Practically Classics Forum

Hi,
I've stuck on this for ages! The fuel guage on my MGB is very erratic. When i turn on the ignotion it reads about a 1/4 full. Then, on starting the car it will go to full. Once choke is in and driving around, how the the reading goes depends on how high the car is revving. 60mph gives me a full tank. 30mph is half a tank etc! Anyone got any ideas. I had a new voltage stabiliser put to cure a similar problem. Could my garage have wired it incorrectly? Also my fuel sender is fairly new so I dount this is the problem?
Any ideas would be great- thanks everyone!

If the gauge is changing reading depending on how high the car is revving it is almost certainly a dodgy voltage regulator. Fitting one is only one screw and 2 wires, you can't really get it wrong but the do go faulty.

Probably yet another example of the appalling quality of after-market parts, especially electrical ones. This means that these days you simply cannot eliminate a component just because it's new. As above, probably (to the point of being almost certainly) the voltage regulator, but as I say, don't discount the sender just because it's new either.....

At least the sender unit is easy to test off the car.

Do check all the instrument and sender unit earths too.

Testing the voltage regulator is easy if you have a multi-meter. Connect your meter between the output from the regulator and earth. It should give 10 volts with the ignition on regardless of whether the engine is running or the revs it is running at.

edit: thinking about it, if it is an older regulator it will be a bi-metal strip so you may see the voltage rapidly bounce between 2 and 10 volts but if it sticks at a particular level for any length of time or goes above 10 / never gets to 10 it is duff.

My old VW use to read fine but never below 1/4 turned out the gauge had a bad earth.!

I had a similar problem with my 69 GT, I bought a new old stock voltage stabiliser , fitted it and still had dodgy volt readings. I had fitted a new sender unit, another gauge and even slave wiring and still my fuel gauge was giving me erratic readings. I then decided to try a solid state stabiliser because the contacts in the old stabilisers, even though new were ancient . The solid state one with no moving parts inside fixed the problem straight away. Solid state stabilisers are available on E - bay for very little money. good luck stan

The solid state ones can be bought in Maplins' at under a Pound each (94p last year) for ten. Time for a mass forum purchase maybe?