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Last weekend my 1994 XJ6 stopped running on a trip to the grocery store.
I finally got around to diagnosing the problem today and discovered that there was no power to the NY wire leading to the fuel pump relay socket.
After examining the wiring diagrams I went back to the right hand fuse box and discovered that the 25A C6 fuse in the right hand fuse box that supplies power to the fuel pump relay was blown.
I replaced the fuse and then tried starting the car. It started and ran for 30 - 60 seconds and then died again.
Upon checking the 25A C6 fuse again I found that once again it was blown.
What could cause this 25A C6 fuse to blow this quickly?
If I jump power from the battery to the blue w/red wire in the fuel pump relay socket I can here the fuel pump running.
It sounds normal when I do this.
This is my daily driver and I have been crippled by it being out of service these past few days.
I cleaned the grounds at the right rear corner of the trunk and tried another fuse.
This time the fuse blew as soon as I turned the key on.
I actually heard it go "crack" from the driver's seat when I turned the key.
The pumps can draw too much current when the filter gets clogged? (or just a worn-out pump)
The electrical connector pins in the EVAP FLANGE on the tank top get burnt from the excessive current draw.
I would replace the filter and check the current draw across the relay 3/5 or 30/87 terminals.
On the '93-'94 cars, there is an electrical connector behind (technically in front of) the battery that is in the harness for the fuel pump. On our '93, this connector arced and burned and caused a sudden cranks-but-won't-start condition. It would be worth having a look at that connector. It's behind the carpeted trim panel for the fuel tank, so you have to remove the spare wheel, jack, etc. to pull that panel out. I think I have photos of the connector in my Jag-Lovers album at the link in my signature.
The link harness should also have a noise suppressor module built into the wiring. I have also had to replace one of those because of burnt pins.
On our '93, the module Bob mentions was just a Zener diode and capacitor connected across the two wires to the fuel pump with crimp connectors. They were a few inches down from the connector at the evaporative flange, covered in heavy heat-shrink tubing. When the diode and capacitor failed on our '93, one of the devices, probably the diode, created a dead short. I guessed at their values and ordered replacements from Mouser. They're not strictly necessary, but without them the fuel pump will probably cause electromagnetic interference that will cause static in your radio reception, especially since the fuel pump is so close to the radio antenna and the fuel pump and antenna motor even share the same ground point.
Today I did some more tests on the car. I removed the fuel filter but it was not clogged up. I replaced it anyway.
I also tried another blue four pin Jaguar relay but this made no difference.
Then I did some more tests but still when I turn the key on with a fuse in the C6 fuse position and the original power & ground wire connected to the socket on the top of the tank to power the fuel pump, the fuse immediately blows. If I have the socket on top of the tank unplugged the fuse does not blow when the key is turned on. I did disconnect the battery and remove the fuse and relay from the relay socket, and checked both ends of the NY wire (at the relay socket and at the fuse box) with an ohm meter to see if it was shorted to ground but this does not seem to be the case.
So as a test I wired up an inline fuse and another relay direct to the positive post on the battery.
I powered pin 30 of this temporary relay direct from the battery through an inline 25A fuse.
Pin 87, the output of the relay is jumpered to the original relay socket where pin 87 of the relay would normally plug into to supply power to the rest of the fuel pump circuit.
The two wires for the control circuit of the temporary relay, pins 85 and 86, are also connected into the original relay socket in the corresponding socket plugs.
inline fuse and relay wired direct to battery Output of temporary relay wired to output socket of the original relay socket to feed power to the pump. Control circuit wires also connected to corresponding socket plugs in the original relay socket.
The battery was too dead to try starting it. I was able to turn the ignition key to the on position several times and each time I heard the fuel pump run for a second or two without blowing the 25A fuse I put in the inline fuse holder. I have the battery charging overnight and I will try it tomorrow morning.
This makes no sense. With the fuel pump wired up in this jury-rigged wiring as shown in the pictures above, the car runs. I had to use starting fluid to get it to fire off, possibly because of air in the lines after changing the fuel filter but it runs and seems to start just fine now. I don't get it. Could the wiring running from the C6 fuse in the fuse box down at the passenger's feet back to the rear corner of the car just have too much resistance somewhere? I checked it for a dead short at both ends of the wire but I have not actually used the ohm meter to read the resistance of the whole wire.
This makes no sense. With the fuel pump wired up in this jury-rigged wiring as shown in the pictures above, the car runs. I had to use starting fluid to get it to fire off, possibly because of air in the lines after changing the fuel filter but it runs and seems to start just fine now. I don't get it. Could the wiring running from the C6 fuse in the fuse box down at the passenger's feet back to the rear corner of the car just have too much resistance somewhere? I checked it for a dead short at both ends of the wire but I have not actually used the ohm meter to read the resistance of the whole wire.
One possibility that comes to mind is a problem inside the fusebox itself, but usually that is cracked solder joints that need to be reflowed/supplemented.
Another thought that comes to mind is that in the '93-'94 cars the oxygen sensor heater relay is in the circuit of the fuel pump relay. Worth checking out.
I just checked the MY93 wiring diagram and it says that the power for the NK wire going to the O2 sensor heater relay is run from fuse C4, and that nothing else other than the fuel pump uses C6. C6 which supplies power to the NY wire is the only fuse that is blowing. The C4 fuse is fine.
Drove the car on a 15 - 20 minute errand trip to the local pick-n-pull junk yard to pickup a used battery for the car and a good used tire for the blue 1988 car.
The car ran there and back just fine. This is still with the jury-rigged wiring as shown in the pictures in the previous posts to this thread.
If the fuel filter was clogged, chances are the pump may well be too. There’s a mesh filter under/ over another screen filter into the pump.
you didn’t show a pic/ say what kind of matter was clogging the filter, but if it’s rust, then it’s trouble. You almost certainly will need a new pump, and possibly a tank. (Or a way to clean / derust the tank).
The fuel filter was not clogged. After I removed the filter I was able to blow through it just fine so no blockage. I put a new one on anyway because I have no idea when it was last changed.
04-14-2021, 05:09 PM
Blowing 25A C6 fuel pump fuse
