I have a 95 XJS V12 convertible with only 8K miles, but the other day it was idling and shut off. It turns over fine, but i am not getting any fuel. I dont hear the fuel pumps kick on when I turn on the key. I disconnect the fuel lines at the engine and I am not getting fuel from either line. I checked both fuel pump fuses and they are good. I tried resetting the inertia switch in the passenger door jamb area and that did not make a difference either. Any idea what the next step would be? I dont think that both fuel pumps went bad at the same time. What else could cause this problem?

 

Test for 12v at the pump live wire. If none; test the fuel pump relay.

 

From what i have read, this vehicle has two fuel pumps mounted in the gas tank. Do i need to pull the tank to be able to test for 12v at the pump?

 

Sounds like it is probably either a clogged fuel line or filter.
When was the last time the filter was changed?
FIRST. Disconnect the filter under the front left wheel well and capture what comes out.
Always use a large CLEAN container to capture the fuel.
Inspect the quality of the fuel.
Yes, there are two fuel pumps inside the tank, and getting at them is a PITA.
Pull the vacuum line that goes to the fuel pressure regulator.
FIRST Check to see if there is fuel in the vacuum line.
If there is you need a new FPR.
If not, determine if you are getting vacuum to the FPR.
After doing all that then we can look into fuel lines IN the tank.
When I pulled the tank in my 94 I found all the lines had loose clamps.

 

if it was just a clogged line or filter i would assume i would still hear the pumps run when i first turn on the ignition. I don't hear anything when i turn the ignition on.

 

I misread your post about NOT hearing the fuel pumps.
Closely examine the black connector that goes to the tank behind the panel.
The often get heated up to the point of melting the plastic connector and the wire insulation.
Disconnect it and jump 12 volts to it and see if it runs the pump.
If the pump runs, check the Heated O2 sensor fuse in the boot.
Probably behind the panel on the right side.

 

If this is the connection you are referring to, i tried putting 12v on it and nothing happened.

 

Hi Todtz1

That is the Fuel Gauge Sender and I wouldn't mess about with that if I were you as if you undid that Locking Ring you would be swamped in Petrol that could burn not just your Car but also your House and Garage down, especially with that Battery being so close

So please just be aware of that and be Careful!

As for replacing the Fuel Pumps, you may not have to do that and lets hope not, as removing that Tank and the In-Tank Fuel Pumps is 'The Job From Hell' especially on a Convertible, where a 'Shop' may want to Charge an incredible $3,000 'Yes! Three Thousand Dollars' to do that Job for you

There is quite a High Possibility that your problem Could either be The Crank Position Sensor (although I'm not sure if your Car has got one of those) or it could be the Fuel Pump Relay or the Main Relay or both (as the Fuel Pump Relay will not work without the Main Relay)

So when you Consider that Fuel Pump Relays only Cost a few dollars, I would go and get one and see if that makes any difference

Although before you do any of that 'Better Call Paul (ptjs)'' who will be able to tell you if your Car has a CPS Crank Position Sensor, as although I have an XJS V12 I am not familiar with the V12 6Litre Set up

 

Todtz1,

As you probably know, you have 2 Fuel pumps but they operate at different times.

When the ignition is switched on (position II), the ECM initially switches on fuel pump 2, after a delay of 0.1 second. If the ignition switch remains in position II without moving the key to crank (position III), the ECM will switch off pump 2 after a maximum of 3 seconds.

When the ignition switch is moved to crank (position III), fuel pump 2 is switched off and fuel pump 1 is activated. Fuel pump 1 operates continuously while the engine is running. The ECM activates pump 2 at higher engine speeds to provide increased fuel flow during high engine demand.

As you've checked the Fuel Pump fuses, start by checking the current output to the pumps from both of the Fuel Pump Relays. Check Relay 2 immediately on turning on ignition. Then check Relay 1 on engine cranking.

Good luck

Paul

 

As the others have said, that is the fuel level sensor.
What I was talking about is the fuel pump power connector.
It's behind the same panel but the harness is mounted along the pinch weld of the tank.
There are four wires and the plastic connector is black.

 

:
I think you have a few details a bit off on the dual fuel pump setup though not by far. Essentially this FP1 used for priming and engine start/low speed is handled by the ECU's control over FPRelay1. FP2's running is entirely dependent on the engine RPM as a signal from the Marelli ECU, and interpreted by the Fuel Pump (2) control module which controls FPRelay2, and thus Fuel Pump 2. The fuel ECU is not involved in that decision.

With all 6, 16, 26, and 36CU series ecus, they have initiated grounding of FPR1 with key-on (priming the system). By the 36CU the +12V from the starter signal had been eliminated and it relied entirely on the RPM signal to restart FP1.

The Fuel Pump 2 Control Module is entirely separate and independent from the Fueling ECM and makes it's decision based on RPM input alone: AFAIK it does not engage FPR2/FP2 with power on, then disengage, then wait for a 2840RPM pulse from the Marelli ecu to re-engage. It only engages (AFAIK) with that RPM count. I could be wrong, but I'm almost dead certain that the 36CU acts the way all ECUs in it's line did, and does the key-on FPRelay grounding for a few seconds..







It's worth also noting that the fuel tank was revised for 1995 to contain the two fuel pumps in the same swirl pot - presumably reduced part count and made servicing slightly easier.





~Paul K.

 

Ferrari Guy,

Great! Tks for that! I've just found similar in the Jaguar training manual.

I couldn't find the Lucas / Marelli bit earlier so was just quoting from the Nippon Denso training material as fitted to the late saloon cars. That's where it stated that Pump 2 runs on ignition pos II and at high revs, but Pump 1 does cranking. See below:



So I'm guessing that because Fuel Pump 2 isn't controlled by the ECM on the XJS installation (unlike the ND installation) , therefore the Ign Pos II priming would be activated by Fuel Pump 1, rather than Fuel Pump 2?

Cheers

Paul

 

Oh nice bit of trivia on the workings of the Nippondenso ECU! Thanks!

The whole CU series has been an evolution. Key on energizes the main relay, which sends power to the ECU. As part of it's wake up routine, it provides a ground for the FPRelay for a few moments, and then stops unless it gets a further signal. Up until the 16CU it has both the +12V from the starter relay on pin 26, and the speed pulse on pin 18. The 26 and 36CU ECUs were really just derivative upgrades from the 16CU but with a few pinout changes (and emission and a bit of early diagnostics added). Those elimited the starter signal input and only used the engine speed input for restart of the fuel pump.

Technically I believe it MIGH be possible to use a later 26/36CU on an earlier car IF one was to re-arrange the pinout on the connector but no one has as of yet tried that, and there would probably be some limits as one would want to only try this with engines of the same displacement, which limites how far back one could swap without an EPROM change from someone like R Bywater.







~Paul K.

 

Is it one of the wires in these photos that i need to put 12 volts on to test the fuel pump? Also, is the black rubber hose in the photo supposed to be attached to anything? it was just laying loose under the battery tray.

black rubber hose comes out of floor and other end is not attached to anything(top left of picture)

image of battery tray with battery removed

 

Can't speak to testing the fuel pump, but the hose you indicate is I think for the battery vent; you can expect a number of comments on whether it's required these days, or not😁

 

todtz1,

If you can't find the pump connection, bridge terminals 30 to 87 on the Pump Relay with ign on and the pump will run,

Paul

 

That hose is the battery drain hose.
The harness I was telling you about is very near the TOP of the tank.
It originates from behind the brace along the right side of the boot and terminates on the top of the tank.
It's normally clipped to the pinch weld along the tank.

 

 

Wow, I got sick of waiting for him to get to the point so I fast forward to his "diagnostics"
He is obviously not such a great mechanic since he can't even resolve a simple fuel sensor leak.
Also he recently replaced at least one pump and did not know that only one pump runs at startup.
If he ran 12 v to the connector he wouldn't have to do all the other crap.
This guy is going to kill himself putting any fuel related parts in an ultrasonic cleaner.
DON'T LISTEN TO ANYTHING HE HAS TO SAY!!!!!!!!!!