EVAP Effect on Emissions and Driveability

During Two Speed Idle tests, it is not uncommon for vehicles to fail off idle tailpipe tests for excessive CO emissions due to normal evaporative purge cycle operation. It is also possible for the charcoal canister to become saturated with liquid fuel to the degree that it becomes unserviceable.

To avoid emissions failures due to normal evaporative emissions purge cycle, the vehicle should not be tested after long hot soak periods, prolonged idle or after having been left in sitting in the sun on a hot day. All of these conditions will cause large amounts of fuel vapor to store in the charcoal canister. To put the EVAP system through it's normal purge cycle, the vehicle can be driven at highway speeds for five minutes. This should purge any vapor from the canister which would normally accumulate during the above mentioned conditions.

If the canister continues to cause high CO emissions after a normal purge cycle has been performed, it is possible that the canister is irrecoverably saturated. If the EVAP is suspected as potential cause of high CO emissions failure or rich driveability problems, the following checks should be made:

• Isolate the EVAP system from the engine intake by removing the purge port hose from throttle body port.

• Test vehicle with EVAP system isolated.

If the EVAP system is determined to be at fault, use procedures in the appropriate Repair Manual to inspect the charcoal canister, filter, check valves, TVV or VSV and the related vacuum plumbing.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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  • joonas
    Can evap canister have effect on drivability?
    4 years ago
  • jessika
    Can evap vsv affect engine idle?
    3 years ago
  • jussi
    Can purge canister affect drivabiliry?
    2 years ago

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