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Fuel gauge erratic (common question I'm sure!)

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Old Aug 29th, 2006, 23:47   #11
alsner
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Default It's possible BUT

Not if the majority of driving is around town, last weekend I did a 130 mile round trip on A roads and used 20 litres or £19 brim to brim, so its conceivable that 350+ is achievable but I challenge you to stop, start and multiple engine starts then see what you car returns to a tank full. I believe it will be a lot less than 300 miles. I've had as little as 180 miles to a tank all around town with no long runs.

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Old Aug 30th, 2006, 13:23   #12
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I agree Alsner. The only time i have seen 350+ miles to a tank was when i went t le mans this year down the french motorways, we got roughly 350 to a tank. I guess if we were doing 70 instead of 100+, we would of seen around 400 to a tank, but around town, you wont ever get near 350, regardless of how you drive, because i have tried and failed.

Its like people on the CTR forums that say they managed to get around 35-40mpg out of that, its impossible.
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Old Aug 30th, 2006, 14:31   #13
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We have to face the fact that these cars were not designed for town running, they are brilliant tourers and load luggers but will never be economical around town, they are too big and heavy, it's the getting moving that uses all the extra fuel especially if it's all 1st - 3rd gear.

All my SAABs (from single carb 8v, injection 16v and full turbo 16v 175 bhp eat most things on the road for breakfast monster) were the same I would struggle to see more than 18 mpg around town regardless of driving styles.

If it was financially viable I would have a little car for town usage and keep the 740 for runs and family hauling, but those robbing bastards at insurance companies want a fortune because my 9 years no claims is tied up on the Volvo. It would cost me x2 the amount I pay for a 2.3inj for a 1.1 - 1.4l run around. However I will just stay as is because it's the only downside of these cars poor economy around town, they more than make up for this in every other department.

I'll probably get a motorbike with panniers instead as I can insure a 180 mph monster for less than a fiesta or similar and I'll certainly have a lot more fun on a sunday with it.

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Old Feb 3rd, 2009, 13:45   #14
anthony4acre
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Smile Volvo 740 Fuel Gauge

Hi,
I have been a 240 owner for many years & have had just about every electrical fault possible. I just purchased a used 1989 740 Wagon which has many problems like the 240 but worse.
The fuel gauge was the first thing that was wrong with this 740 as it too had a mind of its own & almost left me high & dry one evening.
I suspected at first the sender unit but when thumping the dash board realised the fault was either the gauge or the wiring to the gauge.
I pulled the dash boards instrument panel out & checked this mylar film printed board on the back of the panel with a multimeter. I had downloaded a circuit off the internet & checked the wiring to the Fuel Gauge. Pin 1 ground, Pin 2 Sender wire. Pin 3 12 volts. All the voltages apeared to be stable but whatever I did the Fuel gauge was reading erraticaly.
I removed the fuel gauge from off the rear of the instrument panel by pulling the 3 pin plug & undoing the nut holding the Gauge it in place.
I took the Fuel GAuge into my workshop & connected Pins 1 to ground & 3 to 12volts pin 1 negitive 3 positive & connected a 500 ohm potentiomenter between pins 1 & 2.
I powered up the meter it was a bit eratical & whatever component I touched the needle would either bang on the end stop or go down to empty. When I turned the potentiomenter I couldn't get any sense from where ever I set it.
Next I tried re soldering all the solder joints on the small PC Board & tried again. The fuel gauge was still the same. Still when I touched any componet that had this brown like varnish on it the gauge went silly.
I took the needle & the black circular face plate off the fuel gauge meter
I then decided to put it in a dish with some isopropal alchool & an old tooth brush & scrubbed this brown varnish off the Fuel Gauges PC Board with the tooth brush.
This took some time I then dried the fuel Gauge PC Board with a non lint rag & re assembled the Gauge & connected it up again to my 12volts supply as discribed above.
The Fuel GAuge made a slow move up to the right & by adjusting the 500 ohm potentiometer the Fuel gauge made a slow move up or down, But smooth & not eratical.
I disconnected the Fuel Gauge, reassembled & put back into the instrument panel & put the dash board back together & turned the key & all is working.

Conclusion,
I think the PCB laquer or varnish on the small printed circuit board that makes up the electronics for the Fuel Gauge has become slighty conductive. Which is causing havoc with the circuit as I see some very large value eg 5 mega ohms resistors. This varnish or laquer must have become slighty conductive causing the fuel gauges electronics to go eratical.
By washing off the varnish or laquer fixes the problem.

Cheers
Anthony.
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Old Feb 3rd, 2009, 15:56   #15
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Smile

When I posted on the thread 'What don't you like about your Volvo?', my 940 electrics were behaving and I'd forgotten how tempremental they can be. Right now they're not behaving and nor did they in my 740. Guages and warning lights have a mind of their own. What I've often wondered is that as electrics are clearly an issue in so many models and let down what are basically fantastic cars, why did Volvo never address this issue which seems to run through the 2, 7, 9, series and 300s and 400s and probably many more?
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Old Mar 14th, 2010, 08:11   #16
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Default Isopropyl works

I can confirm the isopropyl fix. I have successfully revived a moody fuel gauge by removing the varnish from the back of its circuit board as described in the previous post. I simply got a toothbrush wet with isoproyl and used it to scrub the varnish off the board. This fix takes only about 10 minutes, and it appears to solve the problem permanently. It should be noted that isopropyl will probably remove the paint on the front of the gauge; so be very careful not to get any isopropyl on the front of the gauge.
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Old Mar 14th, 2010, 08:43   #17
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Default

I had a friend of mine check the solider on the circuit board, he found some loose joints and fixed them, I tried the gauge in and it seemed to work ok, but as I had a working replacement, I just used it.
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Old Mar 19th, 2010, 03:47   #18
webbie1983
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Quote:
Originally Posted by James_N View Post
I kinda sucessfully cured mine!

Mine simply didnt work when i got it. So i got a second hand fuel sender off ebay and had that fitted by a garage. Then i bought a few fuel gauges. The one worked but flicked around a lot, then i tried another one, and that worked ok.

It does go a bit strange round some corners, but for the most part, it works fine, and was suprisingly accurate when i went to france.

Have a look on ebay and around local scrappies, and get a few fuel gauges, fit them, and see where you go from there.

For me, it was mainly trial and error. The second hand fuel sender i knew worked, so i just had to fit fuel gauges untill i found one that worked ok!
who fixed it again :P????? I some what remember leaning in the back of it with a full fuel tank and someones mum outside smoking a fag!
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Old Mar 20th, 2010, 05:52   #19
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I asked a few ago about my gauge giving faulty readings, it seems now that its back working again correctly! The only explaination I have is that the atmospere is now dry, and all seems to well. Has anybody come across this, I have to find which joint is letting in the moisture, is there a connector close to the tank, I havent had time to look yet.
Glad I didnt go to the expense of changing out the complete unit.
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Old Mar 21st, 2010, 11:27   #20
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Default

Quote:
Originally Posted by JohnL View Post
I asked a few ago about my gauge giving faulty readings, it seems now that its back working again correctly! The only explaination I have is that the atmospere is now dry, and all seems to well. Has anybody come across this, I have to find which joint is letting in the moisture, is there a connector close to the tank, I havent had time to look yet.
Glad I didnt go to the expense of changing out the complete unit.
John
I get something like that with my speedo. Once in a while it doesn't move off zero until I give the top of the dash a thump! Almost always when the weather's cold and damp. I don't know if the problem's electrical or mechanical.
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