Date: Tue, 16 May 2000 10:33:59 EDT
Reply-To: Wolfvan88@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Robert Lilley <Wolfvan88@AOL.COM>
Subject: Vacuum leak sources
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Here are some areas to look for leaks. Rubber parts are getting old and can fail. YOur engine might be "running good" but there could be a leak going on.
The following are various sources of vacuum leaks. Once a leak starts the engine starts to run lean, the O2 sensor will enrich the mixture to it max. If the leak is more than the o2 max, the engine starts to run hotter and further deteriorates the worn rubber parts increasing the leak and further leaning the engine to the point of overheating and other running problems.
When the engine is cold, the leak will cause the engine to stall because the volume of air is to lean to support running the engine. The idle circuit is running in default with a set amount of fuel and ignoring all sensors until it is warmed up.
I discovered this be reusing the throttle body gasket after removing the TB to adjust and clean it out and check the shaft air seals.
It resulted in decreasing the amount of vacuum by allowing un-metered air to enter the system. The air decreased the amount of vacuum the engine could build. The following the effects:
1) The cold idle cut off returned (I had replaced the idle control module, $175, my Idle control module was damaged due to a short in the hall sensor wiring harness)
2) The amount of vacuum to control the fuel pressure regulator will decrease.
3) The engine can have a hesitation when the throttle was pressed.
4) Increased fuel consumption.
5) Poor running engine.
6) Damage to the engine.
Various sources of leaks:
Air Runners:
Intake gasket- head to air runner
Small injector seals
Rubber boots around runners and center plenum
Leaks where the tube is pressed into the ends
Center Plenum:
Fuel Pressure Reg mount
Throttle Body gasket
Idle speed valve rubber boot
vacuum line from fuel tank vent system
Throttle body:
Butterfly Shaft
Seals on shaft cracked
Vacuum for fuel tank vent system
Air intake elbow
Air intake elbow:
Cracks in rubber tube
Engine breather tube
Idle control valve rubber intake tube
Valves too tight:
This causes a leak and decreases vacuum at idle and low speeds.