MPG Gauge not working - E30 316

[daytona]

The "current MPG" gauge has suddenly stopped functioning on my '88 E30 316 (Weber Carb - 1797cc). Does anyone know where the sender unit to feed the gauge is located please? Or is it run by vacuum from the carb? There is a little "valve" with a vacuum pipe going to it and a 2-pin plug, at the centre of the bulkhead. Could that be where the reading is taken from by any chance? Any help will be greatly appreciated thanks

[Si316]

I think it takes a signal from the original pierberg carb. All the time mines had a weber carb on the guage hasn't worked. unless i am only gettin 15mpg lol

[daytona]

Thanks Si, but it was working with the weber carb when I got the car, then all of a sudden it packed up. The needle moves when ignition is switched on, then goes back to 50 MPG+ (I wish!).