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  1. #1

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    01' SC2, power loss on open loop, hard bucking at light throttle.

    Hey guys. Googling on and off for six months but as of two days ago it's time to ask for help.
    Car is an 01' SC2 Manual, California emissions, 263,XXX miles. Gas mileage is optimal, no current CEL.

    Previous symptoms: CEL for P0301 (vac line behind manifold) / P0341 (replaced 1/4 coil)
    CEL for Upstream o2 (Denso, app specific)
    Idle hunting
    Throttle stuck during January (2.7K~, felt like a cruise control icing, snapped throttle closed with pedal, fixed immediately)
    Hard start when warm, fixed by letting the car prime for 3~ seconds in on position. IF cold, car starts immediately.
    Runs fine honestly, I drove it ~15k like this.

    Now here's the one that's been bugging me. The car loses all of it's power once it reaches operating temp and goes into closed loop.
    Verified by going over ~80% throttle and as soon as the car kicks back into WOT mode it's got it's power back. It is not gradual, it is most definitely
    closed / open loop issue.
    My CEL has been off for months now, it does work. Ran codes the other day and got a cam sensor code, thought "huh maybe the coil is out again", replaced it.
    As of replacing the coil, the car bucks HARD as soon as you crack the throttle. Falls completely on it's face and will bog out and kill if you don't give it more gas and put the clutch a hair back in.
    30%+ Throttle is fine, no bucking, no issues at steady throttle. Light throttle changes feel like they're shutting the engine off.
    Ran datastream on a current Snap-On HD Truck tablet with an OBD adapter and all sensors are good voltages(I think?). Fuel trims, timing, o2 readings, everything looks good. Map is responsive with no flat spots,
    TPS is good 0-100% with no drop-offs. Scan tool is for medium duty and up trucks so I doubt it's smoothing the data.
    Reading no misfires, no codes, no CEL or freeze data.

    This might be a dumb question but can a bad coil cause harsh bucking ONLY when you first touch the throttle, and provide good
    spark moving through RPM's and at other amounts of throttle?
    Holding the pedal steady will allow the engine to "catch up" after about a half-second and it's fine until you move your toes 1/8''.
    Will our ECM give false datastream?

    Any suggestions? I have a multimeter.

  2. #2

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    Check for a clogged cat. Disconnect exhaust and see if there is any change. P.s. if you have an exhaust mani with a cat it might be there.

    Sent from my LG-H700 using Tapatalk

  3. #3

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    Can cats cause even power loss at all RPM only when the car warms up and unclog completely as the throttle tips from 79 to 80%?
    I'm half snarky but half curious.
    Pulled 02 sensor from Mani and car did not run better. Good flow from tail, no sulphur smell or glowing pre-cat.

  4. #4
    Resident Electromotive Expert importsdontlikeme's Avatar
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    01' SC2, power loss on open loop, hard bucking at light throttle.

    ICM maybe?


    Sent from my iPhone using Tapatalk Pro

    Interested in a solid engine management system? Ask me about Electromotive engine management.

  5. #5
    6S Moderator S.Bretz's Avatar
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    The coil pack tower ends need to be clean. If you had one corroding and are still using those wires then replace the wires too.
    Double check the order of the plug wires on the coils 4-1-2-3 from left to right.

    My wifes old SC2 had and issue with intermittent driveability concerns with a loss of power, bucking, missing and sometimes stalling. It ended up being a back coolant temp sensor that would read correctly when I would check it but when she would take the care back it would start reading incorrectly again and cause issues with fuel enrichment and spark advance. If your ignition system looks good I would check the coolant temp sensor next. And by "check it" I mean that you should remove it and inspect the tip and electrical connection.
    -6S Resident Mechanical Forensics member #001.
    1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
    1998 F-250 5.4L triton...stock.

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