Do I need to replace my intake manifold?

Discussion in 'General Motoring' started by Raul, Oct 23, 2007.

  1. Raul

    Raul Guest

    My 94 Civic has the check engine light on. Mechanic says its the O2
    sensor, which sounds reasonable. However, he says that the sensor is
    essentially melted onto the intake manifold, so that the IM needs to
    be replaced too. Does this make any sense? The IM replacement is way
    more expensive.

    Raul, Oct 23, 2007
  2. Raul

    Elle Guest

    You should be able to get the code read at an Autozone at no

    The code may indicate a problem with the O2 sensor, but this
    does not mean it must be replaced. Are their symptoms of
    rough running when the car is driven?

    Your car certainly is old enough that the O2 sensor may be
    The O2 sensor is mounted on the exhaust manifold. It
    monitors the oxygen content of /exhaust/ gases and sends a
    signal to the engine control system to maximize engine (fuel
    burning) efficiency and minimize pollution.

    Has your mechanic actually put a wrench to the sensor and
    tried to remove it?

    If it seems the sensor has failed, and if you are the least
    bit handy, I would take off the exhaust manifold shield (and
    maybe any other small interference of parts), soak the O2
    sensor's threads as best I could with the penetrating oil
    "PB Blaster" (around $5 a can at Autozone and Wal-Mart).
    Then I'd borrow an O2 sensor wrench from Autozone (no
    charge) and try to remove it. If you can remove it, you can
    buy an OEM sensor online and replace it yourself.

    Here's a drawing of the O2 sensor location:

    Great and inexpensive OEM O2 sensors:

    For most 1994 Civics, the sensor costs about $70 at this
    Elle, Oct 23, 2007
  3. Raul

    Tegger Guest

    As Elle says, the sensor is in the EXHAUST manifold.

    Mechanic should reset the Check Engine light and simply wait to see if it
    comes on again. Often the problem will not recur.

    It is important that you specify the actual numeric code that was

    Even if the sensor does actually need to be replaced and is seized in the
    manifold, you can still just wind it out of the hole, then re-cut the
    threads in the manifold with a spark plug tap. A lot easier and cheaper
    than a new exhaust manifold!
    Tegger, Oct 23, 2007
  4. Raul

    motsco_ Guest


    Your diagrams are at You want to look at the
    exhaust manifold. prices are there too.

    motsco_, Oct 23, 2007
  5. Raul

    Matt Ion Guest

    Just to add to what Tegger and Elle have already said... it sounds like
    either you misunderstood your "mechanic", or he's simply an idiot.

    I'd get a second opinion before proceeding.
    Matt Ion, Oct 24, 2007
  6. Raul

    z Guest

    Going just by the numbers, the sensor is probably thoroughly stuck in
    the exhaust manifold, and either the mechanic or the OP misspoke. On
    the other hand, if the sensor really is melted into the intake
    manifold, he definitely needs some serious repairs.
    z, Oct 24, 2007
  7. Raul

    z Guest

    Like everybody said, it's probably stuck into the exhaust manifold,
    and it's probably more feasible to remove it with penetrating oil,
    heat, and brute force than replace the manifold. Because if it's
    stuck, then i can guarantee you that the mounting studs and nuts for
    the manifold to the head and the catalytic converter are going to be
    equally stuck, and there are more of them than just the one sensor,
    and it's less feasible to just destroy them to get them out and
    replace them than it is with the sensor.
    z, Oct 24, 2007
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