Fuel Gauge not working...heeeelllllp!

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Flyingchunk
Posts: 59
Joined: 04 Sep 2012, 20:44
80-90 Mem No: 11572
Location: Crawley - West Sussex

Fuel Gauge not working...heeeelllllp!

Post by Flyingchunk »

Ok.

Recently sent van into mechanics to sort numerous issues I have no time to.

Fuel gauge not working was one of them.

They dropped the task and replaced the sender (logical fix I agree).

Got it back, and the needle only moves a tiny bit passed red the drops back down with what I know is at least half a tank I it.

So... What can it be?

Any ideas? What can we / they do (it's going back tomorrow for more investigation)?

We're supposed to be going to France for two weeks next Tuesday for my 40th.

It would be heartbreaking to have to take the tent (for the second year running!!)

Please 80-90 buddies....save our holiday.

Wife is not happy with going long range without knowing how much is in the tank.

Even a temporary solution will do.

Cheers in advance
1981 - Devon Moonraker - 2.0l Aircooled

MidLifeCrisis
Posts: 555
Joined: 20 Nov 2011, 19:07
80-90 Mem No: 10519
Location: Bagshot, Surrey

Re: Fuel Gauge not working...heeeelllllp!

Post by MidLifeCrisis »

It sounds like the wire from the fuel gauge to the fuel sender is seeing 'too much resistance' (not very technical I know!)

Basically the gauge measures the resistance in the wire (and the fuel sender) - a large resistance and the needle shows empty, a small resistance and the needle shows full. The fuel sender has a variable resistance depending on how much fuel is in the tank - so that varies and in turn the needle on the gauge moves.

However if there is a large resistance in the wire from the fuel gauge to the sender (or from the sender to ground) then that would artificially 'drag' the resistance of the system up (and therefore the needle down).

In addition to all this, there is a voltage regulator in the dash that supplies the fuel gauge with a nice steady 10 volt signal - if this is malfunctioning then the gauge will also misread;

1) So, you need to check that fuel gauge positive voltage is correct at 10 volts.

2) Then you need to check the wiring from the fuel gauge to fuel sender, and then the wire from the fuel sender to ground. (or run a new good wire, and create a new good ground)

(fyi - according to Bentleys the resistance (to ground) at the fuel gauge terminal that connects to the fuel sender should be 288 ohms when the tank is empty, and 37 ohms when the tank is full)
(but finally - I'd just go on hols - fill up the tank, watch the mileage like a hawk and fill up often!!) :D :D
1987 Westfalia Van, Petrol 2.0 AGG

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The Bishop
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Joined: 14 Jul 2011, 11:44
80-90 Mem No: 10021
Location: Near Ipswich

Re: Fuel Gauge not working...heeeelllllp!

Post by The Bishop »

Mid LIfe Crisis seems to be very knowledgable on this.
And Again I would go on holiday and fill up often. Take a spare can with you and what can go wrong?

I had a similar problem until last weekend and again, prompted by a trip to Spain, I have just dropped the tank out. I cleaned up the spade terminals, they were quite green, and cleaned up the contacts within the sender where the float registers its level. (while out I undersealed the tank and above the tank). All back together and working fine for me. Although interestingly full is not quite full and so taking the above post I must have some resistance in the wire.

Prompted by the green terminals and the fact that we had a starter motor problem as a result of green terminals. I have started going around cleaning up terminals and giving them a little squirt of WD40/GT40 to avoid unexpected electrical faults.
1986 1.9 Petrol/LPG with Devon pop up.

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Flyingchunk
Posts: 59
Joined: 04 Sep 2012, 20:44
80-90 Mem No: 11572
Location: Crawley - West Sussex

Re: Fuel Gauge not working...heeeelllllp!

Post by Flyingchunk »

Well...here's an update.

All working.

Sure enough green / croded terminals to the gauge on the dash board.

Oh well...peace of mind tank is ok and there's a new sender in there can't be a bad thing.

Top stuff guys. Thanks
1981 - Devon Moonraker - 2.0l Aircooled

weimarbus
Posts: 608
Joined: 19 Jun 2010, 12:53
80-90 Mem No: 10165
Location: coulsdon

Re: Fuel Gauge not working...heeeelllllp!

Post by weimarbus »

Good news, start packing :ok
1985 hi-top 2.1MV with DG carb and LPG
1955 trials buggy with 1.9 DG high lift cam and twin dell's (now sold)
1972 1303 beetle
1992 Audi 100 2.8 quattro estate

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