Why do things always snowball or more FI Problems ...

Discussion in 'Technical Q&A' started by alfa-guy, Nov 18, 2004.

  1. alfa-guy

    alfa-guy Rookie

    Jan 27, 2004
    Ok, so I'm woring on my QV which has not been running properly and thought I pretty much had it figured out.

    Then the frequency valve lost power along with a few other things. Turns out that the fusible link inside the Oxygen Sensor Protection Relay (at least that is what is called in the wiring diagram) popped.

    I soldered a jumper into the relay, and installed an external 3 amp fuse temporarily. Initially I thought maybe I shorted something out in poking around with the DMM.

    No such luck, turns out that whenever the throttle is closed (as in during decleration) the fuse pops.

    This is a result of the signal coming from the differential pressure switch. In checking the wiring to and fro, I discovered that the throttle switch is dead.

    Fortunately the throttle switch is the same as is used on some BMW's and other cars so I was able to find one pretty reasonably, unfortunately it is on the other side of the country so will be a week or so before it is here.

    Whether the throttle switch is the initial cause of the fusible link popping, or the poor idle (which was the initial problem ... thought it was the WUR as the control pressure seems too high) I won't know until I get the replacement throttle switch and put it all back together.

    If anyone knows more about the interaction of all these components and their wiring I'm all ears.

    There's something like 4 (or more) relays that are all interconnected tying all these systems together. I'm tearing my hair out trying to follow the logic of what controls what.


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  3. KurtK328

    KurtK328 Formula Junior

    Mar 6, 2001
    Villeneuve-Loubet, France
    Full Name:
    Kurt Kjelgaard
    Wouldn't you need a 10 amp fuse instead of 3?
  4. alfa-guy

    alfa-guy Rookie

    Jan 27, 2004
    Good Question ... I don't know what the rating is/was of the fusible link inside the relay, simply assumed it was pretty small.

    Also measured about 1.5 amps through the circuit with the everything working.

    However, I was looking at the wiring diagram of the 328 last night (remember I'm working on a 308 QV) and it appears that on the 328 they took the fusible link out of the relay and replaced it with an external 10 amp fuse.

    So you may very well be right ...

    Still, makes me wonder why the fusible link popped in the first place?


  5. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    Hi Jeff,

    Going through fault-diagnosis right now on my 328. In the service manual, there is a procedure for systematically checking the Jetronic ECU inputs/outputs - is there something similar for 308 QVs?

    Shoot me and email & I'll send you the beta-version of my write-up. I'm seeing some odd voltages though.

    :) Carl

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