I have a 2011 Mustang 5.0 and put a Boss 302 intake manifold, JLT cold air intake, Borla S Type catback exhaust on my car. I had it tuned at a local mustang shop. After it was tuned I drove it for less than a week and I got a check engine light. When I hook up and read the DTC it gives me a P0456-evaporative emission system leak detected (very small leak) 0.020". So I talked with the shop that tuned my car and they said they can delete the code so it doesn't come on. My problem with that is if something is really broken I wouldn't know it. Is there something that I have over looked that could be broken?

 

Welcome to the forum. Look at the evaporated line running into the intake. Probably not on good or got cracked when it was messed with.

 

First off thank you. Second is that the line that runs to the check valve and then the intake? Also why would it happen intermittently? Because I can reset the DTC and it takes a day or two to come back.

 

Evap is a slow to set monitor. It can only set when certain conditions are met.
The gas tank has to be between 1/4 and 3/4 full, the fuel tank pressure has to be at a certain pressure before evaporated will even begin running its checks.

Evap is emissions related. It will not effect the running of your car. It is there to keep the fumes in the gas tank from entering the atmosphere by sucking the fumes into the engine to burn.

You can tune evaporated out of the programing and be just fine. The only thing you might notice is pressure in the tank when you try and fill it.