V90 Fuel Gauge

Forrest · May 9th, 2021, 20:48

Time to start a few minor jobs on my new to me 1997 V90 bought from someone on the forum. In actual fact it’s in pretty good condition and doesn’t need much. But first on the list is the non-functioning fuel gauge.

The instrument and the cable as far as the rear cubbyhole appear to be alright. The gauge is permanently showing empty with the low fuel indicator illuminated. The tank is currently full. If I undo the 4-pin connector in the cubbyhole and short the two wires associated with the gauge (the two finer gauge wires) the gauge goes rapidly to full upon turning the key to position 2. The resistance across the pair of wires to the in-tank sender is 114 Ohms.

Presumably the problem is the float in the tank. Is this repairable or is it a case of finding a working exchange unit?

I am not afraid to remove the fuel sender having practised the art on my 1994 940 last year. But it there’s a potential quick fix I’ll take that too.

mjk164 · May 10th, 2021, 07:17

Hi Forrest, I had this same problem on my 1993 960 some years ago and traced it down to the tank sender unit. A bit of a pain to get at it but with patience and using the guidance in the VOC pages, you can get there. I found out that, after sorting out the dashboard gauge unit, there was a faulty tank sending unit after doing the same tests that you have done by joining sender wires, to gat a full needle deflection. When I eventually got the unit out, the slider that goes up and down with the level (to vary the resistance and send it to the gauge) had a badly worn sliding copper contact and I changed it for a good one from another unit. The sender units have different spiral lengths for different cars but the sliding contact part is the same, and can easily be changed. When I did mine, it has now done at least 80k miles so the repair is good. Good luck.

Forrest · May 19th, 2021, 21:34

Based on the recent discussion in this thread

https://www.volvoforums.org.uk/showthread.php?t=316866

I tried thumping the bottom of the tank and the gauge is now working again! I’m not sure whether it will prove to be a long term fix. However, it has to be the easiest car repair ever.

What made this worth a try was that I had previously narrowed the fault down to being the sender and tested the actual gauge. Another clue was that the low fuel light was illuminated. Dash PCB errors tend to cause the gauge to read empty without the light.

The method I employed was to stop the car over the crown of my sloping driveway and reach underneath with a rubber mallet. I thumped the tank in about the centre of the rear/bottom part roughly where the sender makes contact with the bottom of the tank.

Laird Scooby · May 19th, 2021, 21:58

Glad the percussive maintenance worked for you!

Exasperant · May 19th, 2021, 22:06

Quote:

Originally Posted by Forrest

What made this worth a try was that I had previously narrowed the fault down to being the sender and tested the actual gauge. Another clue was that the low fuel light was illuminated. Dash PCB errors tend to cause the gauge to read empty without the light.

Yeah, I had both stuck float and cluster issues!

Quite a relief when Fonzying it actually works.

May 19th, 2021, 21:58	#4
Laird Scooby Premier Member Last Online: Today 12:22 Join Date: May 2012 Location: Lakenheath	Glad the percussive maintenance worked for you! __________________ Cheers Dave Next Door to Top-Gun with a Honda CR-V & S Type Jag Volvo gone but not forgotten........

May 10th, 2021, 07:17	#2
mjk164 VOC Member Last Online: Apr 12th, 2024 13:08 Join Date: Aug 2006 Location: Hounslow West London	Hi Forrest, I had this same problem on my 1993 960 some years ago and traced it down to the tank sender unit. A bit of a pain to get at it but with patience and using the guidance in the VOC pages, you can get there. I found out that, after sorting out the dashboard gauge unit, there was a faulty tank sending unit after doing the same tests that you have done by joining sender wires, to gat a full needle deflection. When I eventually got the unit out, the slider that goes up and down with the level (to vary the resistance and send it to the gauge) had a badly worn sliding copper contact and I changed it for a good one from another unit. The sender units have different spiral lengths for different cars but the sliding contact part is the same, and can easily be changed. When I did mine, it has now done at least 80k miles so the repair is good. Good luck.

May 19th, 2021, 21:34	#3
Forrest VOC Member Last Online: Today 20:09 Join Date: Feb 2008 Location: Gloucester	Based on the recent discussion in this thread https://www.volvoforums.org.uk/showthread.php?t=316866 I tried thumping the bottom of the tank and the gauge is now working again! I’m not sure whether it will prove to be a long term fix. However, it has to be the easiest car repair ever. What made this worth a try was that I had previously narrowed the fault down to being the sender and tested the actual gauge. Another clue was that the low fuel light was illuminated. Dash PCB errors tend to cause the gauge to read empty without the light. The method I employed was to stop the car over the crown of my sloping driveway and reach underneath with a rubber mallet. I thumped the tank in about the centre of the rear/bottom part roughly where the sender makes contact with the bottom of the tank.

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