Finding and eliminating vacuum leaks (’81 B-150 van… only vehicle i have).

I know that things like the choke pull-off, heated air vacuum diaphragm, EGR valve, and many others are tested to ensure that they hold vacuum for some amount of time, with little or no bleed-down.

I do not know if this is also true for the Air Switching Valve and the Air Pump Diverter Valve on my van. The vacuum connections for these two devices appear to not be holding vacuum for any length of time.

Normal? Broken? If they’re supposed to hold vacuum, for how long? There’s no vacuum holding time test in the factory service manual.

(Both of these were replaced with new parts in 1997/98. If they’re broken i’ll have to replace them again, but if they’re not i’d rather not.)

Thanks.

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1981 B-150 short Van, stock 225, California emissions package, Electronic Spark Advance (digital Lean Burn), Non-feedback Holley 1945, AT
Driven for economy, not for speed.

Without a spec, it's very hard to say exactly how much leakdown is desirable or tolerated. In general, most of those devices ought to hold vacuum for ~1 sec or longer - if it leaks much, you'll never get enough flow through small hoses to have enough vacuum for the device to work properly.

The test is to tee a vacuum gauge at the device and see if you've got enough vacuum for it to operate; if you can't pull 15" or so, it's probably leaking too much to do anything.