Fuel tank switch problem

XJ
21

The fuel relay just connects the white wire to the white/green that connects to the fuel pump.

Relay is readily available and is easily bypassed. Just jumpwire between white and white/green - the pump will run whenever the key is to ‘run’.

There is a fuel safety devise installed, a reed switch in the AFM. In ‘crank’ this devise is bypassed, and the pump will run. But with ign key to ‘run’, the reed switch will not activate the fuel relay unless the engine is running.

Typically, with a failed reed switch input the engine will start, but as the pump is not running engine will stop as it runs out of fuel. Again, easily bypassed by connecting white to white/green…

Do that, and see what happens…

Frank
xj6 85 Sov Europe (UK/NZ)

22

Sounds easy! Will try that! Many thanks, this is a really useful forum! Cheers!

23

Now I got confused…this scheme indicates that the fuel pump relay is the one with #2, but in the Haynes manual (yes, I know it has a bad reputation…) it says it is #1…I removed #1 to depressurize the system before replacing the changeover valve. Could this explain why the engine does not start now?
graphic

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Look at the wiring colours… refer to BS-AU7

25

But the diagram shown is correct, Maiato - whatever the Haynes manual otherwise says.

What you did, removing the main relay and replacing the changeover valve, should have no effect on engine starting and running when the components are in place and working correctly…

We’re back to my original suggestions verifying that the pump works and pressurizes the system - including jumpwiring fuel relay. Verify fuel relay colors as David suggests to make sure…

Frank
xj6 85 Sov Europe (UK/NZ)

1 Like
26

Before jumpwiring any cables, I removed both main and pump relays and tested them with the help of a 12V battery and a multimeter and they were both just fine. However, when I checked voltage at the relay docking (where all the wires end), I had aprox. 3.5V in the pump relay docking, and aprox. 10.5V in the main relay docking. This suggests that the reason for failure to start the engine is likely to be in the wiring system that ends at the docking and does not convey the necessary voltage to the relay. Any ideas where to look at?

27

There is power only to one wire on each relay, Maiato…

Fuel relay; white wire (ign on). Main relay;brown wire (always powered). Both measured to ground - and should show battery voltage. Other measurement points may show stray voltages - of no relevance to voltage feed.

Relays’ only purpose is to connect these ‘in’ voltages to the relevant ‘out’ wiring. There are some pitfalls in testing relay functions with multimeters; relays may click but still may fail to connect properly - a test lamp is preferable. Or jumpwire the sockets to bypass the relays - to see if things work then…

Basically, if the pump runs and the injectors click while cranking; the relays do what they are supposed to do - and non-start has some other ccause…

Frank
xj6 85 Sov Europe (UK/NZ)

1 Like
28

Frank Andersen, I owe you a good bottle of wine! I finally had a chance to jumpwire the white with white/green wires in the fuel relay and the engine started like a champ! I could immediately hear the fuel pump running with just ignition on and the switch valve is also now working perfectly fine. Great feeling to have done it all with my own hands! If you ever come to Portugal…:wink:

29

You did the work, Maiato - the kudos are all yours!..:slight_smile:

This implies a faulty relay - have you tried replacing it?

Frank
xj6 85 Sov Europe (UK/NZ)

30

I ordered a new one. I am just not sure whether the fault is on the relay, or in the socket. I tried to find a replacement for the socket, but unsuccessfully. Any ideas where I can get one online? Onve again, many thanks for the great suggestions!

31

The socket is a generic SPDT relay socket.
If it’s not melted it’s ok.
Remove the female connectors from the socket and bend them to be sure they make good contact.

32

Unless visibly damaged; it’s unlikely to be a faulty socket, Maiato - more likely the relay…or…

As mentioned before; the fuel relay is part of the fuel safety circuit. In ‘crank’ the relay is operated from ign switch through the red diode pack. In ‘run’ the relay is powered via the diode pack from the reed switch within the AFM - only if the engine is drawing air/running.

If the reed switch or diode pack fails, the engine may start in ‘crank’, but as the key is released to ‘run’ the fuel pump stops - and the engine dies…

Frank
xj6 85 Sov Europe (UK/NZ)

33

Helder,
During my past 22 years of Jaguar XJ6, XJ12, and XJ-S ownership I have had several of those plastic relay sockets located in the engine bay break and crumple in my hands due to the engine bay heat and age.

20221128_112732
20221128_1127321920×1440 272 KB

I recently removed several very nice looking plastic sockets in a variety of colors (see attached picture) from a 1985 XJ6 Vanden Plas that was at a local junkyard. Fortunately for me, Jaguar used the same type of “RISTS” plastic sockets throughout their cars and the ones that I removed from inside the dash were in excellent shape.
Do you have any “Pull Your Own Parts” junkyards in Portugal or know anyone that has a Jaguar XJ6 or XJ-S parts car? I have had good luck keeping my Jaguars running with parts that I have harvested from parts cars. Perhaps this is an option for you if you can not find new ones online?
If your plastic socket is indeed broken and the cause of your problem, and if you are unable to find one locally, send me a Private Message through Jag-Lovers and I am sure that we can work something out for one of these used ones that I have.

Paul

1 Like
34

Dear Paul,

this is very kind of you. I think I managed to order new sockets from China. They will arrive only by the end of January and should do the trick. In the meantime I will receive the new relay in few days and see if it solves the problem. I will let you know in case I fall short of one of those plastic sockets. Unfortunately there are not many of those Jags in junkyards around, but those would have been a good source of parts indeed!

Many thanks once again and best regards,

Helder

1 Like
35

Hello guys, I think I am back to stage 1…after ordering a new relay to replace the faulty one and replacing also the metal connectors on the white and white/green wires (the old connectors broke when I removed the wires from the socket to jumpwire the relay…) the car started and ran great for few days. However, one day the car just didn’t start at all. I thought it was some bad connection (I found that the metal connectors often got loose from the wires in the socket), so I tried to jumpstart the white with white/green wires bypassing the relay as before, but now I can’t start the engine. I can hear the pumps working in the back, but no start. Battery seems to be fine. Any ideas?

Before all this saga started, whenever I tried to restart the engine while it was hot, it wouldn’t start at first attempt (it always started at first when engine was cold :-)), with no signs of fuel injection, with very similar symptoms as I get now. Don’t know if this is related with what I am facing now?

Last, but not least, does anyone have a wire scheme/photo of the starter relay? I found a loose wire while I was working on the pump relay (might have pulled it inadvertently). I put it back in place where I think it was, but I am not 100% sure.

Thanks a lot and apologies for my poor knowledge!

Helder

36

Crank but no start or the starter doesn’t work?

37

[quote=“Helder_Maiato, post:35, topic:426812, full:true”]
Hello guys, I think I am back to stage 1…after ordering a new relay to replace the faulty one and replacing also the metal connectors on the white and white/green wires (the old connectors broke when I removed the wires from the socket to jumpwire the relay…) the car started and ran great for few days. However, one day the car just didn’t start at all. I thought it was some bad connection (I found that the metal connectors often got loose from the wires in the socket), so I tried to

jumpstart the white with white/green wires bypassing the relay as before, but now I can’t start the engine. I can hear the pumps working in the back, but no start.
[unquote]

If the fuel pump then runs. Helder; the relay/socket has no bearing on a non-start. I assume the engine is cranking (since you also mention the starter relay)?

[quote]
Before all this saga started, whenever I tried to restart the engine while it was hot, it wouldn’t start at first attempt (it always started at first when engine was cold :-)), with no signs of fuel injection, with very similar symptoms as I get now.
[unquote]

‘…no sign of fuel injection’ - do you mean the injectors are not clicking while cranking?

The injectors are triggered by the ign amplifier - white/black wire connected to coil ‘-’. No injector action; no start - have you checked if a spare plug will spark? Are you sure there is no injector action??

Differences between cold and hot starting is a separate symptom - no hot start may imply an ign amp problem, as said.

Connect a test lamp between coil ‘-’ and ground. With ign ‘on’ the lamp should be fully lit - while cranking the lamp should dim and flicker…

[quote]
…diagram of the starter relay.
I found a loose wire while I was working on the pump relay (might have pulled it inadvertently). I put it back in place where I think it was, but I am not 100% sure.
[unquote]

There are no white wires on the starter relay - if the engine cranks there is nothing wrong with the starter relay…

A white wire gives power to the pump via the pump relay - so the white connection at the relay socket is 100% important…

We’re here to add to your knowledge, Helder…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

38

the engine doesn’t crank…(sorry for my poor terminology)

39

sorry again for my poor terminology…the engine is not cranking at all.

When I refer to the loose wire in the starter relay, it was a white/red wire.

Question: in crank position, should I get any read in the battery monitor? (just checking…)

40

The starter relay just connects relay red/white to relay brown (battery power) in ‘crank’, Helder. Use a jumpwire to connect red/white to battery - if the engine then cranks; your relay/connections is the problem…

Crudely, if the relay ‘clicks’ when when turning key to ‘crank’, relay is responding. If there then is one or two vacant terminals on the relay that fits the white/reds connector - that’s where it goes. As a start…:slight_smile:

There might be more to it, but try those first - to see what happens…

Frank
xj6 86 Sov Europe (UK/NZ)