Fuel Relay or Something else

Finally got the 94 covert running good. While waiting for the final problem, a fuel pump relay, I had it jumped. New relay arrives and is installed and Bam. Car won’t start. Removed the relay and jumped it again and alls well. Tried the second new “spare” relay. same problem.

Tested and jumped the inertia switch with the relay in. No start. Grounds tightened and tested, fuse tested and still won’t start with a fuel pump relay installed.

What am I missing?

Does the o2 sensor come into play on this vehicle? Some need a signal form the o2 to energise the FP.

Interesting enough the XJ6 same year and engine has an O2 heater relay, But non of the electrical diagrams, or engine management diagrams show one for the XJS.
The only thing I can see from the electrical diagram of the engine management system is a feed from the EMS main relay. But if that was failing I should get more than the FF22 Fuel system DTC I’m getting without the relay in I would think.

Hello Charles - when you are placing the jumper wire, are you placing it in the relay socket pin holes - if you are, then I would be thinking that when you place the relay in to the relay socket, the relay pins are affecting the wire harness to relay socket pins such as causing an open circuit - what happens when you place the relay in to the socket, and then place the jumper wire at the outbound side of the relay socket pins at the harness connection?

I remover my jumper before putting the relay in. Not sure I could get them in with the relay as I’m using a spade connector jumper wire if that’s what you mean.

Hello Charles - okay - try using a wire jumper with no connectors on the end of the wire - try to place the ends of the jumper wire in to the “back side” of the relay socket, where the harness wire is connected to the relay socket - withe the relay out of the socket, test to see if the jumper wire is allowing the circuit to work causing the pump to run - now, place the relay in the socket, with the jumper still in place - theoretically, pump should still run since the jumper is still in place - now pull the jumper and see if the pump stops - supposedly it will, according to what you wrote before - this would indicate what I am saying - the relay pins are causing the open at the relay socket.

You don’t say which engine you have.
I had to run my 94 6.0 for six months with a jumped fuel pump.
No one could find why it died, until someone spent a few hours studying the schematic.
It turns out, the fuse for the heated O2 sensor was blown.
That prevented the fuel pump from running.
As I recall, it’s the #9 fuse in the boot.

I have the A6 engine. Tested that fuse and even replaced it to be sure. Im at the point now where Ill be checking the feed to pin 85 on the Relay that goes to pin 7 in the ECM Blue connector. Looks like Ive narrowed it to the ECM or the ECM relay. (I hope)

The Jag 4.0L Engine Management System Manual (S91) has pretty decent flow charts. I just forget to use them.

From what Ive completed following the Jag 4.0L Engine Management flow chart for DTC 22 I may not be getting a signal from the ECM. The power from the ECM relay is there in the WN wire at terminal 86. Making a connector to test pin 7 of the ECM which supplies power to pin 85 on the relay thru a NK colored wire. Your procedure will be a way to confirm that if I have no power from the ECM to pin 85 on the Fuel relay plug.

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Fuel pump control circuit failures are common – in the 6CU ECU for the early 80’s V12. Could it be that the later 4.0 suffers the same affliction?

On the V12, some owners simply jumper a wire to ground, allowing the relay to energize and run the fuel pump whenever the ignition is on. This is easy because the ECU simply provides a ground to energize the relay, you’re just bypassing the ECU there, the fuel pump is still powered through the relay and still requires ignition power to energize. The only reason the ECU is involved is for safety; if the ignition is on for more than 2 seconds without the engine running, it shuts off the fuel pump – presuming you’ve been in a crash or something. If you’re willing to forego that particular safety feature, a jumper costs considerably less than shipping the ECU off for repairs.

So, does the ECM for the 4.0 do the same thing for the same reason?

One of the last steps in the diagnostics flow chart.

the next step is try a good ECM

Yes, but the next step could be taken years later if you just leave that blue connector connected to ground.

That may be what Im doing. Made it thru the diagnostic for chart. Had voltage at the pin on the ECM leading to pin 85 on the fuel pump relay. When grounding it the fuel pump works with the relay in. On my car the the wire is pink with the brown tracer. There are a pair of diodes or resisters hooked into pins 85 and 86 external to the relay plug. My guess is one of them is not functioning.
Kirbert, Im guessing the lead from the ECU to pin needs to be grounded?

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You need to confirm with others more familiar with the 4.0.

Or just set up a trigger circuit and a load circuit and bench test the relay.

Wild card. Swap the FP relay with the horn relay.
Does the horn toot. Caveat, Ignition on…

Discovered the ground signal from the ECM is not making it to the relay socket. It’s present at the blue plug to the ECM. That leaves the ECM. I grounded that pin on the blue plug as per the diagnostics and the pump runs. Looks like the check engine light will stay on because the ECM needs a return signal it’s not getting.

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These are the two pages from the Jaguar 4.0L Engine Management manual

DTC22page 1.pdf (2.9 MB)
DTC22pg2.pdf (1.6 MB)

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Fuel Pump Relay.pdf (225.9 KB)

The items shown in the diagram as internal to the Fuel pump Relay are actually external. Can anyone tell me what the symbols stand for? Having trouble finding them online.

A resistor and a diode. The diode absorbs back EMF when power to the coil is disconnected. The resistor keeps it from absorbing too much.

Seriously doubt if those are external.

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What do the red and yellow wires go to coming out of the Fuel pump relay connector?