Question about 2002 Jeep Liberty
Replaced bad muffler, welded hole in manifold pipe, replaced bad vacuum line off charc. canister and replaced bad ground on fuel tank still getting code. any ideas?
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Posted on Jan 02, 2017
YES A CAP FROM THE DEALER WILL MOST LIKELY SOLVE THIS ISSUE...SOME OF THE AFTERMARKET CAPS ARE NOT MADE TO THE PROPER SPECS TO MAINTAIN PROPER PRESSURE/VACUUM ON THE SYSTEM WHEN THE EVAP TEST BY THE COMPUTER OCCURS
Posted on Aug 31, 2009
Testimonial: "Thank you- I'll try that."
I had the same issue with my 4.0, I went through all the same BS you did and in the end it was a faulty fuel pump. Pricy i know but im sure thats your problem
Posted on Nov 15, 2009
I do not know the codes but after a smoke test ,I would use the codes and a schematic to walk down and test every switch or valve in the EVAP System. A professional scanner would be nice,so you could command somethings on and off.
Posted on Mar 12, 2010
Tips for a great answer:
EVAP Vent Control Solenoid Circuit Malfunction
Vent solenoid circuit open, shorted to ground or to power (B+).Vent control solenoid is damaged or has failed..PCM has failed.TSB 00-060 (7/00) contains information related to this code.Trouble Code: P0455
EVAP System Gross Leak (0.080") Detected
.EVAP control system pressure sensor is damaged or has failed.EVAP purge solenoid or canister vacuum line loose or off.EVAP purge solenoid is damaged or has failed.EVAP emission canister is dirty, restricted or full of water.EVAP canister vent control valve is damaged or has failed.Fuel tank cap loose, missing or it is the wrong part number.Fuel tank temperature sensor is damaged or has failed.Fuel tank vacuum relief valve is damaged or has failed.Large leak in the EVAP canister or in the fuel tank area.ORVR system is damaged or has a large leak in a component.Refueling control valve is damaged or has failed.Vacuum hose leaking between intake manifold and Purge valve.Here are the codes,take part back and get refund.
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See Figure 1
Fig. Fig. 1: Cross-section of the vapor canister
Fuel Tank Pressure Control Valve
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OPERATION Changes in atmospheric temperature cause fuel tanks to breathe, that is, the air within the tank expands and contracts with outside temperature changes. If an unsealed system was used, when the temperature rises, air would escape through the tank vent tube or the vent in the tank cap. The air which escapes contains gasoline vapors.
The Evaporative Emission Control System provides a sealed fuel system with the capability to store and condense fuel vapors. When the fuel evaporates in the fuel tank, the vapor passes through the EVAP emission valve, through vent hoses or tubes to a carbon filled evaporative canister. When the engine is operating the vapors are drawn into the intake manifold and burned during combustion..
A sealed, maintenance free evaporative canister is used. The canister is filled with granules of an activated carbon mixture. Fuel vapors entering the canister are absorbed by the charcoal granules. A vent cap is located on the top of the canister to provide fresh air to the canister when it is being purged. The vent cap opens to provide fresh air into the canister, which circulates through the charcoal, releasing trapped vapors and carrying them to the engine to be burned.
Fuel tank pressure vents fuel vapors into the canister. They are held in the canister until they can be drawn into the intake manifold. The canister purge valve allows the canister to be purged at a pre-determined time and engine operating conditions.
Vacuum to the canister is controlled by the canister purge valve. The valve is operated by the PCM. The PCM regulates the valve by switching the ground circuit on and off based on engine operating conditions. When energized, the valve prevents vacuum from reaching the canister. When not energized the valve allows vacuum to purge the vapors from the canister.
During warm up and for a specified time after hot starts, the PCM energizes (grounds) the valve preventing vacuum from reaching the canister. When the engine temperature reaches the operating level of about 120°F (49°C), the PCM removes the ground from the valve allowing vacuum to flow through the canister and purges vapors through the throttle body. During certain idle conditions, the purge valve may be grounded to control fuel mixture calibrations.
The fuel tank is sealed with a pressure-vacuum relief filler cap. The relief valve in the cap is a safety feature, preventing excessive pressure or vacuum in the fuel tank. If the cap is malfunctioning, and needs to be replaced, ensure that the replacement is the identical cap to ensure correct system operation.
OBD-II EVAP System Monitor
Some of the models covered in this guide have added system components due to the EVAP system monitor incorporated in the OBD-II engine control system. A pressure sensor is mounted on the fuel tank which measures pressure inside the tank, and a purge flow sensor measures the flow of the gases from the canister into the engine. The purge valve is now called the Vapor Management Valve (VMV). It performs the same functions as the purge valve, however it looks slightly different. A canister vent solenoid is mounted on the canister, taking the place of the vent cap, providing a source of fresh air to the canister.
The PCM can store trouble codes for EVAP system performance, a list of the codes is provided later in this information. Normal testing procedure can be used, see EVAP System Component Testing in this Section.
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