Control Plunger Retaining Ring | FerrariChat

Control Plunger Retaining Ring

Discussion in 'Technical Q&A' started by 85cab, Aug 23, 2020.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. 85cab

    85cab Rookie

    Jun 30, 2015
    40
    Ottawa, Canada
    I've been reading a lot of threads that discuss the K-Jetronic fuel distributor, its function and repair. However, I've yet to come across anything that specifically addresses the control plunger retaining ring. It seems that some fuel distributors have this ring, but many don't.

    In discussions about FD removal, the main caution is "don't let the plunger fall out during FD removal from the air flow base". My FD (for my '85 Mondial QV Cab. Euro version) has a retaining ring, so there is no chance that the plunger can be removed until that ring is first removed.

    My question is: Is the sole purpose of that retaining ring to stop the plunger from falling out, or does it also have a secondary function?
    Which leads to my second question: is there a specific height at which the retaining ring should prevent the plunger from downward movement?

    My thinking is that if the retaining ring forks are bent too far toward the FD body, the plunger would rest high in the FD body and would allow for fuel to pass through to the injectors, even if the fuel pump was running but the engine was off (fuel system pressure check scenario).

    I've attached a couple of pictures which I hope will clarify my questions. In these pics the control plunger was stuck, but has since been fixed.

    Any insight would be very much appreciated! Thanks.

    Image Unavailable, Please Login Image Unavailable, Please Login
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,932
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    My comment would be that that "wrap-around" plunger travel limit stop sure looks like a clever "fix" implemented after the initial design.-- the cross-section drawings of the K-Jet fuel distributor in both the Mondial 8/QV WSM and TR WSM do not show that part looking like that.
     
  3. 85cab

    85cab Rookie

    Jun 30, 2015
    40
    Ottawa, Canada
    Yes, I tend to agree that this was unlikely part of the original design. The images in the QV WSM and even in the Bosch K-Jetronic Technical Instruction contain no reference to this ring.
     

Share This Page