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Thread: Never ending smog issues -- high hydrocarbons

  1. #1

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    Never ending smog issues -- high hydrocarbons

    After adjusting the timing on my 1988 Mitsubishi Mighty Max (engine swap to a 1991 or 1992), and readjusting the Idle Speed Control Servo to lower the idle speed, I thought I was all good to go with smog.

    However, at the appointment today the referee stated that the hydrocarbons are too high.
    Acceptable max is 130, my truck is reading 233.

    Any thoughts on how to lower the hydrocarbons? There are no vacuum leaks... I was thinking adjusting the throttle position sensor?

    Can anyone explain how to adjust the sensor and what the resistance values are? or where I can look them up?

    Also, there seems to be a slight misfire that I cannot locate so far...any ideas?

  2. #2



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    I new cat is going to clean it up. After 26 years it's probably due.
    You just want to make sure it's as close to the engine as possible. High HC is an engine problem. Things like the EGR not working, valve adjustments, low compression, bad coil, things like that.
    High CO is the carb.
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  3. #3

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    Quote Originally Posted by Mightymax View Post
    Can anyone explain how to adjust the [TPS] sensor and what the resistance values are? or where I can look them up?

    Also, there seems to be a slight misfire that I cannot locate so far...any ideas?
    The Haynes book has the specifications for the TPS resistance value...I think it's .5 but don't hold me to that. There is a section on the forum that you should be able to find the specs.

    I followed the book's steps, and first pulled the code from the connector at the fuse box, which told me the TPS was bad. Before that, I tried adjusting and adjusting and had similar problems to what you describe. I went so far as to hook up to the ECU as instructed only to find it was off the charts.

    Loosening the two adjusting screws, try simply setting the TPS to its lowest setting, which would be clockwise until it stops, then move it back 1/16"...see if this affects anything. I replaced the TPS (expensive, yes) and it solved many poblems. Once idle is where it belongs, timing can be adjusted much more accurately, and the TPS does help with the idle. The new TPS solved sputtering at warm up.

    Here is a crude illustration of the TPS and settings

    X + < > - X the X's being the screws, left arrow = counter-clockwise.

    The voltmeter is plugged into the ECU for readings/adjustments. You really need a book to have on hand if you keep your truck: it's just good sense.

    Much luck, hope this is of some help.


    Roy

  4. #4



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    The reading on the TPS is .5 Volts with throttle plate closed, 4.5 to 5 volts WOT on the DC scale. if you are off on either end, use the adjusting screws for the throttle plate first before playing with the tps sensor, unless you just installed it.
    Pennyman1
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    Living the D-50 lifestyle since 1980

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