AlFarkle

Autozone telling me this is an "EVAP system small leak detected"

Tells me to replace the Canister Purge Valve.
Would a dried out cracked hose cause the same problem?

And can someone please tell me where the canister purge valve is located on the vehicle? Thanks in advance.

dave1123

Okay, the way this system works is on cold startup, the Leak Detection Pump closes off the EVAP system and pulls a vacuum on it. If it leaks down within a certain time period or doesn't seal off, it sets a code, either a small leak or large leak. If it holds, the system opens and the Canister Purge Valve cycles to clear any fuel vapor in the canister. The purge valve will cycle as long as the engine is running.

A dried out or cracked hose or fitting, or even a leaking fuel cap can cause a leak. Up until 04, the canister was under the hood on the 4.0, but I've been told they moved it to the driver's side rear side panel just above the fuel tank for the 4.7. It's a real PITA to get to.

A smoke test will find the leak quickly. In this procedure, a smoke generator is connected to the test port (next to the purge valve on the 4.0) and pressurizes the system at 1 psi. Then you watch for the smoke to come out at the leak. If the leak is in the rear, it may take a while to see it.

My mechanic and I couldn't find the leak on my 2000 4.0 until he got a "brain fart!" The TEST CAP was leaking! He put a small o-ring into the cap and the leak was stopped. On mine, it was a small green screw cap on the hose at the purge valve. Because it was the test cap, I had to go thru a "drive cycle" to see if the code would stay clear.

AlFarkle

Thanks Dave. I did some reading on codes and P0456 is fairly common. Most guys say a new OEM gas cap will take care of it. And after further checking with the Mrs., some guy at a parts store put an aftermarket part on it and it turned off the Check Engine Light for a year or so. Since what you describe sounds like a real PITA, go with the easiest and probably cheapest fix first. Thanks again. Jake