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Thread: 3400 LA1 EVAP purge switch conditions

  1. #1

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    3400 LA1 EVAP purge switch conditions

    Should the vaccum be noticeable in line between EVAP Purge vacuum switch and EVAP Canister when engine on idle,warm.
    Which conditions command Purge Valve and Vaccum Switch to operate(open) ?
    Zebe9
    Pontiac TS \'96 3400
    -----------------------
    my way or highway

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  3. #2
    Iron Head Enthusiast geoffinbc's Avatar
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    Yes there will be vacuum. With a warm engine only. Should not be any when cold.
    1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
    1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
    Because... I am, CANADIAN

  4. #3

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    EVAP vacuum

    UUUuuuuuuuuuhhh !! And theres NO vaccum there !
    And: EVAP vaccum switch mounted on rear rocker arm cover is hardly visible ,nearly inaccesible(maybe from underneath)-wheres Purge valve next to it(?!), how the hoses should be properly connected starting from purge canister to purge valve via EVAP switch ?
    No DTC indicating EVAP failure so far.
    Could it influence fuel consumption anyhow ?
    Zebe9
    Pontiac TS \'96 3400
    -----------------------
    my way or highway

  5. #4
    Iron Head Enthusiast geoffinbc's Avatar
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    I am not familiar with the 3400 EVAP systems. I cannot tell you how the hoses should be connected. A failure of the system should not really affect fuel consumption. At least in theory.
    1993 EXT. CAB, 3.4L V6 TBI, 5spd manual. Sonoma
    1990 4Door, 3.2L V6 TBI, 5spd manual. 4X4. Trooper
    Because... I am, CANADIAN

  6. #5
    Quote Originally Posted by gm
    The EVAP purge solenoid valve allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the EVAP purge solenoid valve (purge On). The EVAP purge solenoid control is Pulse Width Modulated (PWM) or turned On and Off several times a second. The PCM controlled PWM output is commanded when the appropriate conditions have been met:

    Engine coolant temperature above 25C (77F).
    After the engine has been running about 2 1/2 minutes on a cold start or 30 seconds on a warm start.
    The vehicle is operating in closed loop fuel control.
    Canister purge PWM duty cycle varies according to operating conditions determined by mass air flow, fuel trim, and. intake air temperature. Canister purge will be disabled if TP angle increases to above 70%. Canister purge will be re-enabled when TP angle decreases below 66%.

    The EVAP purge vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge solenoid. The EVAP Vacuum Switch will open when vacuum increases to greater than 5 inches of water in the purge line. The EVAP Vacuum Switch is used by the PCM to monitor EVAP Purge solenoid operation and purge system integrity. The EVAP Vacuum Switch should be closed to ground with no vacuum present (0% EVAP Purge PWM). With EVAP Purge PWM at 25% or greater, the EVAP Vacuum Switch should open.
    Colin
    92 Sunbird GT, 3200 Hybrid 13.99@ 95.22 (2004)
    90 Eagle Talon TSi AWD 10.54 @ 129mph.

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