Aids HIV FAQ

how to check vacuum leak?

Question:

just brought my car for pollution test and the CO is above standard (standard is 3.5% but mine is 4.26%). if i am suspecting a vacuum leak, how can i check and prove it?

Response:

> … i am suspecting a vacuum > leak, how can i check and prove it?

Make sure the gaskets on the dipstick and oil-filler car are in good condition. Inspect all vacuum hoses for tight fit. The ends tend to harden and come loose with age. The rubber bellows in the air intake system should be inspected for cracks. Leaky gaskets can be found by spraying with carb cleaner when the car’s running. (Yes, there’s a fire danger) The RPM’s should change as the volatile spray is sucked in. You may be able to hear vacuum leaks by using a length of tubing as a stethoscope. If you don’t want to DIY, look for a shop with a Vacutech machine. It pumps pressurized smoke into the engine, revealing the leaks as it comes out.

Response:

Disconnect one hose at the time and listen for change of engine RPM. Vacuum tends to lower RPM when it is operating. No change in RPM -> check the hose more closely. You can also use a vacuum-meter but then you have to know how much vacuum you are supposed to measure. Another trick: If you use startingaid (a spray-box) and spay it around (be extremely careful cause of flamable startingaid) all the way from air intake to the carb./inj.chamber, rise of RPM means "false" air. Vidar (Norway) – Hide quoted text — Show quoted text – > just brought my car for pollution test and the CO is above standard > (standard is 3.5% but mine is 4.26%). if i am suspecting a vacuum > leak, how can i check and prove it?

Response:

Just want to add that: Starting aids which are highly flammable could be very dangerous as Vidar pointed out.  I like to use a spray carburator cleaner.  It is not nearly as flammable, but still will cause the enging RPM to rise when sprayed around a vacuum leak. Rick

– Hide quoted text — Show quoted text -> Disconnect one hose at the time and listen for change of engine RPM. > Vacuum tends to lower RPM when it is operating. No change in RPM -> > check the hose more closely. You can also use a vacuum-meter but then > you have to know how much vacuum you are supposed to measure. > Another trick: If you use startingaid (a spray-box) and spay it around > (be extremely careful cause of flamable startingaid) all the way from > air intake to the carb./inj.chamber, rise of RPM means "false" air. > Vidar (Norway) > just brought my car for pollution test and the CO is above standard > (standard is 3.5% but mine is 4.26%). if i am suspecting a vacuum > leak, how can i check and prove it?

Response:

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