Taking a Walk in the Outback
Join Date: May 2011
Car Year: ...
Car Model: ...
The EVAP system monitor checks for fuel vapor leaks by performing either a pressure or vacuum test on the fuel system.
For 1996 through 1999 vehicles, the federal standard allows leaks up to the equivalent of a hole .040 inches in diameter in a fuel vapor hose or filler cap.
For 2000 and newer vehicles, the leakage rate has been reduced to the equivalent of a .020 in. diameter hole, which is almost invisible to the naked eye but can be detected by the OBD II system.
Finding these kinds of leaks can be very challenging. According to one expert, you can find a .040 in. leak with an ultrasonic leak detector but not a .020 in. leak. For such a small leak, you will need a smoke or dye-type detector.
Choices here include ultrasonic leak detectors that listen for sound waves produced by air or vapors escaping through an opening, smoke detectors that generate smoke which allows leaks to be spotted visually, and dye detectors that use a visible or ultraviolet dye to reveal leaks.
Last edited by Georgie; 11-06-2011 at 08:36 AM.