Is it the oxygen sensor?

Discussion in 'General Motoring' started by Bill ing, Jul 22, 2004.

  1. Bill ing

    Bill ing Guest

    Needing a coroboration of opinions here...

    200,000km/120,000Mi. on a 97 SL1 which has had amazingly little trouble.

    But the "Service Engine Soon" light is now lit steadily and I haven't driven
    it through a puddle and it's the same low grade gas I've been using for the
    last few years.

    The plugs were changed 15,000Km ago when it started to sputter going up
    minor hills and PCV valve too was changed then. Wires are the same
    Mangacore ones that I put in at 100,000Km ago.

    Starts have been funny over the last few months in that it doesn't necearily
    start on the first turn and I could hold the key there for a while and get
    nothing, but if I let go and try it again, it starts immediately.

    Also, if it did start after holding it for a while, the start is kinda rough
    and sputtery.

    From my RC airplane days, that was always a sign of too rich a mixture.
    Hence I'm guessing O2 sensor.

    Also, anyone know a rough estimate on cost for one of these things?

    Bill ing, Jul 22, 2004
  2. Bill ing

    Blah Blah Guest

    Get the code read. Low grade as in octane? Makes no diff, 87 octane is
    all you need for your engines compression ratio.
    If you dont check your wires with an OHM Meter then you never know what
    you got. Look your plugs over again as well.
    Check out fuel pressure. Whens the last time you changed your fuel
    filter? The fuel pump runs for 2 seconds after the key is turned to run.
    You might be waiting for fuel pressure to make it past your fuel filter.
    25,000 miles Should be everyones limit on fuel filters. If you starve
    electric fuel pumps of fuel or restrict the flow of fuel you will no
    doubt damage electric fuel pumps.
    O2 sensors dont usually go bad on their own but a bad running engine
    will take them out.
    Fuel filter 15 bucks US.
    Fuel Pump 200-400 bucks US.
    Filling up before your tank goes below 1 quarter, Priceless.
    Blah Blah, Jul 22, 2004
  3. Bill ing

    C. E. White Guest

    The O2 sensor has no impact on the start-up. In fact, the
    computer doesn't even use its output until the engine is
    warmed up. The start problems sounds more like a fuel
    pressure problem. When you turn the key, the fuel pump only
    runs for a very breif period unless the engine starts. If
    the pump is weak, or the the system isn't holding pressure
    when the engine is turned off, then there might not be
    sufficient fuel available to start the engine during the
    breif period of fuel pump operation during the start
    sequence. Going through the starrt sequence a second (or
    third or fourth) time gives you another shot of fuel. Since
    you got one shot of fuel from the first start attempt, the
    second (or further) attempts can provide enough fuel to
    start the car. Another fuel system problem that can cause
    start problems is a leaky injector. These can hurt in two
    ways -1), a leaky injector(s) allow the fuel system
    pressure to bleed off, causing the problem discussed above,
    usually after a long period of the car setting, and 2) they
    can casue one cylinder to be flooded out - usually after a
    shorther period of setting and followed with a black cloud
    of smoke when the car actually starts.

    I suggest that you need to have your fuel pressure checked.
    If the pump is going bad, you can have insufficient
    pressure, leading to hard starting, and a lean mixture.


    Ed White
    C. E. White, Jul 22, 2004
  4. It's either a fuel pronblem (see other p;osts), or maybe a flakey
    ignition module (I've had this on other cars). It's NOT the O2 sensor.
    The O2 sensor doesn't do anything until the car's warmed up, the
    computer's decided it's waited long enough, the signal's in range, and
    your foot's on the gas.
    Philip Nasadowski, Jul 22, 2004
  5. Bill ing

    Lane Guest

    Hence I'm guessing O2 sensor.

    Don't guess. Spring for a diagnostic from the dealer and it will pay for
    itself if it prevents you from buying one part you don't need.

    Lane [ l a n e @ p a i r . c o m ]
    Lane, Jul 22, 2004
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