Hello All

Amongst the three instruments found in the center cluster of a car at the wrecking yard, is a Fuel Economy (Vacuum) Gauge. I connected a T-fitting to the Vacuum Reservoir, but the Needle Remained pegged and didn't waiver, even after I shut the engine off. When I disconnected it, the needle went to the Red (No Vacuum). I connected the Gauge to a nipple on the Intake Manifold. The needle waivered, as I played with the Throttle. Does that mean that I have to run a hose all the way out through the firewall and to that nipple or one on the Carb, just behind the Throttle Plate, or is there a fancy way of connecting it to the Vacuum Reservoir?

There was also a Voltmeter and an Outside Air Temperature Gauge. I installed the Large Tachometer and Small Clock. I discovered the Speedometer Cable had its original Lock in place. I suspect 150,500km are the true mileage for this 1981 244DL B21A. I am, as yet, undecided if I want to install the other gauges, because I like the small cubby hole to put sunglass case, cigarette lighter, when I am charging my mobile (cell) phone, etc.

All recommendations and information about connecting the Fuel Economy Gauge will be appreciated. Thanks.

Oh, as a side note, my electric antenna, broke, when I was lowering it . . . with out warning. It had been working perfectly and the antenna elements were clean and lubricated. Fortunately, I have a spare insert, from the wrecking yard, but not looking forward to repairing it. Usually, I only like to do a job once and 110% the first time.

There is a check valve (one-way valve) between the manifold and the vacuum reservoir -- this ensures that your climate system (flaps' motors) has a vacuum supply despite fluctuations in manifold pressure (which is normal, in the course of varying throttle, engine load and engine speed).

If you use any point downstream of the check valve, your gauge will only show reservoir pressure.

For a useful economy gauge indicating engine conditions, you need to use a point upstream of that check valve, meaning at the manifold for greatest accuracy (the narrow hose dampens small fluctuations.

Did the gauge cluster come complete with the sensors and wiring? – makes it much easier to fit.

to get an acurate reading you need to pickup the vacuum before both the tank and the one way valve. I installed one and put a splitter near the throttle body.

Thanks, Yama . . . I suppose that would be somewhat difficult, with the Zenith-Stromberg Carburetor. Any suggestions? Also, what should the indication be for optimum mileage?

I guess in that case anywhere on the intake before the oneway vacuum check valve would work ok. The check valve and the tank work together to keep the vacuum level in the tank at maxiumum to operate the vacuum operated valves. The gauge I have mileage is best when the needle is to the left and worst in the red area to the right.

Yama,

Thanks. Any idea how much vacuum or the range of vacuum "pressure" between beginning of Red and all the way to the left?

The vacuum gauge is a LOT more useful than just a measure of vacuum -- it indicates how things are working in the engine. In other words, a great diagnostic tool.

Read this links:

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm
http://www.secondchancegarage.com/public/186.cfm
http://www.mazda3forums.com/index.php?topic=173816.0

Hope this helps.