Basically, the amount of vacuum in the intake manifold varies with how much the butterfly valves(either in the carby, or in the throttle body on a fuel injected engine)is opened. If you take your foot off the accelerater, the engine is trying to suck air past the partly closed butterfly, thus creating vacuum. If you are under acceleration and the butterfly is open, the engine is drawing air freely, so manifold vacuum is low. Turbocharged engines have lower vacuum because the air is force-fed, so an electric vacuum pump is sometimes used to run the brake booster.
On some of the older vehicles the vacuum modulator controlled the shift points of the transmission by using the vacuum supplied from the engine.
no a diesel does not produce vaacuum when running. but vehicles that require vacuum for the brakes have a vaccuum pump attached to the engine to supply the needed vaccuum
You must have a diesel. The vacuum pump is what gives you POWER BRAKES and on the newer engines it also makes the power steering work. Only a gas engine makes vacuum. A diesel engine does not make vacuum, so they install a vacuum pump.
A vacuum leak in the vacuum supply line from the engine can do that. Many vehicles use engine vacuum to operate the HVAC system. If there is a loss of vacuum to the system it will default to defrost.
The vacuum that operates the doors for an ac system is created from the vehicles engine. Check under the hood for vacuum lines that have cracked or have become disconnected to start.
they work off the engine vacuum through hoses.
Well, a transmission itself does not idle...the engine does. A vacuum leak in the engine will cause faster idling or slower idling depending on where the leak is. Newer transmissions do not use vacuum at all for their operation. Older vehicles used vacuum to help with the shifting of gears-automatic transmissions.
Not knowing what vehicle you have, many vehicles use a vacuum supplied by the engine to operate the different positions for the air to come out. When the vacuum is absent the system defaults to the defrost mode. I would check the vacuum supply hose starting at the engine for cracks, damage and disconnection.
On modern vehicles the brake system is enhanced by a vacuum operated "booster". This makes the brake pedal softer and more responsive. When the engine is turned off the engine no longer produces vacuum to supply the booster so the pedal gets hard.
Vehicles made in the USA have a diagram on a sticker located under the hood in the engine compartment. The sticker shows the routing of the emission related vacuum lines. Vacuum lines ae connected to the inlet manifold at one end, to work on the depression at this point. There are several ancilliaries that may work off this, the most popular being the brake servo. Also sensors for the ignition (advance and retard), vacuum servos for 4x4 control, computer management box and emmision controls.
We have fleet vehicles at work with the 4.3L engine and several of them are well into the 200K and running strong.
think of it as a battery. it stores a large vacuum reserve while the engine is running. then its used whenever you use the device attached to it requiring the vacuum source. without it things like your heater and ac controls would not work properly because they require a large amount of vacuum to operate that your engine alone cannot supply fast enough.