Check engine light, not gas cap

[beakster]

2003 cherokee, code0455 large evap leak, replaced gas cap,checked what I could find of hoses. I have a weird slight knocking/tapping noise coming from the area between the gas cap and the rear bumper when the truck is running. Could this be causing the light to come on? Should I be worried about this noise or do they all do it? This light has been on for a year and I have reset it about 10 times. Help?

 

[scottcba1]

Have the evap system smoke tested. A large leak means a hose is probably disconnected somewhere, the canister or cracked or one of the solenoids is stuck open.

-Scott

 

[SteelHeadz]

I'm assuming you meant Grand Cherokee?, 4.0 or 4.7?..The tapping noise your hearing is the Leak Detection Pump located at the driverside rear corner under the bumper fascia. P0455 is usually easy enough to find if it is infact a Vacuum leak from one of the hoses. The only time i would recommend the use of an EELD tester is if all the visual checks has been exausted with the lack of a broken/ cracked vac. lines, the EELD machine will help aid in isolating the leak internally from either the Leak detection pump , Purge solenoid or the vapor canister. Check all the Vacuum lines from the intake manifold specifically the one with a valve that has a green cap. This is the test port for the Evap. system. Follow this line all the way to the rear of the Jeep. You will find at least a couple of rubber line splices along the line. These rubber hoses usually crack and enables a leak for the DTC to occur. Replace the one's you find faulty with an approved emissions hose and keep looking for more all the way up to the Evap. canister and Leak Detection pump.

 

[beakster]

Thanks for all the info! I will trace all of that out this weekend and see what I find.