Inaccurate fuel gauge

[coggs]

My fuel gauge (1991 900 vert) reads empty when there is still about 6 gallons of fuel in the tank. A Saab central member has some used but operable sender units available for a reasonable price but before I replace it has enybody else seen this issue? I'm assuming it's in the sender and not the gauge. My odometer also doesn't work so I find myself filling up when I still have close to half a tank left just to be safe. Can the resistance check trouble shoot a calibration error - or just whether or not the sendig is funtioning? Is there a proceedure un the Bentley manual that outlines a step to check. Can't seem to find my book but will look harder if there is additional info in "the bible."

[16saabs]

where does it read when tank full?? what MPG are you getting
usually the tank sender under the boot floor, and it has probably seperated, but don't buy another YET. Run your car till low level indicated, then remove the keep ring, and then take out the sender unit carefully as you might find the outer casing has come loose, and if it's in the bottom of the tank you won't have to go in so deep with your hand to find it, sometimes it may be the float wires are contacting the low level indicator.
PM me your em address and I will send you a photo of a unit I have without outer casing.

[peva]

My low level light comes on at 5 gallons and reads empty at 3 gallons. Both my cars are very similar. The sender can fall apart sometimes. Then the reading is very erratic.

[16saabs]

mine usually takes 50+ UK ltrs when on full orange all the time
If the casing is missing/fallen off, your gauge will rise and fall when you go round corners or over bumps etc with about 5-6 gallons out, as the 'float' will just go with what's in the tank, but if the outercasing is in place there is just a hole in the bottom that lets the fuel in and out, and so it hardly alters in normal situations, eg corners, bumps etc

[dmgb5]

What your describing doesn't sound to be that far off from what I believe to be the norm. On my T16 the gauge reaches R and the petrol light comes on with about 4 gal left in the tank. IIRC was the about the same on previous T16 as well.

[16saabs]

they do usually read 'empty' well before they are, so that you don't strain/burn the pump out as no fuel to lubricate /keep it cool, another good Saab idea

[Rodentmaster]

If the time and interest is there, the gauge can be made to be more "faithful" (accurate is too strong a word to use).
It requires the instrument cluster connectors and copper be cleaned and tightened up (esp the ground connector) but the other improvement will be in the sender.
I have repaired the sender recently and installed a new low level reed sensor. Retightened the float contacts and resecured the base of the sender a little firmer than when it came out.
My reserve lamp is now acting at around 10 litres, gauge is acting more consistantly esp when low in the tank - needle position at empty is now on the red faithfully when before, it would be all over the low or red area or lower off the scale.....never the same each time the tank was low.

[crwchf01]

Originally Posted by Rodentmaster

If the time and interest is there, the gauge can be made to be more "faithful" (accurate is too strong a word to use).
It requires the instrument cluster connectors and copper be cleaned and tightened up (esp the ground connector) but the other improvement will be in the sender.
I have repaired the sender recently and installed a new low level reed sensor. Retightened the float contacts and resecured the base of the sender a little firmer than when it came out.
My reserve lamp is now acting at around 10 litres, gauge is acting more consistantly esp when low in the tank - needle position at empty is now on the red faithfully when before, it would be all over the low or red area or lower off the scale.....never the same each time the tank was low.

Don't happen to have a photo essay of the repair, do you?

[dmac02215]

I have a similar issue with my '89 c900 Turbo Hatch...when full, the fuel gauge reads ~1/2, then reads as "empty" with 6-7 gallons remaining...sometimes if I tap on the gauge it will temporarily show a more accurate reading - this is the furthest I have diagnosed it - anyone know of a relatively "simple" fix?

[KurBads]

Originally Posted by 16saabs

mine usually takes 50+ UK ltrs when on full orange all the time
If the casing is missing/fallen off, your gauge will rise and fall when you go round corners or over bumps etc with about 5-6 gallons out, as the 'float' will just go with what's in the tank, but if the outercasing is in place there is just a hole in the bottom that lets the fuel in and out, and so it hardly alters in normal situations, eg corners, bumps etc

This is interesting - mine vert`s fuel gauge reads full and empty but at low fuel level and on long turns (large roundabouts) I see fuel level indicator come up/go down and on right corners the empty warning light will come on and then go off at exit. I thought it`s normal but you make me wonder if not to take out the sender to have a closer look ...

[peva]

Originally Posted by KurBads

This is interesting - mine vert`s fuel gauge reads full and empty but at low fuel level and on long turns (large roundabouts) I see fuel level indicator come up/go down and on right corners the empty warning light will come on and then go off at exit. I thought it`s normal but you make me wonder if not to take out the sender to have a closer look ...

Your fuel gauge is normal Kurbads. The fuel sender unit is on the RHS side of the tank. When you go round a long LH turn the fuel level will then rise on the RHS of the tank and the fuel will also rise on that side and give a high fuel reading. The reverse will happen on long right hand turns. The fuel entry into the sender is through a relatively small hole so movement of the sender float is damped. If it wasn't damped by this small hole the fuel gauge would bounce up and down with every bump in the road. It takes a reasonably long turn to have these effects. It's only if you get fairly rapid movements of the gauge and/or warning light the gauge may be failing.

[16saabs]

Originally Posted by KurBads

This is interesting - mine vert`s fuel gauge reads full and empty but at low fuel level and on long turns (large roundabouts) I see fuel level indicator come up/go down and on right corners the empty warning light will come on and then go off at exit. I thought it`s normal but you make me wonder if not to take out the sender to have a closer look ...

KURBADS I would say your outer casing is missing, yes you get a bit of movement/ variation and I can be driving on flat and then go round a corner, and the light comes on, and then settles again, or up a light incline etc but only when I am very low on fuel, but never noticed the gauge move as usuually got my eyes on the road ahead especially round a corner lol

[coggs]

Thanks for all the replies. I've only had the car a short time so have not had the time to figure out exactly what my MPG is, but I only seem to be able to drive about 190 miles before the gauge is down in the reserve area, and a fill up is about 8 gallons. When full the gauge indicates full, but boy does it drop fast! The car run like it's new so the indicator is obviously off. I will follow up with some of the much appreciated suggestions before I replace it and let you know what I find.

[peva]

The tank should hold 15 gallons (UK), 68 litres. Just filled my car up today. The gauge was pointing toward the / in 1/2. So exactly half on the gauge. Took 24.19 litres (5.328 UK gallons). Odo read 161 miles (UK). So that was 30.2 mpg. That's a result and I haven't been hanging around. When my red light comes on I know I can get another 100 miles without running out, just over 3 gallons.

[16saabs]

Originally Posted by coggs

Thanks for all the replies. I've only had the car a short time so have not had the time to figure out exactly what my MPG is, but I only seem to be able to drive about 190 miles before the gauge is down in the reserve area, and a fill up is about 8 gallons. When full the gauge indicates full, but boy does it drop fast! The car run like it's new so the indicator is obviously off. I will follow up with some of the much appreciated suggestions before I replace it and let you know what I find.

even with the 190 miles if you do the mpg on that ,that will be ok, all I was wondering was if you wer eusing a lot of fuel..eg have a leak? so your MPG would be low but 8galls give 's you nearly 25 so foa a US Gallon that's not far off, very good especially if it's an auto but ok for manual, so it seems like your sender has probs as I said.