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Thread: Erratic AFR - running rich/lean spikes/bogging

  1. #1
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    2002 protege5

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    Erratic AFR - running rich/lean spikes/bogging

    First time poster, fairly recent lurker.
    I have a 2002 protege5 with problems that I can't figure out. The car ran fine for years and all of a sudden I started getting a bogging/hesitation under acceleration. The afr gauge is all over the place; sometimes idling at 16.x and sometimes idling around 14, but not consistently. While cruising my afr is around 13, but jumps back and forth from about 12.x to 17 with sudden drops to 10. Sometimes it will stay at 10 from cruising to stopping and then accelerating. Which makes it almost impossible to take off from a red light. It's causing serious bogging/studdering/hesitation issues to the point where it's almost undriveable.
    I've also recently noticed a rapid clicking noise under hard acceleration coming from the passenger floor board where the ecu is mounted.

    Notes to add that may be suspect:
    The noise of the fuel pump briefly gets less loud when anything electrical is turned on.
    Fuel pressure immediately starts to drop once it's primed with the engine off.

    Mods are:
    440 injectors
    255 walboro
    Split second ftc1
    Forged internals
    TSI turbo kit
    Aem wideband
    Mazdaspeed ecu
    Aeromotive fpr
    Aftermarket fuel rail

    List of things I've done to attempt to fix the issues.
    Changed upstream and downstream O2 sensors
    Cleaned MAFS
    Pressure tested for boost leaks
    Changed wastegate
    Changed spark plugs, coils and wires.
    Changed the fuel pressure regulator.
    Checked compression.

    Any ideas of what the problem could be?
    Last edited by Slowerp5; 02-05-2018 at 08:15 AM. Reason: More details.

  2. #2
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    Inspect or replace your pressure regulator solenoid valve.

    You might want to replace your high pressure fuel filter.. They plug up over time.

    Last edited by pcb; 02-05-2018 at 04:15 AM.
    The Diagram Dude

  3. #3
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    2002 protege5

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    The pressure regulator control valve has been blocked off for years without any issue. Also, would the bad filter cause it to run so rich? I would think a clogged filter would only make it run lean.

  4. #4
    The Diagram Dude pcb's Avatar

    2002 mazda protege 5

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    Quote Originally Posted by Slowerp5 View Post
    The pressure regulator control valve has been blocked off for years without any issue...
    I know very little about mods including turbos. I would have thought you'd throw a code by plugging that valve.


    Quote Originally Posted by Slowerp5 View Post
    ..Also, would the bad filter cause it to run so rich? I would think a clogged filter would only make it run lean.
    Yea,.. That makes sense but replacing your filter is probably a smart idea regardless.

    Quote Originally Posted by Slowerp5 View Post
    Fuel pressure immediately starts to drop once it's primed with the engine off.
    As far as I know there is no fuel check valve (at least in a stock setup) maintaining fuel pressure is a function of the fuel pump itself.
    If your fuel filter is plugged, your fuel pump can be stressed pushing fuel through it and wear out the pump until it stops holding pressure.

    I'm guessing you need a new fuel pump and high pressure fuel filter (aka fuel pump housing).
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