Ducman82

i have a euro dash in the garage, and it has what looks like a fuel economy gauge. the back of a US cluster looks like it could have one. did they ever make that?

Tom. M

My 82 dash has one..

928 obsession

Both of our US '82's have a fuel economy gauge as does our US '85 S I do not remember off hand if our S4 does.

Ducman82

i wonder it that is just a Tach "cluster" replacement for one that has that option... do they work well?

928 obsession

All three of ours function on the cars, but I would take their accuracy with a grain of salt. To be honest if your new cluster lacks the gauge I would not worry about it, the gauge is somewhat pointless.

Tom. M

I believe it's just a manifold vacuum gauge..simple..less vacuum (eg open throttle)...worse fuel economy LOL

dr bob

It's smarter than just a vacuum gauge but not by a lot. Watch yours and see that it goes to zero when the car is stopped, where a vacuum gauge would go high on decel then midrange at stopped idle.

tveltman

Do we know what sort of input the gauge takes? Is it 0-5V?

Z

The MPG gauges get their signal from the fuel injection computers. It's the same 12 volt square wave signal that gets sent to the injectors to fire them, and the gauge is basically like an injector duty cycle or pulse width meter. A longer pulse or duty cycle means that the injectors are opening for longer, delivering more fuel, and you're using more gas.

Tom. M

the old ones too? I know the one in my GT does that..as I get awesome fuel economy with the 24lber's in there .. (actually the pulse width is less with the 24s over the 19's so it "seems" the fuel economy is better..but actually it's just reported better).

the fuel gauge in my 82 dash is not hooked up since I've got a 91 S4 engine in there with Megasquirt ...

Vilhuer

Early models used vacuum based system which has IIRR sort of computer which does some calculations to make system better than just basic vacuum gauge. Later MY use injection pulse width.

dr bob

The later cars with digital dash use injection pulse width and the speedo pulses to come up with the integrated fuel consumption number.

tveltman

So on the older cars the actuation is literally a square wave PWM? I'm not terribly familiar with this sort of electronic stuff, but if I were to pulse a 5V signal instead of a 12V signal, how would that change the gauge function? Would it just not work, or would it accurately measure pulse width?

Thanks!