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info on QV air injection.

Discussion in '308/328' started by rockford, Aug 13, 2012.

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  1. rockford

    rockford Karting

    Jan 23, 2009
    54
    houston, tx
    Full Name:
    rockford woods
    #1 rockford, Aug 13, 2012
    I am in process of repairing this system on my 85. The small cheap plastic vacuum operated air shutoff valve is pretty much destroyed and has been for a while. The diaphragm is shot and so it was always open. The tee which split the hose behind this valve has a nice hole it it as well which resulted in the engine being filthy. I have sourced a Mercedes replacement in real honest to goodness actual metal for the ridiculously priced plastic POS. Ditto for the tee.

    I do not understand why this system is called pulse injection. Does anyone here have a description of how it is supposed to function? All there seems to be is a simple vacuum operated diaphragm to hold the valve open above a certain vacuum level. It would also seem that lower pressure in the exhaust end would cause additional air to be drawn from the front of the air box since this valve is directional.

    I know most of you have probably removed this crap from your cars along with the air injectors but I believe after reading the laws here in Texas that it is not legal to remove it. It does not have to work but is supposed to stay on the car.
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,839
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Aug 13, 2012
    Last edited: Aug 13, 2012
    There's a decent description of the system in your 307/84 OM on pages 73-75, and some good figures showing the components.

    When really "cold" (i.e., water thermoswitch closed and oil thermoswitch closed), the electrovalve is not energized. This prevents vacuum from reaching the cut-off valve keeping it closed (so no extra air enters the exhaust stream). The injection system runs in open-loop mode and ignores the O2 sensor signal.

    When "cold" (i.e., water thermoswitch closed and oil thermoswitch open), the electrovalve is energized which applies vacuum to the cut-off valve, which opens it, and allows the exhaust "pulses" to draw in extra fresh air. The injection system runs in open-loop mode and ignores the O2 sensor signal.

    When "warm" (i.e., water thermoswitch open and oil thermoswitch open), the electrovalve is not enegized. This prevents vacuum from reaching the cut-off valve keeping it closed (so no extra air enters the exhaust stream -- which is important in this mode because this would "fool" the O2 sensor). The injection system runs in closed-loop mode and uses the O2 sensor signal to alter the FV signal duty cycle in order to alter the A/F ratio.
     

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