MPG aids
 

Back in 1975 we bought a Ford Pinto with the V6 engine and automatic. In the dash was a light that got brighter as the MPG improved, that was actually a simple vacuum gauge. This was shortly after the 1973 oil embargo. For years I have had a vacuum gauge mounted in my dash for that very purpose. Manifold vacuum is a great way to keep your foot from wasting gasoline. Driving while keeping the vacuum as high as possible is an easy/cheap way to save gas. Trying to get as much economy out of my 2.3 is priority one, and I already have a vacuum gauge I will put directly in front of the driver. I am sure most on this site already know this but it never hurts to restate easy fixes.

Same idea as running an MPGuino or other MPG gauge on a more modern car...if you know what the engine is doing, you can - if you choose - get the most out of it.

Been a while since I've heard of anyone using a Vacuum gauge, but it would be the tool to use if you were running a carb!

I always liked the idea of a 5 or 6 inch diameter gauge on the rear firewall of a VW Beetle. That would keep the vacuum line short and it would be readable in reverse in the rear view mirror.

The XFi has an Eco-light that comes on to prompt you to short-shift the gears. I don't know the logic of it, it certainly doesn't tell you when to downshift.

How/when is the vacuum gauge used really?

I'm thinking on highway cruise for example, without a gauge you'd give it enough gas to not lose speed, what would you do differently if you had a gauge to look at?

vacuum gauge use
 

As the throttle is opened on a carburetor engine, vacuum drops, and as the throttle closes vacuum increases. So, if one watches the gauge drop as the car accelerates, a slight decrease (backing off the throttle) can still give the acceleration needed but drop fuel consumption. Consider it the "sweet spot." Also, once the car reaches the desired speed, vacuum increases due to a drop in engine load. Driving at a given speed on level roads keeps vacuum high... therefore higher MPG. A vacuum gauge is an excellent tool for tuning a carb. motor, and I assume a throttle body that uses a throttle plate to control air-fuel mixture. A vacuum gauge can tell engine problems like bad valves, manifold leaks, bad carb gasket sealing, and dwell setting, plus more. Once it was a necessity in any garage/shop.

One picture can be worth a lot of typing:

https://cdn.shopify.com/s/files/1/16..._1024x1024.png
https://cdn.shopify.com/s/files/1/16..._1024x1024.png

Vacuum gauge
 

The Pinto had a rectangular light on the dash that got dimmer as MPG dropped...I think. I know it was a brighter/dimmer light not an analog gauge. Anyway my wife really liked it because she did not need to know how to read a gauge, but a light that changes with MPG was easy.

IIRC nowadays most instruments are electric, with remote sensors instead of keeping pressure, vacuum or whatever inside the vehicle.

I rented a box truck with this nice gauge.
https://ecomodder.com/forum/attachme...1&d=1604800197

My Insight came with a lot of instrumentation: Lifetime fuel economy, Trip 1 fuel economy, Trip 2 fuel economy, Current fuel economy (avg since button reset, usually at the start of driving), and an instantaneous readout. There's also a battery charge/assist gauge and battery level.

After changing my engine out, I now have an MPGuino which measures the injector pulses and gives an extremely accurate gallons per hour and MPG figure. I also have a bluetooth connection directly to the ECU which gives anything else I want through an app on my phone. I commonly used it to see degrees of ignition timing, intake and coolant temperature, vacuum, throttle percent, and air fuel ratio (measured vs requested).