Fuel gauge not moving

#1
Probably been asked before but can't find exact symptom.
Based on Hanes manual, only thing I can do is to check the fuel sender wires which I did and both are attached.

Tried to clean the fuse 3/4 both the top and the bottom cables but still nothing. What else can I do? It was working
well till today when my tried to fix the panel/gear selector light. No the latter works but I lose fuel reading.
Sender is working as Al fixed it himself and I do have more than a half tank before the needle stopped working altogether.
 
#2
Try earthing the sender cable. start at the sender and work back to the guage. sounds like you have knocked a wire off somewhere. You could start at the guage, if it doesn't go to full (slowly) then either the guage or the voltage regulator that plugs in across it is faulty. If it goes to full then its in the wiring post guage. Wiring pre guage is also an option; to test earth a 12v bulb and connect other end to the input terminal wire. It should light up with IGN on.
 

colnerov

Well-Known Member
#3
Hi, Is the temp gauge working as it should? If yes then it's the fuel gauge, wire or sender.
If no , then it's the voltage regulator or its supply from the fuse, and as you have been
fiddling in the fuse box area then as said a fuse may have been dislodged. The fuse boxes
can be a bit tempermental.

Colin
 
#4
mikecoombs said:
Try earthing the sender cable. start at the sender and work back to the guage. sounds like you have knocked a wire off somewhere. You could start at the guage, if it doesn't go to full (slowly) then either the guage or the voltage regulator that plugs in across it is faulty. If it goes to full then its in the wiring post guage. Wiring pre guage is also an option; to test earth a 12v bulb and connect other end to the input terminal wire. It should light up with IGN on.
Hi MIke, thank you for looking into this. I took out one wire at the time from the sender and nothing happened. Previously it used to work as in the needle goes all the way to full. Is the voltage regulator the small box by the driver side that has 4 pins and screwed to the wing near the firewall? The temp gauge is working however, so I doubt it's the regulator, I can't be certain. Does this seem to you post or pre wiring?
 
#5
If you earth the sender wire at the tank end the gauge should go to full (don't earth it to a fuel pipe). If youjust disconnect it it should stay on empty. The voltage regulator is a small tin box about 1/2" by 3/8" by 1 1/2" ish and it plugs into the back of the gauge itself on two lucar connectors. Its job is largely to slow the gauge movement down so it doesn't flick all over the place with waves in the tank. the box at the side of the glovebox is the Alternator's regulator.

what you are trying to do is locate the point at which the electricity stops coming. Given the temp guage works ok and it shares the regulator with the fuel guage then the circuit is good up to the regulator output which rules out both regulator and fuse as the cause. so it is between regulator and sender earth. The two wires at the sender are the line to the guage and an earth line to the chassis. so check the connection between the regulator and the fuel gauge, check to see if the fuel guage actually works with 10volts across it and check the outgoing wire that heads off to the sender. From what youhave said youshould have found it by then as the last piece is to check if the wire from the gauge to the sender is intact (long lead and an ohm meter or battery and light).

obviously if shorting the sender unit wire to earth porduces a full tank at the gauge the issue is the guage sender or it's earth and you can forget about doing all the above.

If it is the sender, drive the car around till you need to use the reserve then take it back to Al to fix....It isn't hard but it is awkward and you can cover yourself with petrol easily. It's best done on a hoist with a bucket under it.
 

ghce

Well-Known Member
#7
I have seen the genuine Lucas smoke for sale but have never seen the smoke reinjection tool that you would need to install it.
It's on the net so it must be true!


Graeme
 
#8
mikecoombs said:
If you earth the sender wire at the tank end the gauge should go to full (don't earth it to a fuel pipe). If youjust disconnect it it should stay on empty. The voltage regulator is a small tin box about 1/2" by 3/8" by 1 1/2" ish and it plugs into the back of the gauge itself on two lucar connectors. Its job is largely to slow the gauge movement down so it doesn't flick all over the place with waves in the tank. the box at the side of the glovebox is the Alternator's regulator.

what you are trying to do is locate the point at which the electricity stops coming. Given the temp guage works ok and it shares the regulator with the fuel guage then the circuit is good up to the regulator output which rules out both regulator and fuse as the cause. so it is between regulator and sender earth. The two wires at the sender are the line to the guage and an earth line to the chassis. so check the connection between the regulator and the fuel gauge, check to see if the fuel guage actually works with 10volts across it and check the outgoing wire that heads off to the sender. From what youhave said youshould have found it by then as the last piece is to check if the wire from the gauge to the sender is intact (long lead and an ohm meter or battery and light).

obviously if shorting the sender unit wire to earth porduces a full tank at the gauge the issue is the guage sender or it's earth and you can forget about doing all the above.

If it is the sender, drive the car around till you need to use the reserve then take it back to Al to fix....It isn't hard but it is awkward and you can cover yourself with petrol easily. It's best done on a hoist with a bucket under it.
I can't thank you enough Mike, you really took the time to explain it in a layman way. Just that electricals are my archilles heel...just need time to absorb it. I really want to fix this myself and not bother Al too often. :) He is like my personal tech support these days and I feel bad about it. I will get on it and update you real soon. Thx again.
 
#9
Mike finally figured out your tips above. What's the best way to get to the connection between the regulator and the fuel gauge? Taking out the dash panel is tough.
 
#10
I just combined the 2 wires at the tank and the needle went all the way up. Guess it's time to buy replacement sender. Anyone know how to get one, let me know please. Mark Gray doesn't look like they have it. WIll check at Rimmer Bros now.
 

vaultsman

Well-Known Member
#11
Hi,

You probably know, so my apologies, but this is a typical (non-P6) fuel sender unit:



As the fuel level in the tank rises and falls, the float arm swings which varies the electrical resistance (in Ohms) of the unit.

Complete senders don't come up for sale very often but, most commonly, sender faults are down to a punctured float. So before you try sourcing a complete unit, it's worth removing the unit from the tank and checking whether this is the case. Before you remove it, put marks on the sender and tank to make sure it goes back in the same orientation.

The floats are not specific to the P6 and can be picked up far more readily than complete senders.

If you have a multimeter, you can also check the unit itself by attaching the meter probes to the two terminals, and slowly moving the arm with the meter set to read Ohms. The resistance should vary smoothly through the range of arm movement. Even if faulty, they can be repaired with care.

Good luck!

Stan
 

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#12
It's probably not a float issue. I removed the sender and it was rusted in place so I dismantled and cleaned it as best I could, lubricated it and tested and it seemed to work. Unfortunately it only lasted a couple of weeks before failing but given it's condition I'm not entirely surprised. I seem to be out of spares at the moment. Any ideas of a fix?
 

vaultsman

Well-Known Member
#13
rafrover said:
I just combined the 2 wires at the tank and the needle went all the way up.
Given Al's comment above, and that the gauge goes full-scale when you've disconnected the 2 female spades from the terminals and connected them together, it does look as if it could well be the sender itself.

However, you could disconnect the two spades, put your multimeter on the two sender terminals, and see what (if any) resistance reading you get.

I've just checked my spare sender and in the empty position the resistance is 250 ohms. In the full position it's 16 ohms.

If you get anywhere between these figures (and you can estimate what the reading should be if you've an idea how full the tank is), the sender would seem to be OK and the fault is probably elsewhere. If you get no resistance reading at all, then it's open circuit and the sender is faulty.

Also, if you know there's a decent level of fuel in the tank and you get a reading around 250 ohms, I'd suggest the float is the problem.

Stan
 
#14
Thats great. I'll have a go later today. One thing for sure is the fault came about when the tank was half full. Now I just switched to the reserve tank, so probably left about 4-5ltrs in it.
 
#15
vaultsman said:
rafrover said:
I just combined the 2 wires at the tank and the needle went all the way up.
Given Al's comment above, and that the gauge goes full-scale when you've disconnected the 2 female spades from the terminals and connected them together, it does look as if it could well be the sender itself.

However, you could disconnect the two spades, put your multimeter on the two sender terminals, and see what (if any) resistance reading you get.

I've just checked my spare sender and in the empty position the resistance is 250 ohms. In the full position it's 16 ohms.

If you get anywhere between these figures (and you can estimate what the reading should be if you've an idea how full the tank is), the sender would seem to be OK and the fault is probably elsewhere. If you get no resistance reading at all, then it's open circuit and the sender is faulty.

Also, if you know there's a decent level of fuel in the tank and you get a reading around 250 ohms, I'd suggest the float is the problem.

Stan
Hi Stan, firstly thanks again for the above. I just did the 'test' using a multimeter and strange things happened.

Firstly, there is no reading coming from the sender spade plugs when I set it to 200 on the Ohm section of my multimeter. I had to move it 200K to get some reading.
Just to be sure, the red plug/lead is attached to the spade without the enclosure and the black to the one that has the enclosure. The reading shows 42.2 and it took a 10 minutes to climb to that number and I think it has stopped climbing and that's the number I got. My hands feel numb from holding those leads but I managed to stick the sharp needle ends into the hole in the spade plugs.

So I don't know if I am doing it all wrong. What can you read into all this?
 

vaultsman

Well-Known Member
#16
Hi,

Not sure why the meter should take that long to register, but at that reading negligible current will flow through the gauge so it won't move at all.

The problem sounds like it's either the sender resistance unit or possibly an issue with the riveted terminals on the sender.

Either way, it'll have to come out - which I'd do before trying to source a replacement.

The brass fuel line nuts are 3/8" Whitworth. If you haven't got an open-end spanner for these, you might get away with 19mm but be wary of rounding the nuts off. Mark the sender orientation to the tank, then use a punch to knock the retaining ring round anti-clockwise. You'll have to wiggle the sender around to get it out through the opening.

Stan
 

colnerov

Well-Known Member
#17
Hi, I think the meter is acting the way it does is because the meter uses a voltage to measure
resistance, which is warming the senders resister wire and changing its resistance. As you saw
it does eventually settle down. Don't worry it won't blow up because petrol doesn't burn, petrol
vapour burns, but it can't do that because it's far too rich an atmosphere in there.

Colin
 

vaultsman

Well-Known Member
#19
rafrover said:
Failing which, I saw a universal sender on a local site. Do you guys think it can work? https://trademe.co.nz/981421330
I wouldn't have thought so, I'm afraid.

The flange is a different fixing to yours, and likely as not will be the wrong diameter/wrong resistance range anyway.

Stan

EDIT: I'd still pull your existing sender to check it over before buying a replacement. It may well be repairable.

Good luck!
 
#20
vaultsman said:
rafrover said:
Failing which, I saw a universal sender on a local site. Do you guys think it can work? https://trademe.co.nz/981421330
I wouldn't have thought so, I'm afraid.

The flange is a different fixing to yours, and likely as not will be the wrong diameter/wrong resistance range anyway.

Stan

EDIT: I'd still pull your existing sender to check it over before buying a replacement. It may well be repairable.

Good luck!
Thanks Stan, sound advice. Will touch base with Mike and see what parts he has. Thanks again.
 
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