rustang222

I'm stumped. My truck is throwing a P0451 code for the EVAP system. When I went to Autozone just to get the code pulled the guy said that it was likely my fuel cap. I then had a friend run a complete diagnostic on the truck with his fancy scanner and nothing specific came up. He cleared the code and I drove home without any issues. I even stopped the engine and started it again without the light coming on. THEN I left it sit overnight in the garage and when I fired it up in the morning, the light was on again throwing the same code.

I've done this a few times now: clear the code, drive the truck throughout the day without any issues, let it sit overnight, fire it up and the light is back on. Anyone have a clue what might be going on?

My last question is related to the EVAP system in general. I just changed my spark plugs and am wondering if there is something in the engine bay that I may have jostled loose while working on the plugs. Anyone have any thoughts on this?

JByrd825

First thing first, replace the cap. They're cheap enough and sometimes their one-way vent does fail with age and they cause a pressure leak. That's the easiest of fixes you can do, and if that doesn't work...you're in for a process that's a little more extensive.

If there is a leak in any hose in the system, or in the charcoal canister, trying to track it down without the aid of a smoke machine is basically futile. The machine lightly pressurizes the fuel tank with smoke and any leaks will be made present. If no leaks are present, then it's possible the purge-valve is shot and needs replacement.

rustang222

I'll give that a shot.

Do you think the fact that my CEL came on right after doing the plugs is coincidence? I'm just trying to rule out anything that I could have jostled loose in the engine bay.

JByrd825

I would like to say that's it's just coincidence. Wouldn't be the first time coincidence has been a b*tch.

rustang222

No dice with the gas cap switch. Time to take her in to the shop...