Fuel line routing in tank

I am new to Jaguars but have worked on and modified cars for over 40 years. Foreign and domestic. In the past I worked for a British care specialty shop in Colorado. So I am not a newbie to cars. I recently acquired a 1994 XJ12 that has not run in 3 or 4 years. It has 2 submerged fuel pumps. I have removed the tank, cleaned and am in the process of replacing pumps, strainers, fuel lines, pump retainers, and gauge sending unit. In other words everything in the tank will be new. My question is on the fuel line routing. Looking inside the tank the two inner lines are joined and the two outer lines are joined. Verified not only by sight but by using an air blower off of my compressor. I believe the two inner lines are pressure and the two outer are the return. If this is correct the two inner lines should go to the outlet of the pumps (the metal fitting) and the two outer should go to the plastic fitting on the fuel pump canisters. NOT the way they were when I took them apart. I would think that both outlets from the pumps should go together and the two returns (from engine) should go together. Does anyone know if my reasoning is correct.

Thanks

dldstrock

Deleted - duff information! :-0

I don’t know how the dual pump setup works but the brass fitting in Joe’s pic is the pump outlet for the canister …

HTH
http://www.jag-lovers.org/include/iv3.php3?zx=SdADygwIiM8ED8ZK%2FZfkxwTQDQOZnscKzAc41s2j3L1HN6OXyPgJPjSjzgpGB%2F4Bp4vIGLwLFN3dDQABOjWT0gVI%2FEtBlNUIObwLFNnU90IK%2FgCs2QQzBzhBy8cINf8%2BQJTW%2FkK9PDnZ09MJ%2BBIDlsjNCskJPp6czgvQUwefl8gFzwpGnJnGAscLAMeI0Q%3D%3D

Yes. Had that much figured out. Guess I will blow air from the fuel manifold on engine back to tank and see which one is pressure and which one is return on the bottom of the tank. The pumps HAVE to work in parallel or they would be fighting one another. Hook both brass fittings to the pressure side and the plastic fitting on the canister to the return side. Only way it can work.

dldstrock

Isn’t it easier than that? Doesn’t the feed line have the fuel filter in it just forward of the fuel tank? Bit of a problem comparing the 6 cyl and V12 fuel pump installations - the JDHT parts catalogue illustrations are incorrectly drawn/itemised for the V12!.

Yes, that is true. But I want to blow out all the junk in the fuel lines anyway. Finding accurate information on a v12 somewhat hard to come by. Most service manuals and parts manuals still showing my car to have the external fuel pumps which is not the case on this car. The build date is 4/93 but on the dealer invoice (have that too) 1993 is crossed out and 1994 written in. The car is titled as a 1994 also. So I believe the car is somewhat of a smorgasbord. Makes it interesting but kind of a pain in some instances too. The relays are not always in the stated places also. Oh well, I do not mind wiring and electrical either. Keeps the little grey cells percolating.

I don’t think external pumps were used after about 91 or 92, AFAIK later cars all had internal systems.

As Bryan said earlier, the diagram on JHT only shows a single pump, but you may get some benefit for other part numbers etc from the site anyway -

https://www.jaguarclassicparts.com/uk/jaguar-xj6-xj12-canada-usa-parts/air-and-fuel-delivery-systems/fuel-tank

Thanks for the web site. I am finding that by and large 94 data is more correct for my car than 93. So it seems it is more 94 than 93. I am curious though why it is inconsistent. Perhaps they ran out of certain parts and used later model parts in the build process. Probably will never know but I find it interesting.

You can determine the MY (i.e the build standards) by VIN. I do not think there is any significant difference between the 93 and 94 MY specifications. Be careful of that parts catalogue picture for the 6.0 litre V12 - note that they show TWO return pipes at the pump and no feed pipes! :slight_smile:

The XJ40 V12 was introduced in the '93 MY at VIN 673299 (known as the “1993.25 MY”)
The 1994 MY ran from VIN 687219 to VIN 708757

If you send me your e-mail address I have found a picture of the dual fuel pump installation which I can send as a pdf file attachment to a PM.

As Bryan just said, forget going by the year with these cars.

You can only go by the VIN number.

In my case that’s not consistent either. My VIN is 681783. There is a very nice older gentleman in the parts department at my local Jaguar dealer that is very helpful. As the dealer no longer has many parts for the car he is willing to look things up and get me a part number. And, for instance, my car should not have dual pumps, although it does. As this is not my daily driver and never will be, I take parts out and look at the part number to make sure I am getting the right thing. I know the past history of the car and believe it to be unmolested. The original buyer was J.B. Hunt of Hunt trucking. He sold the car to a relative and my neighbor across the street bought it from him in 1999. He saved all his maintenance receipts so I have a good idea of condition. I bought it from the neighbor, so the 4th owner. The car is very solid though needs paint also. I am enjoying figuring it out and bringing it back to life.

P.S. email dstrock90@sbcglobal.net

That is a late '93 MY XJ40.

PM sent with PDF of fuel pumps attached

Why shouldn’t it? Because the parts diagram shows only one? :roll_eyes:

The XJ81 was (is) fitted with twin pumps so your car is quite “normal” AFAIK.

Ok. Tank back in car. No start. Cranks no start. If I hot wire the pumps at the black two wire connection plugs they run. I have installed a clear hose to the return fitting off of the fuel manifold to verify having fuel to engine. So started back tracking from the two black connectors. When I jump the fuel pump relay I get power to one pump. The pump that has the blue wire with red tracer. The other pump does not get power. It has a solid red wire. That wire goes to a large (80mm by 15 mm) black rectangular plug located on the right side of the care behind the transmission control module. It has holes for 20 wires,17 which are filled with wires. I also suspect that I am not getting power to the ignition system but one thing at a time. What controls the one pump with the red wire? I am using a 93 xj6 wiring diagram. I know, I know, but presently its all I have. Please take into consideration I am just getting started here. The xj6 only shows the one pump and it is controlled by the pump relay. Does the ignition relay control the one pump and the ignition? If so that is probably my problem. Thanks for all you help so far. dldstrock

The two fuel pumps on a V12 are identified as ‘A’ and ‘B’

Pump ‘A’ is the primary pump for engine start and running, Only when the engine reaches 2840 RPM is the secondary pump ‘B’ switched on and it remains on until the engine RPM drops below 2000 RPM. Pump ‘A’ runs continuously throughout.

The pumps are activated by separate relays and the secondary pump ‘B’ is controlled via the fuel pump control module which is fed engine RPM data via the Ignition ECM.

The positive feed to pump ‘A’ is on a Blue/red wire from its relay and goes to ground via a Black wire.
The positive feed for pump ‘B’ is on a Red wire from its relay, again going to ground via a Black wire.

Both fuel pump relays are fed power from the Fuel Injection ECM via the Oxy sensor Heater relay.

Thank you for the information I have tested all but the ignition on relay. The oxygen sensor relay is good. The EMS relay is good. The fuel pump relay is good. The car will not light off even with some carb spray shot into the intakes so the ignition relay is suspect, I believe. I understand it is under the center console. Sigh. What a place to put it. I will go after it Sunday or Monday. Supposed to rain Friday and Saturday. Garage is full at this time and I need it to run so I can swap things around and get it into the garage. Right now in driveway next to garage door. Too stinking heavy to push. Need it to run. Plus just want to hear it run.

Thanks again for all your help. I really appreciate it.

Dan T.

P.S. Is it possible to test the operation of pump B by raising the rpm of the engine in park or does it also need a speed sensor input from the transmission? Also what is the location of pump B’s relay? I have been cleaning all contacts I come across (including all fuses) and spraying them with DeoxIT D5. The grounds I come across I clean and apply DC4 which is a dielectric grease.

dldstrock

The relay for fuel pump ‘B’ is in ‘Relay Module L’ the one with the black base in the front right corner of the trunk. (Next to Relay Module K with the blue base inboard of ‘L’).
The fuel pump control module is just forward of the relay in that position.

The relay for pump ‘A’ is the regular one in the right rear corner of the trunk, also with a black base.

I see no reference to a requirement to achieve a given road speed to activate pump B after 2840 engine RPM

As a matter of interest, do you have a spark at the plugs and are they drenched with fuel after failed attempts to start it?