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volvo 740 fuel guage

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Old Jan 30th, 2019, 20:59   #1
atco
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Default volvo 740 fuel guage

just wondering if anyone can tel me why the fuel guage on my 89 volvo 740 is not working and if there is a video on this item for diagnostic repair.thanks
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Old Jan 31st, 2019, 00:08   #2
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For an introduction to the topic try the FAQ on this site; start with the homepage and go to Volvo owners club - car info - 700/900 FAQ - Troubleshooting - Electrical instruments - Fuel gauge fluctuates or fails to work.
After this use the Search button - Advanced search - keyword (volvo 940 fuel gauge) - search in forums (700/900 series general) and the appropriate threads will display, I've not seen any videos but some threads have photos of the sender, wiring etc.
It would appear that there are 3 possibilities, the gauge itself, the instrument panel pcb and the most likely, namely the sender itself.
I have not looked on you tube, but google will also offer some assistance.

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Old Jan 31st, 2019, 00:10   #3
Laird Scooby
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The gauge has probably died.



That was my solution until i found a fully working set of instruments on fleabay. Note that Yazaki and VDO instruments are NOT interchangeable. There is an obvious difference on the odometer, i think it's that on the Yazaki there are bars separating the digits, on the VDO (mine in the picture) there isn't BUT i might have that the wrong way round - it tells you somewhere in the FAQ which is which.

It's about 6 years since i did that so my memory is a little hazy on it now.
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Old Jan 31st, 2019, 16:17   #4
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Got got it right Dave
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Old Jan 31st, 2019, 16:34   #5
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Your instrument cluster being in an '89 740 is almost a certainty a VDO. After this time the most likely cause of a flickering/bonkers/iratic fuel gauge is the small pcb built into the back of the gauge itself has developed a fault. This can be either a bad solder joint or a duff electrical component. If you can find a working one anywhere (unlikely) the easiest cure is to replace it.

Other causes can be a faulty in-tank fuel sender, a poor input connections/earth usually at the back of the cluster on the blue plastic distribution circuit/s. It is unusual for the blue blue plastic circuitry to fail. If it has it is likely it will be obvious to the eye.

If the car has not been used much you can get problems with the resistance slider inside the in-tank sender.

If you can locate the right Volvo Green Book (TPxxxx) online you can test the input/output resistance values for the fuel gauge at the cluster. I have one somewhere and if I locate it I will put up it's TP number. Bob.
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Old Jan 31st, 2019, 17:42   #6
Laird Scooby
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Thanks Bob - thought i was right on the Yazaki/VDO differences. Nice to have it confirmed though!

Onto the sender unit, there are three wires accessible on a 3-pole multiplug under the left hand boot cubby-hole cover. There are red and brown, +12v for the pump and earth respectively. There is also a pink wire, i can't remember if it's pink on the sender side of the plug or the car side - doesn't matter as long as you can find the pink one and then unplug the 3-pole multiplug.

Connect a 22 ohme resistor between the "pink" one and brown, switch the ignition on and the gauge should crawl up to zero ish.

Now remove the 22 ohm wire it in series with a 270 ohm resistor and fit that accross the pink and brown, the gauge should move fairly quickly to full ish.

These are approximate values to test the gauge (and obviously the wiring in between), if memory serves the exact values are 20 ohms and 290 ohms but they are close enough for all practical testing purposes.

Most likely cause is the gauge though, they have a nasty habit of failing and/or developing the work ethics of a 1970s coal miner - in other words they're on strike 90% of the time but work ok when they're not! My 760 fuel gauge is like that but isn't even that accurate when it does work! I suspect its sender came from a 760 saloon with the extra sender unit in the auxiliary tank behind the seats.
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Old Jan 31st, 2019, 19:40   #7
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Quote:
Originally Posted by bob12 View Post
Your instrument cluster being in an '89 740 is almost a certainty a VDO. After this time the most likely cause of a flickering/bonkers/iratic fuel gauge is the small pcb built into the back of the gauge itself has developed a fault. This can be either a bad solder joint or a duff electrical component. If you can find a working one anywhere (unlikely) the easiest cure is to replace it.

Other causes can be a faulty in-tank fuel sender, a poor input connections/earth usually at the back of the cluster on the blue plastic distribution circuit/s. It is unusual for the blue blue plastic circuitry to fail. If it has it is likely it will be obvious to the eye.

If the car has not been used much you can get problems with the resistance slider inside the in-tank sender.

If you can locate the right Volvo Green Book (TPxxxx) online you can test the input/output resistance values for the fuel gauge at the cluster. I have one somewhere and if I locate it I will put up it's TP number. Bob.
The fuel gauge on my 740 is erratic, but I just live with in and do what I always do (and my dad did) was reset the trip counter to zero when I fill it up and I know roughly how many miles I've done when I need to fill up again.
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Old Jan 31st, 2019, 21:13   #8
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The fuel gauge on my 740 is erratic, but I just live with in and do what I always do (and my dad did) was reset the trip counter to zero when I fill it up and I know roughly how many miles I've done when I need to fill up again.
You are fortunate that your mileometer and trip meter are still working Kevin. Long may it remain so, but to help don't forget not to reset the trip meter on the move. Bob.
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Old Feb 4th, 2019, 17:28   #9
atco
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Default fuel guage 740

ive seen a 960 for breaking .is it possible to take the guage out of that one and transfer over to the 740
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Old Feb 4th, 2019, 19:46   #10
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Originally Posted by atco View Post
ive seen a 960 for breaking .is it possible to take the guage out of that one and transfer over to the 740
Expels air from lungs through nose as answer unknown.

I have never tried to do it although I have a VDO that I put a Yazaki voltmeter in ... but that was a slightly different exercise.

The fuel gauge diameter/hole on the backboard are both very likely to be the same size, and I suspect there is nothing different in the in-tank senders between the two gauges. What is different maybe the method of fixing the gauge to the backboard and definitely the connection of the electrical inputs from the gauge to the backboard.

That said, and with thought it may be possible to work out how to connect up a Yazaki fuel gauge to a VDO.

As said, I have not had to think about or try this ... yet!

Bob.
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