I have a '96 F-150, 4.9L with an OBD II code of P0443 (EVAP purge valve) problem that I cannot resolve. I have already changed the purge valve,and checked the vacuum lines to it; they seem to be ok. I am wondering if the new valve I installed (Motorcraft CX-1549) might be faulty. Is there a way to test it or anything else I should look for with this problem?
Thanks!

 

Use a voltmeter or test light. With the key in "run" but engine off, there should be 12 volts to both sides of the solenoid. If one side has 12 volts, but the other does not, you have an open solenoid.

If both sides have 12 volts, try the following:

With the engine warmed up, advance the throttle to get about 2000 RPM. One side of the solenoid should go to 0 volts. If it does, the electrical control is OK, if it does not, the computer may not consider the conditions appropriate for cannister purge -- or there may be a wiring problem.

With the engine running, verify that there is vacuum present at the valve input.
If you can chase the wiring diagram, find the "low" side of the solenoid, deliberately ground it, and see if the valve opens (and there is vacuum on the output).

You aren't getting code P0440, which is what I should think would be flagged if the solenoid were bad. You also aren't getting code 442 or 446, which would mean a non-air tight fuel system. Still, check your gas cap to make sure it is on tight and not damaged.

One test you might do on the valve is to remove it from the vehicle. Apply vacuum to the inlet side of the valve. It should hold. Connect 12 volts to one side of the solenoid, ground to the other. The held vacuum should be released. That is basically all there is to the valve.

Unfortunately, OBD-II is less ammenable to back-yard repairs without a scanner than is OBD-I. I just don't know enough about it to offer anything further.