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Couple of questions on coolant temp sensors for a 308 2V Injected

Discussion in '308/328' started by dave80gtsi, Oct 2, 2004.

  1. dave80gtsi

    dave80gtsi Formula 3
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    Nov 3, 2003
    1,473
    Ohio
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    Dave Meredith
    #1 dave80gtsi, Oct 2, 2004
    Greetings to all. I am trying to do some electrical diagnostic work on my USA spec 2V 308 GTSi and have two (2) questions:

    1) I still seem to have that funky 2500 rpm high idle when the engine is stone cold, traceable back to the archaic cold start smog requirements when new. I have heard secondhand that one can defeat this nasty feature easily by either shorting or opening the terminal connections at a temperature sensor, and I believe the sensor in question is the one located on the underside of the coolant expansion tank.

    Can anyone confirm that this is indeed the correct sensor for this task? Should I either short together, or should I open by disconnecting the pair of electrical terminals leading to it? But, more importantly, is this the ONLY function of this temperature sensor - in other words, are there any 'side effects' when one does this operation?

    2) What is the specific function of the coolant temperature sensor which is located on the face of the thermostat housing, directly above the water pump? I do not believe that this is the sending unit for the dashboard water temperature gauge - that one is located on the end of the small manifold in the center of the 'V' valley beneath the intake plenum ( ... correct?). Thus, this mystery thermostat housing temperature sensor appears to be an "extra" one - does anyone know with certainty what job it serves?

    Thanks and Cheers - DM / Ohio
     

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  2. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
    19,897
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    Steve Magnusson
    #2 Steve Magnusson, Oct 2, 2004
    See page 76 in your 216/81 OM -- it talks about how the EGR system uses the engine coolant temperature as a control input (ergo -- coolant temp sensor required).
     
  3. M.James

    M.James F1 Rookie

    Jun 6, 2003
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    Michael.C.James
    #3 M.James, Oct 2, 2004
    That's funny....Dave's trying to disconnect the very Cold-Start 'feature' I'm trying to get working in my car. No, Dave, we're not switching cars....
     
  4. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    300
    #4 carlrose, Oct 3, 2004
    Hi Dave,

    The sensor under the coolant reservoir tank is the temperature sensor for the K-Jetronic FI only; this does not input to the dash gauge. Temp sender for the dash (on my 328) is in the crossover coolant manifold between the two cylinder heads (under the plenum). 328 does not have a sender on the thermostat housing; this may be analagous location for 308 model.

    The FI temp sender, as I recall, reads continuity until the coolant warms to pre-set temperature then "opens" to infinite resistance. You can check this by allowing car to warm up then disconnecting either one (or both) input wires (effectively causing infinite resistance). If no change in engine speed, this is "warm/hot" endpoint. Bridging with paperclip will revert to "cold" and correspondingly increase your idle speed. Or if you prefer could always pull out the multimeter and take readings. Interestingly, this part is ferrari-specific (not Bosch) but fortunately not expensive. I purchased one from Algar for about $25 earlier this year.

    If you wanted to bypass this function I suppose you could externally bridge terminals or connect an inconspicuous jumper between terminals when installed. Not certain if this would affect CSI though (think this is limited to TTS control & not ECU).

    :) Carl
     

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