[KULTULZ]

Originally Posted by Daves55Sedan

Tell ya what. There's a ton of ways to check the vacuum booster on the fuel pump. You could start the engine, throw a bucket of water on the windshield,

You mean just the water, not bucket and water?

...turn the windshield wipers on and rev the engine with brake pedal depressed. If the wipers STOP when you rev the engine, the vacuum booster is shot.

Not necessarily. There may be an interrupted vacuum signal or a mechanical defect somewhere.

Also, if I didn't mention it already, another easy way to check is to disconnect both lines connected to top of vacuum booster. Plug one side and use a MityVac (no need to have engine running for this test). Pump the MityVac trigger a couple times to reach a couple inches of mercury on the guage and hold it like that for a few minutes. If the guage does not drop to zero, the booster is likely good. Just don't exceed the maximum vacuum output of the booster or it might result in damage.

The quickest way (IMO) is to disconnect the manifold vacuum source and put a vacuum gauge on the outlet port. Without the manifold signal, the vacuum pump will initiate and supply a vacuum signal (min 10hg) If low/no signal, you would go further into it. The vacuum pump initiates a signal on both strokes so there should be no interruption of signal.

Originally Posted by Daves55Sedan

I have major doubts that the fuel pump vacuum booster is at fault, but checking is a good idea. Reason why I don't think it is the problem is because you still have normal engine vacuum (albeit flowing thru the booster) and feeding your accessories.

Any accessories are supplied from the wiper vacuum circuit. The booster is on a separate circuit.

You should still have plenty of vacuum to operate wipers and heater controls (unless or hose or component is faulty) as I pointed out previously.

Remember, not all engines were equipped with the dual action fuel pump to begin with.

Proper operation also depends on state of tune and having a normal/steady manifold vacuum @idle.

READ HERE -

https://www.ctci.org/windshield-wiper-vacuum-source/

https://www.ctci.org/improving-winds...iper-function/