut," Part 13, that stiffens up the rear end by minimizing the movement of the diff carrier/independent rear suspension:





Also, the X308 rear subframe bushes, Part 13 in this diagram, are supposedly an improved, stiffer design and are a direct upgrade for the XJ40:




All of the above diagrams are from jaguarclassicparts.com, the parts service of the Jaguar Daimler Heritage Trust, which is a great place to look up exploded diagrams and part numbers.

Cheers,

Don

 

Don, I surf the salvage yards a bunch. I'm gonna be on the look out for that mono strut. Thanks again for that upgrade tip. I'm truly appreciate it.

Keith

 

If you don't find one in a salvage yard, check eBay - the monostruts are frequently listed in the $40-$90 range. Here's a current example:

98 03 Jaguar XJ8 4 0L V8 Engine Rear Crossmember Differential Carrier Bracket | eBay


To find all the listings, you have to try different keyword combinations, like "Jaguar differential bracket," "Jaguar rear brace," "X308 diff mount," etc.

Cheers,

Don

 

Don, I figured out the problem with my fuel pump. The wiring harness that goes to the fuel pump in the trunk had a bad ground connection. Thank You for telling me to do the continuity checks from front to back. The connection was corroded due to moisture. Without your advice, I would still be dead in the water.
Thanks so much!!!
Keith