My 98 XJR will not start. Cranks fine but no combustion. Suspected its not getting fuel and i was right. Got a fuel gage and tested the fuel pressure at the fuel rail with the key in the ON position. 0Psi.


So now im trying to verify that the fuel pump is getting power. I don't know what wire to test the voltage at though.

This is one wire that goes to the top of the tank and it gets 12v on the blue/white wire. But nothing on the others.



Here is another wire that goes to the top of the tank. It did not lite up the test light ever.


Is the blue/white wire the one that powers the fuel pump? Should i get voltage on any of the other wires?

Thanks,

 

PS i am using this thread for my reference material so far:
https://www.jaguarforums.com/forum/s...ad.php?t=10157

 

Supercharged XJs have 2 fuel pumps.
Pull one or both of the fuel pump relays(#1 and #4) and jump the 30/87 terminals of the relay board and you will have power to the pump(s) until you remove the jumper (if the fuse and wiring are good). If you have positive and earth to the connector on the EVAP flange on top of the tank then the fault is in the tank (poor connection or faulty pump(s). Power + is on wires brown/blue and blue/red. Black is earth/ground.

bob gauff

 

Thanks alot!! brown/blue and blue/red did not light up my test light. Ill check again tomorrow. But this is good news. I would rather replace a relay than drop a full tank of gas.

Alldata says to replace relays between R6K1 and R6K8... Is this a factory defect in the relays? Mine are all R6K4 so i guess they all need replacing.

Are both of the pumps in the tank and are both the same model?

Other links i want to list just for my own benefit are:
Thread talking about jumping the relays:
https://www.jaguarforums.com/forum/s...ad.php?t=31160

Site warning about after market fuel pumps:
http://www.autohausaz.com/jaguar-aut...uel-pumps.html

 

I jumped both the relays, verified getting power X 2 and ground X 2 at the wiring harness where it connects to the EVAP flange. I connected the harness while it was jumped, still no fuel pressure at the rail, tried starting the car, would not start. Did not hear the fuel pumps turn on when i plugged the harness into them.

So now i am trying to figure out if i have bad relays, bad pumps or both.

These relays dont seem to work like the ones i am familiar with (starter relay). I have identified the constant (+), key on (+) and the drain (going to the fuel pump) but am mystified by the fourth plug. I was expecting it to be a ground and it is not. Im i loosing my mind here?

I assume if i jumped the relays and still got no fuel pressure that both pumps are dead?

 

Read up a little more about the relays and figured out what the extra thing on them was. Its a transient suppressor in parallel with the switch. Reduces voltage spikes when the magnetic field of the relay breaks down. So in short its a normal relay to you and me.

Some of the relays get a hot applied to one side of the electromagnet and some to the other. So i guess the relay does not discriminate on polarity operating the magnet.

One half of the magnet gets 12v when i turn the key on. I thought that this was the trigger last night. But i have a new theory. Yes the magnet gets 12v when the key is on, but to throw it needs a ground also. I get 19K ohms (Thats no ground people) where i need that ground. Thats why its not switching. The switch is not bad its the input to the switch.

Now i remembered reading a few days ago that the fuel pumps will only run for 2 seconds when the car is about to start. I assumed that was because they built up enough pressure. But i now think its a timer built into the ECU.
Reference post 3:
https://www.jaguarforums.com/forum/s...ad.php?t=10157

So if i am right the REAL trigger is the grounding of the other electro magnet post. I bet the computer only does this for 2 seconds. Short enough time for me never to see the ground by the time i get to the back of the car.

So i should be able to pull fuses 7 or 15 and hook up a test light to where the fuse plugs in. Then have a helper turn the key on. Now i am still going to have to guess which side of the fuse slot to plug into. But that will only take 2 times.

 

Used the method of disconnecting the battery and reconnecting the battery with the key on to avoid needing a helper. Yes i was right. It only gets power to the pump for 1 second.

also special note for XJR owners!!!
Only one pump gets power at key on. Its the pump that goes through relay 15.

Looks like im replacing the pumps. On the upside i no longer think i have lost my mind.

 

I think the pump that runs at key-on is pump #2, the high-speed pump. When my pump #1 died, the car would reliably start (fuel system pressurized with working #2) then die at after a few seconds at idle (normal operation with #1).

So it looks something like this?

Key-on, initial fuel rail pressurization --> pump #2
All other times, engine running --> pump #1
Engine speed over 3000rpm --> pump #2 comes back on in parallel with #1

TTYL
David

 

And when youre replacing both pumps, carefully check for black burned connectors in the tank and the evap loss cap you take off to access. The burning doesnt make the pumps go bad, but the pumps pulling too many amps burn the conectors. Replace them if they show any signs