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Thread: Rich Misfire Issues at Cruise

  1. #1
    turbo addict
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    Rich Misfire Issues at Cruise

    Having an issue at cruise in vacuum where the AFR's will oscilate between 10.0:1 to 14.8:1. Vehicle will misfire/stumble and go completely rich on the wideband. It only does this in vacuum and runs great as soon as it hits anything above 0PSI. Its really annoying driving long distances having to constantly play with the throttle to keep the vehicle from going full rich and misfiring.

    I have tried leaning out the part throttle fuel tables and also the base fueling from 22" of vacuum all the way to about 2 PSI, but that didnt do much.

    Vehicle is an 87GLHS, 87T2 electronics, running the 2.5L_MTX_Custom_v13 turbonator cal.

    There are no codes being thrown.

    Could this be a timing issue?

    Any ideas on where to start looking?

  2. #2
    turbo addict
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    Re: Rich Misfire Issues at Cruise

    Anyone?

  3. #3
    Hybrid booster
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    Re: Rich Misfire Issues at Cruise

    How old is your oxygen sensor? When the O2 sends low voltage, the ECU sees a lean mixture. If your O2 sensor is tired, it will send lots of low voltages. The ECU will then richen the mix to get the volts back up. If your WB is an Innovate, it has a simulated NB output you could send to the ECU. Save you the price of a new NB.

    Mike

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    Buy my stuff!!!!!!!!!!! :O) Turbo Mopar Vendor turbovanmanČ's Avatar
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    Re: Rich Misfire Issues at Cruise

    Is that one of Rob's new templates or older ones? He's fixed alot of issues in the new versions.
    1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS! 12.57@104 :O)
    1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
    2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
    2004 GSW TDI, 5 speed, fully loaded, modified.

    Aurora ignition wires for sale. Link to info

    Super60 roller cams or custom/billet cams. Link to info

  5. #5
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    Re: Rich Misfire Issues at Cruise

    From my understanding, rich misfires occur at around 8:1 give or take a point or 2

    However, an ignition fault can show rich on an oxygen sensor as there is unburnt fuel and air (oxygen) being passed straight through the engine. I would look into ignition related problems first. Plugs, gap, wires, coil, base timing, cap and rotor condition, correct wire engagement into the cap, ect.

  6. #6
    Hybrid booster
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    Re: Rich Misfire Issues at Cruise

    Just a minor correction, misfires register as LEAN, as the sensor ONLY SEES THE OXYGEN, not the fuel. If the oxygen isn't consumed in combustion, it gets exposed to the sensor.

    Mike

  7. #7
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    Re: Rich Misfire Issues at Cruise

    Quote Originally Posted by mpgmike View Post
    Just a minor correction, misfires register as LEAN, as the sensor ONLY SEES THE OXYGEN, not the fuel. If the oxygen isn't consumed in combustion, it gets exposed to the sensor.

    Mike
    Thats what I assumed. When the wideband drops down to 9.8-10:1 is when the car will stumble/miss. My wideband is an innovate, so I'll definitely try sending the simulated signal in order to rule out the oxygen sensor.

  8. #8
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    Re: Rich Misfire Issues at Cruise

    Quote Originally Posted by mpgmike View Post
    Just a minor correction, misfires register as LEAN, as the sensor ONLY SEES THE OXYGEN, not the fuel. If the oxygen isn't consumed in combustion, it gets exposed to the sensor.

    Mike
    Dammit, I know that too! Glad you caught that.

  9. #9
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    Re: Rich Misfire Issues at Cruise

    Ran the simulated narrowband signal to the ecu.. Vehicle is still doing the same thing, so it wasn't the stock O2... Any other suggestions

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