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Fuel Supply and Fuel Pump FAQ

Fuel Supply and Fuel Pump FAQ

by Mark Chiampi

Electric Fuel Pump 

These instructions assume you have a newer, fuel-injected model XJ and are converting it to a carbureted engine using an electric fuel pump: 

If you plan on using an electric fuel pump instead of a block mounted mechanical one-- you will need to use portions of the Fuel Injection wiring harness and relays mounted on the firewall. You will need to retain the (2) "Fuel Pump" relays next to the large "Starter" relay. One of these relays (possibly red) can be identified by finding a large wire going from it to the (larger) "Starter" relay. And, the other relay has a white/purple lead that goes from it to the first relay. The black wire that goes to the unused 3rd relay needs to be grounded and that relay removed. Save the large white and white/green wires going through the firewall-- the rest can be cut. The fuel pump in the trunk would also need to be replaced with an non-fuel-injected version (assuming you are using a carbureted engine). See the Fuel Supply section for further details. 

The advantage of using the existing Jaguar circuitry is safety; this maintains the fuel shut off circuit that shuts off fuel flow in case of a severe accident. The "Inertia Switch" that does this is located inside the passenger compartment on the passenger side between the front door and the dash. 

If you wished to install an anti-theft switch to shut off the fuel pump, you would splice it into the white/purple wire at the relays. 

You can remove the remaining fuel injection wiring and ballast resistor from the engine compartment, as well as the ECU unit from the trunk. While in the trunk, you may also remove the small brass cylinder with the two red wires coming from it. This is a blasting cap for Jaguar’s SDD (Self-Destruction-Device). Really it’s an altitude sensor. 

Fuel Supply 

WARNING! Fuel vapors are very flammable and pose a very real hazard. Avoid fuel spillage and wipe up any that occurs. Ventilate any contaminated area before continuing to work. Vapors are heavier than air, and will collect in the spare tire well. Use vise-grip pliers to pinch off rubber fuel lines while you work on them to avoid spillage. 

If you have a fuel-injected model XJ, remove the fuel pump, fuel filter, and return valve from the trunk. Replace them with pieces of 5/16" fuel line and a ½" to 5/16" adapter (see below). Attach the fuel tank selection switch to the metal line going to the right side of the engine compartment. Install the fuel pump in-line using the existing wiring and the necessary 5/16" fittings and fuel hose. It would also be a good idea to install a good see-through fuel filter and pressure regulator (if the pump is not equipped). Purolator Performance makes a nice filter and regulator. 

A fuel line adapter can be made by using a ½" hose to ½" NPT fitting, a ½" NPT to 3/8" NPT bell reducer, and a 5/16" hose to 3/8" NPT fitting. Seal the threads using Teflon tape.

Block off the disconnected fuel-return line in the trunk (coming back from the carbon canister in the right front fender) with a piece of tubing and a 3/8" bolt and 2 clamps. Similarly, block off the other return line in the engine compartment (on the driver’s side coming out of the fender). Connect the carburetor to the metal line on the passenger side in the engine compartment. 

I have been told that if you have fuel pumps that are in the fuel tanks-- you can merely use the existing fuel supply system, or mount the new fuel pump (mechanical or electric) in line with the existing pumps.

Disclaimer: The information presented on this page is for personal use only. No responsibility is assumed by the publisher or anyone connected with it for loss or damages suffered through reliance on, or reference to, any information presented here. Use this information at your own risk.

Presented by Mark Chiampi on 9/27/97.


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