512TR: Puzzling fuel pump behavior | FerrariChat

512TR: Puzzling fuel pump behavior

Discussion in 'Boxers/TR/M' started by awatkins, Jun 27, 2019.

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  1. awatkins

    awatkins Formula Junior

    Apr 10, 2005
    396
    SFO Peninsula
    Full Name:
    Alan Watkins
    #1 awatkins, Jun 27, 2019
    Earlier today I unseated each of the connectors around the fuse/relay panel in order to check for signs of corrosion, slack terminals, overheating, etc. After I carefully reseated each connector and fired the car up, it rewarded my attention by operating one of its fuel pumps on and off at about 1 cycle/second; I can hear and feel relay R operating in this way. Prior to this the car ran fine.

    I've been staring at the WSM diagrams trying to imagine what related failure might cause the behavior, but have not enough experience debugging EFI systems to come up with a theory and don't know what control logic lies behind the fuel pumps. So before I go into full blown diagnosis mode, I wanted to ask if any of you EFI-experienced guys might have any hints, suggestions or theories.

    Thanks in advance.
     
  2. xplodee

    xplodee Formula 3

    Jan 3, 2017
    1,101
    Allentown, PA
    Full Name:
    Tim
    #2 xplodee, Jun 28, 2019
    Could it just be a bad relay?
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,123
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #3 Steve Magnusson, Jun 28, 2019
    Certainly try swapping relay R and relay T as xplodee suggests to see if the problem moves to the 7-12 bank.

    If the problem moves = get a new relay.

    If the problem stays on the 1-6 bank = try to determine if relay Q is also "winking" on-off with relay R. The logic is:

    relay Q supplies the +12V power to run the 1-6 Motronic ECU which then runs relay R

    (and likewise, relay U supplies the +12V power to run the 7-12 Motronic ECU which then runs relay T)

    If relay Q is also winking = try swapping relay Q and relay U to see if the problem moves.

    If relay Q stay "on" steady, but relay R (and relay T when moved to the relay R position) winks on-off = swap Motronic ECUs:

    If the problem moves to the 7-12 bank = bad sign for the Motronoic ECU (now moved to the 7-12 bank)

    If the problem stays on the 1-6 bank = I quit! ;)

    Try some of that and give a shout back with what you find...
     
    Shamile and turbo-joe like this.
  4. awatkins

    awatkins Formula Junior

    Apr 10, 2005
    396
    SFO Peninsula
    Full Name:
    Alan Watkins
    #4 awatkins, Jun 29, 2019
    Long story short, the problem followed one of the ECUs. (Oddly in the new position the tach doesn't bounce as much nor is the variation in engine pitch as large) but it's definitely still there and I can hear and feel it in the corresponding FP relay. Swapping the U/Q ECU relays and R/T FP relays had no effect. BTW I reported the initial symptom wrong: it was detectable on relay T, and with ECUs swapped is now detectable on relay R. So the suspect is the ECU driving cyl.. 1-6.
     

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