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348 Throttle Microswitch(es)

Discussion in 'Technical Q&A' started by MarkCollins, Mar 23, 2004.

  1. MarkCollins

    MarkCollins F1 Rookie
    Owner

    Jul 2, 2002
    3,199
    South England
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    Mark Collins
    How important are these?

    To explain I have a 348 engine in my project which is a later engine with twin microswitches and the loom has two connectors but the ECU's are from an earlier model, Motronic 2.5 I believe which only used one on bank 5 - 8.

    If I connect both of them up and rev the engine to 3 to 4k the engine nearly always dies unless you repeatedly pump the throttle then it recovers but in the meantime bank 5 - 8 has shutdown, removing and reconnecting the throttle switch on 5 - 8 whilst engine running makes them work again, the same happens if I connect just one on either bank but if I leave both disconnected the engine runs fine, doesn't stall, no banks cut etc.

    I'm sure it's becuase of the mismatch in loom/ ECU and can rewire it but do I need to? The manual suggests they help the ECU's to ensure idle but that works anyway

    btw the Engine has no cats, thermocouplers, Lambda probes etc

    thanks for any advice
     
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  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    20,454
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    Steve Magnusson
    Usually the idle microswitch is used to tell the injection ECU to dummy-up a little when operating closed-loop at idle and not try to run in such a super-tight closed-loop A/F optimizing fashion (which can cause RPM wander at idle). Since you've removed the Lambda (O2) sensors (i.e., your system has no way to operate closed-loop) I'm surprised that they have any effect at all -- although, as you said, the looms may be different so might be causing some other wiring problem.

    Have you checked the OMs of F using each of the two Motronic systems that you're trying to marry (www.owners.ferrari.com)? There might be a fairly decent injection system schematic given for each so you could possibly compare those -- just a thought...
     
  4. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,662
    Without th4e oxygen sensors, the computer is in the dark about how much or how little fuel to give the engine. The ECU has an algorythm to search for a near idel fuel mixture, without the oxygen sensor, it searches in vain ending up either too lean or too rich as it receives no signal to tell it when the fuel mix is correct.
     
  5. MarkCollins

    MarkCollins F1 Rookie
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    Jul 2, 2002
    3,199
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    Mark Collins
    Mitch

    The earlier (Euro) 348 engines had no sensors (Oxygen or otherwise) and didn't have cats, reading the workshop manual suggests the mixture is determined by measurement from the airflow sensors

    I'm more than ready to be corrected though as my knowledge in these areas is weak at best!! :)
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    20,454
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    Steve Magnusson
    The "main" mixture control is via the airflow sensing device, but there will be another gizmo (or gizmo section) that add or subtracts small amounts of fuel from the "main" amount (when the output from an O2 sensor is available to run closed-loop). During cold-running, or when an O2 signal is not available (like on the non-US sans Lambda versions), the gizmo is probably designed to default to adding some fixed mid-level amount of fuel (that might vary somewhat with coolant temperature).

    Do you know if the sans Lambda 348 versions have an idle microswitch involved in their control system? (Still might if it's also used as a WOT microswitch, but would be a big clue if it missing from the sans Lambda version IMO.)
     
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  8. MarkCollins

    MarkCollins F1 Rookie
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    Jul 2, 2002
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    Steve

    According to the info I have (Workshop Manual) the sans Lambda had one Microswitch (on banks 5 - 8) which fed both ECU's but it only has 3 positions, shut, middle and open
     
  9. fatbillybob

    fatbillybob Two Time F1 World Champ
    Consultant Owner

    Aug 10, 2002
    20,548
    socal
    2.7 motronic loom is not compatible with 2.5 motronic ecu's. Do one or the other. You either need the 2.5 looms or the 2.7 ecu's. I have an extra set of late model spyder 2.7 ecus if you need. They make the most power. The 2.5 is lacking hence the 2.7. It was a big difference. Set-up is totally different forexample the 2.5 uses one tps and 2.7 needs 2 tps.
     

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