Why get a vacuum gauge...
 

Why get a vacuum gauge if I already have an mpguino? Is it beneficial or is my money better spent elsewhere?

Well they can be had for ~$10, I never figured out how to use it effectively but I really really liked the responsiveness of an analog gauge.

I use my vacuum gauge as my primary instrument and then confirm its benefit with the MPGuino. Keep the vacuum as far away from 0 as you can (within reason, you'll see) and then see what the MPGuino is telling you. You do have to compromise on hills and during accelerations but you get used to the instantaneous info. It is a great way to gauge where your throttle position needs to be once you are used to it and the drive you do most often. Another trick is when you are driving at constant speed and power like on a long stretch of road. Lift you foot just ever so slightly and see the response on the vacuum gauge. You end up at the same speed but more vacuum and less fuel used.
I love mine!

VACUUM gauge = old-style, proven, analog, fuel-economy display device.

MPG Gauges = new-style, proving, digital, fuel-economy display device(s).

...best of "both" worlds!

I haven't been around for quite a while, because I did the impossible (almost) and empowered my humble Fairmont wagon with a full set of 1984 Mustang gauges, including the Trip meter, and then added a voltmeter and vacuum gauge. Now I can see what the engine is doing and catch fuel usage changes by the tankful.

Here's some of the things that a vacuum gauge will tell you:
Vacuum Gauge troubleshooting

If you're a Ford fan - click on the combo box for some tech info:
efv8 - Tech Tips

What I like about that graphic (right-click and save picture as...) is that it prints out into a small enough page for the owners manual. Handy on the road.

This one shows one dynamically through 15 different conditions:
How to Use and Interpret a Vacuum Gauge

Another downloadable chart for GMers:
Reading your vacuum gauge

A decent bit of tech detail about the Vacuum gauge:
Using a vacuum gauge

My car doesn't have all the bells and whistles for a Scanguage or other Hi-tech monitoring. In fact, because it was built in Mexico, it didn't even have Electronic ignition. After upgrading to a freshly dealer-rebuilt 3.3L I6 and transmission, it finally matured into the E-age.;)

After seeing all that a Vacuum gauge tells me, I wouldn't own a car without one! It's the early OBDII, as far as I'm concerned.

That goes for the voltmeter too. Up here, in the cold Canadian Prairies, your life depends on the charging system. The Ammeter just tells me how much the car is using. The Voltmeter tells me the system is charging, good, bad or not enough.

Stormin' Norman -

Thanks for the post. I think of the vacuum gauge as a "heart monitor" for the engine, not just an old-school MPG device.

CarloSW2

I like using a vacuum gauge with the MPGuino. It is interesting to see the changes in fuel flow despite the fact I do not change throttle position, but the vehicle shifts (or something else happens). Watching the vacuum gauge also helps me determine when I am getting a slight wind break from vehicles ahead of me (if the cruise control is engaged).

If you're like me and also trying to get the most possible miles per car, then you may be driving something with not a lot of electronics for the mpguino to hook up to. Vacuum gauge, Mk I eyeball, Foot 1 and Foot 2 are all the instrumentation I've got.

...think of a VACUUM gauge as a mechanical intake-SPIROMETER for your car.

...SPIROMETER is an apparatus for measuring the volume of air inspired and expired by the lungs.

I'd use it to look for thumps at speed (shaking needle)...
and unusual low at idle. That is about it. I do not keep one hooked up.