fuel gauge D2

[Geoff]

Hi All, I need a bit of help as I cant get my copy of RAVE to work.


the other day I pulled a 7 core wire through the passenger side bulkhead. since I did this (so I am assuming that it is a result of a damaged wire or something) my fuel gauge has been all over the shop. most of the time it is off the scale showing no fuel (fuel light on) but other times it will show anything from 1 bar to the actual fuel level. I have checked the wiring at the sender and this seems OK.


my question is... does the fuel sender wiring go through the bulkhead to the BCU and if so, what colour wire is it?


any other suggestions would be great


Thanks - Geoff

[Pippin]

Hi Geoff,
It may be that your sender unit has detached itself from the pump and is floating around attached only by it's 2 wires. The unit slides up in it's location and clips in place. I have had this problem of random readings for 6 months thinking it was an electrical problem that I was unable to trace. Finally removing the pump to replace the sender unit I found the problem and just relocated it and clicked it into place, problem solved.
Nick

[Pinelli]

X2 detached sender unit.

I had this exact problem with the same symptoms.

[sierrafery]

my question is... does the fuel sender wiring go through the bulkhead to the BCU and if so, what colour wire is it?





Thanks - Geoff

Hi, to answer your question: Yes it goes through the bulkhead but not to the BCU, from tank it goes to C0378(that grey roundish 14 pin plug near the fusebox) and from there it goes to a plug under the steering wheel(C0047) and up to the instrument pack(no connection with BCU), the wires from sender are pink/black and green/black

[Geoff]

thanks guys, I will check the sender. how do you get it out from the top of the tank?

[Pippin]

Hi Geoff,


This link is very helpful TD5 Disco Fuel pump/sender unit - Land Rover Technical Archive - LR4x4 - The Land Rover Forum (http://forums.lr4x4.com/index.php'showtopic=54796) with pictures. I now avoid high delivery fuel bowsers.


Good luck
Nick

[Geoff]

Hi Geoff,


This link is very helpful TD5 Disco Fuel pump/sender unit - Land Rover Technical Archive - LR4x4 - The Land Rover Forum (http://forums.lr4x4.com/index.php'showtopic=54796) with pictures. I now avoid high delivery fuel bowsers.


Good luck
Nick



awesome, thanks

[Pedro_The_Swift]

would this be a good time for the lad to check on chafing fuel lines??

[Pippin]

Yes, definitely a good time to check for chaffing, but be very careful not to contaminate the fuel connections to the pump. There are some good recent threads on this chaffing issue. However I must admit to not having checked mine, but at 410K I presume there is not a weld issue down there, but I will get under there and check it out when I have time, it makes sense.
Nick

[PeterM]

Slight digression here gents but is the sender an older type with a float on a wire?

The reason I ask is because my gauge is rather pessimistic, as in the fuel light comes on with about 35L still in the tank. Can this be adjusted and if so, how?

[Outback 1]

they are a float on a wire but the most likely reason for your issue is the contact arm not touching or the slide it runs against is badly worn

[PeterM]

The gauge reads through its full arc without issue, just that it is incorrect.

Looks like a bit of wire bending is in my future ...

[Geoff]

Ok, checked the sender unit on the pump and it is all attached and the connections are good.


I plugged the sender in while it was out and tried moving the arm to see if the gauge moved but to no avail.


Can I short the wires at the connector to see if the problem is in the sender unit?

[Pippin]

Hi Geoff,
Sorry to hear that it was not caused by a detached sender. "The sender unit comprises of a rotary potentiometer supplied with a voltage of 5.0V from the instrument pack. The output voltage from the potentiometer varies according to the resistance through the potentiometer in relation to the fuel level. The output voltage is connected to the fuel gauge in the instrument pack. The fuel gauge receives a battery voltage input and this is compared with the output voltage of the potentiometer. The difference between the voltages determines the deflection of the fuel gauge pointer." This is from the manual. You should check with a multimeter that you have the 5V at the sender and a varying voltage from it's output when you move the float arm. It may be that the sender is faulty, do this test first and we can take it from there.
Nick

[Pippin]

Geoff,


If you do not have access to a multimeter shorting the sender wires will show a full tank on the gauge but be very careful if you do this.


Nick

[Outback 1]

when you get the time I have a working one here we can plug into it

[Geoff]

ok, some results. I think I will take you up on your offer Ken.


1. disconnected the electrical plug at the sender/pump unit, put the multimeter across the sender pins = open circuit (with tank 3/4 full)


2. shorted the pins = no movement on the fuel gauge.


3. shorted the pins at the under bonnet fuse box and when I turned on the ignition on, the gauge showed full then dropped back to empty


4. shorted the pins on the other side of the connector at the fuse box and measured continuity at the sender unit plug = 0.6 ohms resistance so the wires are intact.


5. checked continuity between sender wires and ground = pink wire is ground


6. tried again shorting the pins at the sender unit, this time with a paperclip (like in step 2) and when I turned on the ignition on, the gauge showed full then dropped back to empty


this leads me to believe the sender is faulty


what do you think, is the pink wire supposed to be ground?


cheers

[sierrafery]

...what do you think, is the pink wire supposed to be ground?


cheers

Yes it is

[Pippin]

Hi Geoff,
Sorry to hear that it was not caused by a detached sender. "The sender unit comprises of a rotary potentiometer supplied with a voltage of 5.0V from the instrument pack. The output voltage from the potentiometer varies according to the resistance through the potentiometer in relation to the fuel level. The output voltage is connected to the fuel gauge in the instrument pack. The fuel gauge receives a battery voltage input and this is compared with the output voltage of the potentiometer. The difference between the voltages determines the deflection of the fuel gauge pointer." This is from the manual. You should check with a multimeter that you have the 5V at the sender and a varying voltage from it's output when you move the float arm. It may be that the sender is faulty, do this test first and we can take it from there.
Nick


Have you checked the voltage delivered to the sender unit as above and checked for any output?

[sierrafery]

Actually the explanation from RAVE in this case is not the best as the sender's variable resistance is sensed by the gauge on the earth path as the sender's one side is to earth(pink/black wire) and the other is connected to the gauge which gets the supply from the instrument pack, a bit contradictory i know but the diagram confirms the description of the fuel gauge from the instruments section:

"The signal input for the fuel gauge is from the tank sender unit, it is a variable voltage signal proportional to the level
of fuel in the tank. The instrument pack provides the power via fuse 27 to the fuel gauge, then from the gauge on to
the fuel tank sender unit. The earth path return circuit of the sender unit is connected to the instrument pack.

IMO the answer lies in the following statement

1. disconnected the electrical plug at the sender/pump unit, put the multimeter across the sender pins = open circuit (with tank 3/4 full)

which means the pump must come out and see if the sender(potentiometer) is not interrupted at a joint or something cos at 3/4 tank you must get around 36 Ohm reading(see attachment)... there vare senders as spare on the market part number YAD500040

[Pippin]

At the risk of being pedantic 'earth path' is not the same as 'ground', the point of my previous post is that checking the supply voltage at the sender and for any output voltage is all that needed to be done to determine where the fault probably lies. I was concerned that all the other actions that Geoff took were unnecessary and could potentially cause other faults.
Nick

[sierrafery]

I didnt try to undermine your intervention just to clarify that there's a kinda contradiction between descriptions in RAVE and that in reality there's no ''supply'' to the sender, it's the return through the gauge cos the sender works as a variable resistance on the earth path(ground) but as long as there's open circuit on the sender's terminals any other measurement seems irrelevant