Basically the EVAP test is simple. In your vehicle you have a leak detection pump, a tank pressure sensor and a purge control solenoid and a vent solenoid. To run the test the ECM closes the vent and purge solenoids and the pump starts running. The ECM times how long it takes for the tank to reach a desired vacuum level. It compares that time to a table. If the numbers match up, No code.
If the numbers do no match you get a code based on what did not happen.
In your case you have a big hole somewhere that prevents the vacuum from ever being created in the tank. Smoke test would show it real fast.
Doc is correct stating it would not be the cause of your misfire codes.
Those will either be something like bad plugs, wires or distributor cap, low fuel pressure, dirty injectors or possibly carbon on the valves. Do not ignore the misfire codes, the excess fuel can damage the converter.
When was the last time that engine had a tune up?
Wednesday, January 25th, 2017 AT 12:56 PM