I have a 2005 F350 with the 5.4 motor. I have a P0446 code that will clear with the scan tool and return within 10 miles. I removed the solenoid, there is 12 volts to it with the key on. The solenoid shows 55 ohms. The solenoid closes when I apply positive and ground to it. I can blow through the solenoid and vent without restriction normally. When I blow into the canister or apply compressed air, it creates good pressure.

I have two of these trucks, the other truck does not have the P0446 code and using the gas cap and solenoid from that truck still generates the code.

I am thinking that maybe the problem is on the vacuum side or the ECM.

I am not getting any other codes, so not really sure what else to try.

The truck runs good, but I noticed that it gets rough when the accelerator is pushed to the floor, but when you let up a bit, it smooths right out.

Where is the ECM located?

Where do I find the vacuum source that the evap system uses for the test?

If I had a vacuum leak, wouldn't I have more trouble codes?

 

The code did not return during a 25 mile drive. Maybe I get it beat.