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

[belugablack]

I know that many 740s suffer with this, but is there a proper cure for an occasionally dodgy fuel gauge, i.e. one that can flick from full to empty and then settle at midway before flicking about again. It works OK sometimes but I am not good at watching my mileage and calculating how much fuel I have probably used.

Is it likely to be the gauge itself at fault, something more complex behind the dash,or a sender etc etc and is it an easy fix?! I have seen quite a few cars advertised with faulty gauges that I wonder why they haven't been fixed.

Has anyone successfully cured theirs please? Is it almost definite to be one thing, or could it be that I get a new sender only to find I need a new gauge, and then maybe it was something else all along type of malady! In which case should I grin and bear it?!

All help gratefully received!

Daniel

1990 745 GLT

[James_N]

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!

[BillB]

You can test for a sender fault with a multimeter. The sender wires are accessed via the left hand pull-out section in the cargo area of an estate (I forget the colours). Haynes gives resistance values for different tank levels. A reading of infinity ohms (or intermittently infinity) suggests a faulty sender. If it seems OK, suspect the gauge, which typically has dry soldered joints. You have to remove the gauge and investigate. Typically, the printed circuit connections fail or the metal posts that connect the gauge to the circuit. Regards.

[wispa]

The girly and no-tech answer is find a bump or hole in the road and drive over it, that normally sets it working - that's how I work with my erratic gauges! Both fuel and temperature are suspect on mine.

Also - if you don't think you can trust your fuel gauge, why not refill every 250 miles (use your trip meter and reset to zero every time you refill. ) Then you have a way of double checking the erratic gauge.

[James_N]

250? I really struggle to manage that around town with my 2.3 petrol. Dont forget, yours is a diesel, and the OP's car is a petrol

Id say 200 miles to be safe.

[740Estate]

I used to get 250 out of my 740 when it was filled to the brim to start off with, but yeah go with 200 for safety's sake!

[James_N]

i can get to 250 but i think for safety sake when you dont have a fuel gauge, deffo go for 200. I remember when my fuel gauge wasnt working, The car started coughing badly and even cut out at one stage doing round a roundabout Managed to get it the 4 miles back home. God knows how

[wispa]

I was thinking of 250 miles becase my 740 2.3 used to get refilled every 240 miles and thought you might have a marginally better MPG than my old car. The petrol gauge didn't work at all. I averaged about 24 MPG but only had her for 3 months before the piston slap and other repairs required for MOT meant she became uneconomic to repair. My diesel goes for 400 miles on a tank!

[old740]

How about 350? If my '88 740 has a 13 gallon tank, does 29 mpg overall and you allow for two galls always in there.....that gives arange of 350!

[Mudhook]

I can't get my 740GLE 2.3 to drop below 350 miles to a tank, and I have seen over 390. My earlier 87 2.3 ran 400 a tank every time and once 420. Do you guys have lead feet?

A dose of injector cleaner, a clean air filter and gentle driving habits should get mpg up to well over 30.

Regards, Mudhook.