Fuel gauge reading zero ish after long period off road

User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Fuel gauge reading zero ish after long period off road

Post by Nocky »

Hi all, I realise there have been many many posts about this topic, and I swear I’ve read them all, but none really fits my problem.
Before my bus went in for body work, the fuel gauge worked (To a fashion) the old 3/4 full when fully full, but no drama there, I can live with that, however, since getting it back, my fuel gauges fails to register a full (3/4 tank)

I have checked the connections at the rear of the gauge and all seems to be ok, and I can confirm when the ignition is turned on, the gauge needle does move ever so slightly, not a lot, but a little. I tried headlights on and that has no impact.

So, could the sender float be stuck ? Any simpLe checks I can do to determine root cause

Thanks in advance
1964 Microbus US import - The dream has become reality :bs:
User avatar
vwJim
SSVC Committee Member
SSVC Committee Member
Posts: 20129
Joined: Thu Apr 24, 2003 6:05 pm
Location: under a bus in Hampshire...
Contact:

Re: Fuel gauge reading zero ish after long period off road

Post by vwJim »

You've not said what bodywork was done? They could of burnt the loom out when welding. Or not put items back in.

Take the cable off the sender and put it direct to earth. The gauge should read full. If it does, you know the gauge and cable is fine.

Tank should have an earth.
Supplying quality in house designed items plus parts from SyncLink, Kennedy Clutches, & CB Performance. Also fitting service including modifications & mechanical upgrades.
User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Re: Fuel gauge reading zero ish after long period off road

Post by Nocky »

vwJim wrote: Wed Jul 01, 2020 6:57 pm You've not said what bodywork was done? They could of burnt the loom out when welding. Or not put items back in.

Take the cable off the sender and put it direct to earth. The gauge should read full. If it does, you know the gauge and cable is fine.

Tank should have an earth.
Ah sorry, I had new front valance, new front arch ns, new rear arch ns, new sill inner & outer ns, new jacking point ns, new outrigger ns, and 1 new outrigger os, also had safari latches welded in. Any of that near the loom ?

I’ll try the sender cable Earth check tomorrow.

Thanks Jim
1964 Microbus US import - The dream has become reality :bs:
User avatar
vwJim
SSVC Committee Member
SSVC Committee Member
Posts: 20129
Joined: Thu Apr 24, 2003 6:05 pm
Location: under a bus in Hampshire...
Contact:

Re: Fuel gauge reading zero ish after long period off road

Post by vwJim »

Depending on how rotten the front was, the loom passes through that area.
Supplying quality in house designed items plus parts from SyncLink, Kennedy Clutches, & CB Performance. Also fitting service including modifications & mechanical upgrades.
User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Re: Fuel gauge reading zero ish after long period off road

Post by Nocky »

vwJim wrote: Wed Jul 01, 2020 9:03 pm Depending on how rotten the front was, the loom passes through that area.
Hi Jim, so, I took the fuel sender out of the tank to check the float was free, it looks new and the float moves up and down in the cylinder freely. I then earthed the lead that goes to the top of the sender and the gauge goes to full. I then checked voltage to coming through the cable (Not an expert with the multimeter) but it registers 7.5

I do notice movement on the needle when the ignition turns on, but it’s very minimal (Like it moves half way in between no power and the R) but I know I have a full tank of fuel.

So does that equate to a bad earth in the cab on the gauge ?
Last edited by Nocky on Thu Jul 02, 2020 2:38 pm, edited 1 time in total.
1964 Microbus US import - The dream has become reality :bs:
DUBious
Registered user
Posts: 5
Joined: Sat Dec 04, 2010 7:41 am

Re: Fuel gauge reading zero ish after long period off road

Post by DUBious »

Pics for clarity. I can get the gauge to work by doing a temporary earth from the one terminal to body (but am I just doing the same as I did my earthing cable to sender ?) Or is this correct and telling me the old earth to the gauge is dodgy ? ImageImageImage

Sent from my SM-G965F using Tapatalk

User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Re: Fuel gauge reading zero ish after long period off road

Post by Nocky »

Voltage readings from gauge with ignition on (Looking at pic 2 above - view from back of gauge)
Left most connection with green / black wire 4.73 volts
Middle connection black wire 0 volts
Right most connection green wire 11.93 volts

To ensure a good earth at the tank, I connected a new earth wire from sender screw to body screw and tested continuity.

And still the freaking gauge ain’t working. Next I got some brand new wire and used a length through the van from the sender to the gauge (Just to verify that existing wire) no changes.
So my thinking is, either the nearly new fuel sender is duff, or, as mentioned above, the gauge earth is duff. HELP #scratchhead
1964 Microbus US import - The dream has become reality :bs:
User avatar
Stevep
SSVC Member
SSVC Member
Posts: 349
Joined: Tue Apr 22, 2014 3:04 pm

Re: Fuel gauge reading zero ish after long period off road

Post by Stevep »

Image
The fuel gauge circuit is quite simple!
Most electrical problems are bad earth connections.


Sent from my iPhone using Tapatalk
User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Re: Fuel gauge reading zero ish after long period off road

Post by Nocky »

Stevep wrote: Thu Jul 02, 2020 5:16 pm Image
The fuel gauge circuit is quite simple!
Most electrical problems are bad earth connections.


Sent from my iPhone using Tapatalk
Thanks Steve, but I’ve already added 2 new earths (One from sender bolt to body & one from rear of gauge to body) so pretty sure they are fine as I tested continuity on both)
1964 Microbus US import - The dream has become reality :bs:
User avatar
Who.Me?
SSVC Member
SSVC Member
Posts: 1062
Joined: Thu May 15, 2014 8:13 pm
Location: West Sussex

Re: Fuel gauge reading zero ish after long period off road

Post by Who.Me? »

I'd agree that a bad ground is most likely the problem. My gauge is in a bracket mounted below the dash and doesn't have a great ground. Occasionally the gauge will either read nothing or the needle will jump like a dying fish. That tells me when I need to clean the ground.

But if the ground isn't the problem... the inside of the tubular sender has a float that rides up and down two very fine wires. The wires are known to break, apparently randomly, so the sender can fail but the float will still go up and down. Some guys on the Samba have repaired them, but if that's the problem I'd buy a new sender rather than try to repair it. Not sure whether a broken wire would cause the gauge to peg off the scale, or fail to register anything though?

Have a look at the pictures at the bottom of this thread to see what I mean about how the sender works... https://www.thesamba.com/vw/forum/viewt ... 59#9359159
User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Re: Fuel gauge reading zero ish after long period off road

Post by Nocky »

Who.Me? wrote: Thu Jul 02, 2020 6:46 pm I'd agree that a bad ground is most likely the problem. My gauge is in a bracket mounted below the dash and doesn't have a great ground. Occasionally the gauge will either read nothing or the needle will jump like a dying fish. That tells me when I need to clean the ground.

But if the ground isn't the problem... the inside of the tubular sender has a float that rides up and down two very fine wires. The wires are known to break, apparently randomly, so the sender can fail but the float will still go up and down. Some guys on the Samba have repaired them, but if that's the problem I'd buy a new sender rather than try to repair it. Not sure whether a broken wire would cause the gauge to peg off the scale, or fail to register anything though?

Have a look at the pictures at the bottom of this thread to see what I mean about how the sender works... https://www.thesamba.com/vw/forum/viewt ... 59#9359159
Cheers Who Me, I am getting to the point of just ordering a new sender. I’m going to one last check of the ohm’s at sender tomorrow, I’ll test ohm’s when in tank and as it’s full, it should read low ohm, then I’ll draw it out of tank so float drops and see if it goes up. I don’t think it’s a bad earth as I’ve added 2 new earths, but I’ll rough them up for good contact and add a knurled biting washer to ensure it’s good. (thanks for the samba link, i might try and fix it if it’s duff, looks pretty simple to fix)
1964 Microbus US import - The dream has become reality :bs:
User avatar
vwJim
SSVC Committee Member
SSVC Committee Member
Posts: 20129
Joined: Thu Apr 24, 2003 6:05 pm
Location: under a bus in Hampshire...
Contact:

Re: Fuel gauge reading zero ish after long period off road

Post by vwJim »

Maybe it's being caused by the flat battery (or serious volt drop) 11.93v is rubbish.

Did you remove the sender wire off the tank and put it direct to earth? What happened with the gauge?

IMHO the gauge always needs a dedicated earth cable.

The tank should also always have an earth cable from a bolt head.
Supplying quality in house designed items plus parts from SyncLink, Kennedy Clutches, & CB Performance. Also fitting service including modifications & mechanical upgrades.
User avatar
Nocky
SSVC Member
SSVC Member
Posts: 106
Joined: Sat Oct 19, 2019 9:06 pm
Location: Quarry Bonk, West Mids

Re: Fuel gauge reading zero ish after long period off road

Post by Nocky »

vwJim wrote: Fri Jul 03, 2020 6:27 am Maybe it's being caused by the flat battery (or serious volt drop) 11.93v is rubbish.

Did you remove the sender wire off the tank and put it direct to earth? What happened with the gauge?

IMHO the gauge always needs a dedicated earth cable.

The tank should also always have an earth cable from a bolt head.
Hi Jim, as you suggested I tried the earthing of the sender cable, and the gauge to briefly go straight to full, I also added 2 new earths, one from gauge to body underdash screW, and another from sender bolt to main earth in engine bay. All to no avail.
I will double check them today when it stops ....... down, and I’ll also check ohm’s on sender. (guess I also need to charge battery and check that too, but that could be my use of the multimeter) I’ll do that first and recheck. And failing any of that helping fix it, I’ll strip the sender unit down and see if the wires are intact.
Thanks for the replies guys.
1964 Microbus US import - The dream has become reality :bs:
User avatar
Andy C
SSVC Member
SSVC Member
Posts: 47
Joined: Wed Sep 04, 2019 10:31 am
Location: Leamington Spa, Warwickshire

Re: Fuel gauge reading zero ish after long period off road

Post by Andy C »

I went through all of the above with my fuel gauge. The original gauge was stuck on 1/4 full so needed a new gauge. As the bus had been converted to 12v I thought - 'Great, buy a new 12v gauge (Same as the one in the picture above) with the same resistance range for the sender and all will be good'.

I put the gauge in and with a full tank it read 1/2 full. I then tried the Wolfsburg West 12v gauge and that did the same. I then changed the sender with a new VDO one and still no different. In the end I bought a second hand original 6v gauge from ebay and hey presto it worked!

The 6v gauge on 12v means the needle snaps round very quickly when the ignition is switched on. To limit this I fitted a voltage regulator used on old British Leyland Smiths gauges which I had laying around in the garage. It regulates the voltage to 10v and reduces the aggressive needle movement; the gauge is still as accurate as it can be. At some point I'll wire in a 6V voltage dropper to reduce this further.

I really have no idea why the 12v gauge wouldn't work. Hope this helps!
1964 Australian built 'Kombi'
DUBious
Registered user
Posts: 5
Joined: Sat Dec 04, 2010 7:41 am

Re: Fuel gauge reading zero ish after long period off road

Post by DUBious »

So, no rain today so decided to tackle this again, I found a connection supplying 12.3v and tried that on gauge (no change) redid earths 1 on tank, 1 on gauge (both dedicated) no change, I then took the sender unit out and measured ohms when in, and as I retracted it. 51 ohms in, and 51 ohms when out ! Hummm
So
I decided to take the sender unit apart. Now please correct me if I am wrong, but surely the float should not be full of fuel ???? I mean how can it float if its full of fuel !
Its hard to see in the pics, but if you zoom in you can see the fuel in the float. I tested it out (not sure why I did that as I know it won't float when full) but I tested it out non the less in a bucket and of course it won't float duh
Whats confusing me is, how the hell the fuel got inside when I can't seem to get it out ??? Am I stupid ?ImageImageImage

Sent from my SM-G965F using Tapatalk

Post Reply