Vacuum Gauges

Is it practical or useful to have a vacuum gauge in the trucks of today? I know older bigger trucks had them standard. And I’ve read how you can put them in a vehicle and watch how much gas you are giving it, and hopefully fix your bad habits and get better gas mileage.

I recently put one in my 1999 F-150 with a 4.6 and a 5 speed, hoping it would help me out a little bit. It shows me all that I mentioned above, but there is nothing I can change driving-style wise after watching the gauge. This truck just doesn't have enough power I don't think. If I kept the gauge in the "green" zone (above 12) then I don't think I could hit 40 MPH. I usually shift between 2100-2500 RPM, and aim to keep it above 1400.

So, any experiences with vacuum gauges in newer trucks/vehicles?

Thanks

(quoted from post at 17:51:44 02/25/09) Is it practical or useful to have a vacuum gauge in the trucks of today? I know older bigger trucks had them standard. ......

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The vacuum gauges on older trucks were generally connected to the brake vacuum booster system. There purpose there was to warn of brake system failure.

On carbureted vehicles, when you lug the engine, the "load enrichment circuit" (power valve) opens to allow extra fuel into the mixture, and MPH rapidly goes to hell.

With modern fuel injection, the oxygen sensor provides feedback, so even while lugging, the 'puter dumps only the necessary amount of fuel into the mixture.

So, watching the vacuum gauge isn't as important as it used to be in the carb era, as a "closed loop" engine can lug in overdrive and still get good mileage.

I put one in my 94 Honda Civic del Sol when I had it... I found that as long as I didn't give it enough gas to get below 5" of vacuum it would improve mileage.

The important thing to me, is that keeping it above zero should help economy. Once there is zero vacuum, the engine is working about as hard as it can, and more throttle will just use more fuel. This may or may not be true on a newer vehicle that uses a Mass Air Flow sensor (MAF) to adjust the amount of fuel...

Try driving it for a few tanks, keeping the gauge at 5" or higher...

My '65 Comet had a vacuum gauge from the factory. Really it didn't tell you anything you didn't already know. But it may have been useful for economy because in theory you could keep the power enrichment circuit from opening. Makes no sense in a modern engine with electronic fuel injection.

It's a simple fact that a gasoline engine is most efficient at wide open throttle, and the lower the rpm the better. In other words, lug the crap out of your engine. Which is exactly the opposite what a vacuum gage will tell you to do.

Ya, it seems to be really content at 5-10. About 47MPH, 1400RPM in 5th gear, barely accelerating/cruising, and it is at 5 just cause the RPM's are so low and it the engine is actually working. Getting below 5 takes a noticeable amount of acceleration.

Thanks. That basically confirms my observations to this little science experiment lol

To further the discussion concerning more modern vehicles with fuel injection... I run my ScanGaugeII in my 01 Honda Accord from time to time to help my driving habits. http://scangauge.com/

I usually set the gauges to instant fuel economy, MAP (Manifold Absolute Pressure) sensor, LOD (Load), and the coolant temp. I have found that while cruising on a level stretch of road, I can adjust the gas pedal to get up to 10 more miles per gallon and still maintain the same speed. I'm not really sure how this is possible, but I trust the gauge as I have checked its trip computer against my actual fuel usage several times and it is accurate.

Another way I've increased my fuel mileage with the ScanGauge is to only accelerate to 50% load - only working the engine half as hard as it could be. It takes a bit longer to get going, but is worth a couple MPG in a week of commuting to work.

One time I noticed my mileage was quite poor over a couple of tankfuls... like 5 mpg or more short of my normal efficiency. I went over the car carefully and discovered that one of the front brake calipers was stuck and dragging. Took it apart, cleaned it, and made sure the rest were loose and got my mpg back.

Some more simple mileage tricks: keep your tires properly inflated, I've found that here in AZ about every two weeks I can expect the tires to be 1 to 3 psi low. Don't carry extra weight you don't need - on long trips I take some spare parts, hoses, extra fan belt, and tools... but around town I don't need all that so I unload probably 50 lbs worth of stuff. Lighter = easier to accelerate. Don't waste too much time on the morning warm-up - modern gas engines really don't need more than a minute before you start driving, just don't go for redline or hard acceleration until it's fully warmed up. And actually, most new computer controlled vehicles will limit things to avoid damage until they are warmed up, anyway. Same deal with cool-down, just driving through town or on the highway with a gas engine doesn't work it hard enough to warrant a cooling-off period. Most modern diesels don't need much cool-down, either when not worked hard. Even after working a diesel pickup, a minute or so is plenty to cool the turbo. And the last thing I can think of right now - the best efficiency in most vehicles is obtained around 60 mph, so slowing down a bit on the freeway/interstate could save a buck here and there. I know some places it would be suicidal to drive that slow, though.

FWIW: Under ideal conditions I have attained 36.9 mpg with my 01 Honda Accord 4-cylinder, and around 27 mpg with my 97 Grand Caravan v-6...

Disclaimer: Just my opinions and experience with my limited time on earth. YMMV (Your Mileage May Vary)