Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Variable fuel readings

Hi guys,

I've got a 75 4/4, and for some reason it keeps changing it's mind how much fuel I've got. It seems to be affected by both engine speed and road speed.

If I'm driving, at motorway speeds, it'll drop by about a 1/4 of a tank. Stop and sit at idle for a minute or so and it rises up again.

Sitting at idle working on something else in the garage tonight, it read fine at 1,000rpm, then started to drop (about a 1/4 of a tank again) and when I put the revs up to 2 - 3,000 rpm to get some heat into the engine it rose again.

Does anyone have any ideas? Thanks a lot.
Tony.

perhaps Volt change?
but look here
http://www.gomog.com/allmorgan30.html#GAS III

A Morgan of that age probably has a voltage stabiliser unit. This is supposed to suppress voltage fluctuations and stabilise the fuel gauge reading.
See item 27 here.
http://www.mgocspares.com/acatalog/mgb_instruments.html#a3189W_2d128484

A solution is offered here......
http://www.britishv8.org/Articles/MGB-Voltage-Stabilizer.htm

Look behind the dash, and if you can locate it, try a replacement.

Having said that, this problem persisted on my MGB even with a new unit, and everything else replaced, and I learned to live with it!

There's a Lucas voltage regulator on my 72 4/4 which serves the instrument panel. When this fouled up the instruments exhibited similar symptoms to yours. I replaced it with a solid state equivalent off eBay which solved the problem.

Great stuff guys, I'll have a bit of a rummage behind the dash.

Cheers.

I had this problem shortly after buying my 1987 4/4. A call to the Harpers advised I check the earth on the voltage stabiliser. Mine was located behind the dash on the right hand side. A clean of the earth solved the problem.
Hope this helps.