Fuel gauge issues

[Chambo110]

Afternoon fellas.

Not used my truck for a good a few weeks. Today I went out on a 2 hour trip with a full tank (allegedly) Only to find an hour in I was sat on side of m11 with no fuel but a full gauge!! 🤬🤬

now I’m home I see even with ignition off my gauge reads just under half?? Ignition on again and I’m full up.

am I looking at a new gauge, sender or something else ?

if the gauge has gone, do I need to replace gauge and sender or can new gauges work with original sender ?

any help would be appreciated 

[monkie]

Could be a gauge issue, sender issue or wiring issue. Weird electrical issues often turn out to be earth faults. Always worth double checking the earth to the gauge and gauge body first. Maybe the sender float is snagged on a baffle in the tank. You can try some knocks on the tank from Land Rover special tool #1 (hammer) to see if that has any effect.

If the above doesn't help; pull the sender and gauge from the vehicle. Wire the sender to the gauage, provide a 12V supply to the guage. Earth the sender, gauge and gauge body. Move the sender float to empty, half and full observing the needle on the gauge.

My top tip: As removing the sender is an awkward job - get a spare sender (PRC8463 for diesel 110). you can then perform the test leaving your sender in situ. If the issue is elsewhere then you don't have to do anything with the sender. If it is the sender, then you have the spare good to go.

Having had this issue myself; I always reset my trip milage when I fill the tank so I know when I am expecting to run low despite any lies from the gauge.

 

EDIT: Obvious point to make, but... Now you know the tank is full, drive round a bit for 150 miles before attempting to remove the sender so you don't make an expensive mess!

Edited June 9, 2021 by monkie

[Chambo110]

Great info there thanks

should I have 12v at the sender ? Apologies wiring and me don’t mix 

[monkie]

IIRC the 12v supply goes to the guage then out the other side down the wire (green with black trace) to the sender, then out the sender to earth. The other wire on the sender (white with slate trace) is for the low fuel warning light. If you disconnect the wires from the sender, take a note/picture first so you don't muddle them up.

[pete3000]

Depending on the model you've most likely lost the earth to the sender, causing the gauge to over read. although you shouldn't see anything at all when ignition is off as the green (and black) wires which power the gauge are on the ignition feed. The green/black trace then goes to the sender which is then shorted to earth when empty and rises in resistance when full to around 300 ohms.

Edited June 9, 2021 by pete3000

[Chambo110]

Cheers fellas 

I was missing an earth on the gauge ?? Got 2 wires to terminals, 1 is live with ignition other is dead. Can’t remember colours sorry. (Maybe both green). I now have an earth but gauge is reading just about quarter tank with ignition off.

am I correct in suspecting the gauge??

Thanks

[monkie]

Once you know a few simple rules electrics on land rovers aren't that complex.

Black is always an earth and can be a big source of problems if not earthing reliably.

A solid colour is usually a live supply to switch (supply can be permanent live unfused (brown), permanent live fused (purple), ignition on unfused (white) or ignition on fused (green)).

Wires from a switch or gauge to accessory carry a stripe to tell you where they go. The gauges are powered by a fused ignition on live (green). They are earthed (black) and they have a wire to a sender (coloured trace).

Something weird going on here. You should have a green wire to the gauge, a black wire the back of the gauge body, a green with black trace. Looking at the sender you should have the green with black trace wire from the gauge, white with grey trace which is for the low fuel warning dash lamp and a black earth wire. 

 

Check those earths first. Buy a new sender (they aren't expensive) and then wire the gauge to it out the vehicle and you can check the gauge function as you move the sender float arm. 

[western]

On pre td5 gauges the gauges earth wire is daisy chained from the earth connection to each gauge threaded rod on back of each gauge, the earth wire ring terminal should sit on top of the metal U clamp & be secured with a washer & a knurled edged thumb nut. also make sure the metal U clamp is not touching the other terminals.

[Chambo110]

Monkie.. wow, cheers for taking the time to explain, very useful. 
I will struggle to get any checks done today. I’m sure the gauge is as you say .. green, a green/trace of some sort. Now it has the additional black to the earth post as Ralph mentioned below.

 

Ralph, I should of added at start that it’s a 1987 110csw originally 2.5 but now 200tdi

my sender at tank is caked in crud. Couple of joins, generally a mess. Which I intend to sort. 
but it’s as the version below 

 

thanks again gentlemen 

 

[western]

that looks like a 300tdi sender. 

not like my earlier version.

[Chambo110]

The above pic isn’t my one.. pretty sure it’s the same. Just going from memory though.

I’ll get time tomorrow to get underneath and have a proper look 

thanks Ralph