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DIY: Eliminate CEL for a Knock Sensor

Discussion in 'Engine Tech / Drivetrain DIY How-To's' started by obracer12, Dec 19, 2012.

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  1. obracer12

    obracer12 New Member Registered VIP 5+ Year Member

    May 8, 2008
    assuming you have a CEL on for a knock sensor for reasons you may not know or in my case and engine without a knock sensor using an ECU with one equipped( did not get the tuning software capable of eliminating it, slight oversight in my budget-build planning for a turbo/swapped DD), here is what you do.

    1) Go to radio shack and pick up a Piezo Transducer Part number #273-073 ( kept with the speaker equipment ) I got mine for $2.15 out the door.

    2) locate your OBD pin associated with your knock sensor ( in my case OBD1 pin D3 would be the one)

    3) Remove ECU fuse and let sit for about 5-10 minutes.

    4) remove plug from ECU and remove pin set socket from harness. Insert wire into socket receiver , solder and revers steps to re-assemble.

    5) run about 4-5 feet of wire from he ECU into the engine bay.

    6) solder the ECU wire to the "+" side of the transducer.

    7) tricky bit, find a portion of the engine that vibrates to attach the transducer. Since the transducer generates it's own charge ~ .6-1.7 volts ( enough to trigger a good knock response from the ECU) you will need to find a place that vibrates during normal engine operation. I selected the under side of the intake manifold and it worked like a charm. A Zip tie to the Cylinder 2 runner was my means of affixing it there.

    8) find a firm ground connection. Mine was to the starter ground due to it's close proximity.

    9) Solder a length of wire long enough to get to your ground to the "-" side of the transducer.

    10) attach the wire from the - to the ground

    11) re-install the ECU fuse.

    12) Drive - if you still throw a CEL you need to find a better place to attach your transducer.

    This helped a few ways:

    Got rid of the annoying CEL.
    Brought my ECU out of an adjustment loop to a rich condition without resetting the unit every so often.
    - became especially annoying when I was trying to data log and kept creeping into rich A/F even under full boost.
    Helped me pass a B16 turbo in a 93 hatch through state inspection by bringing my HC and CO emission down.
    Smoothed out engine idle overall.

    Hope this helps you guys doing budget builds and if you have any questions feel free to post.


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