Faulty fuel gauge

[Beadybc]

Turned the car on earlier and it had decided that there was no more fuel, which is strange since I put £50 worth of fuel in last night. So I went to fill up the tank and it only took £15 worth until it was full.

Whilst driving along the motorway the gauge crept up until it showed about 30% full but went no further than that for a while. After I came off the the motorway and drove around a bit it started fluctuating anywhere between 5% and 60%, it didn’t fluctuate quickly and it never went over 60% full.

Is my car a special self-generating fuel model or should I start looking for a problem somewhere?

1997 945 B230FK

[SalvadorP]

Originally Posted by Beadybc

Is my car a special self-generating fuel model

Most likely.

Or, it can be faulty. You should probably remove the instrument cluster and inspect for a bad connection. A multimeter would help.
Or the tank sender is bad.

[Beadybc]

Originally Posted by SalvadorP

Most likely.

Or, it can be faulty. You should probably remove the instrument cluster and inspect for a bad connection. A multimeter would help.
Or the tank sender is bad.

What connection would I be using the multimeter on and what reading should I be getting?

[john.wigley]

Temperamental fuel gauges are a well known issue on 7 and 9 series cars, 'Beadybc'. I lived with one for years. Just brimmed the tank every time, zeroed the trip, drove c250 miles and repeat. Carried a 5L can for emergencies. I never had cause to use it myself, but was able to help out a number of other motorists!

Regards, John.

[SalvadorP]

Originally Posted by Beadybc

What connection would I be using the multimeter on and what reading should I be getting?

This guy had a similar issue and he goes through the process of diagnostic and fixing it in this video.

https://www.youtube.com/watch?v=TWq4TIeSSv0&t=550s

Also this thread from another forum might have useful info for you: https://volvoforums.com/forum/volvo-...-issues-82850/

[Forrest]

There is fairly comprehensive trouble-shooting guidance in the FAQ too.

https://www.volvoclub.org.uk/faq/Ele...augeFluctuates

There should be a multi-plug connector in the luggage compartment area which makes it reasonably simple to interrupt the circuit to the sender for testing purposes. There are four wires in this connector. The thinner ones are for the fuel gauge and the thicker ones for the in-tank pump.

Getting the instrument cluster out on a 940 is quite simple. Accessing the fuel sender a bit less so. This may influence the order in which you test components.

Good luck.

[gpl1968]

If your gauge is sticking in one position it could be a worn contact on the fuel tank sender.



In the above pic the left hand part is the good one. The part is attached to a float in the fuel level sender and it slides up and down two coiled resistor wires with the rectangular ends making contact, one to each resistor wire. The right hand part is worn with the rectangular contact patches worn and liable to catch on the resistor wires giving a bad reading on the fuel gauge.

I had this problem and managed to silver solder replacement rectangles onto the part using nickel silver. It works fine now although it still sticks sometimes.

There is an article on the subject in the FAQ: linky.

[Beadybc]

Ok so it is definitely the in tank unit that is the problem. I tapped the body above the unit with a rubber mallet and the car started reading 60% full instead of empty. It should have about 80-90% fuel so it's getting stuck at 60%.

Took the unit out to confirm and found that past a certain point of raising up, the float does get stiffer. Basically, closer to the top end it does not slide up smoothly anymore.

P.S: I did do the checks with a multimeter on the back of the fuel gauge and found that it was working.

[Forrest]

Following on from gpl1968’s post a related issue I have seen once in a spare tank sender unit I had available is the two coiled resistor wires coming adrift at the bottom of the telescopic tube in which they are housed. I am not sure how they are meant to be fixed there. There are two small holes in the bottom of the tube in which they are supposed to sit. It is easy enough to check whether the resistor coils are still in these holes and, if they have come adrift, you can at a pinch reposition them by manipulating the top ends without having to dismantle the assembly. What I never got around to testing is whether that is it or whether they should be clipped, glued, etc. in position.

[mjk164]

I had just this on my 1993 960 some years ago now, and Gavin (gpl1968) describes it very well. Getting the sender unit out of the tank is fiddley and needs patience but I also soldered new rectangular ends onto the existing carrier and it has worked well for several years. Be bold and get at it!
Good luck.