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Thread: Misfire at different RPM - wondering if MSD ignition box could be bad?

  1. #1

    Default Misfire at different RPM - wondering if MSD ignition box could be bad?

    Having problem with rough running and misfire. Distributor is new Pro Billet model 8546, new Blaster 2 coil and older 6AL box.
    If you swap the leads from the box to the distributor around, the car runs rough up to about 2000 RPM then smooths out.
    On the other hand, if they are reversed it runs smooth up to about 2500 RPM then starts to run rough.
    Plugs are also new Champions and plug wires are fairly new Taylor wires. Car is '67 GTX with mild 440. Thanks, Bill

  2. #2


    Where is the box grounded? And how is that coil mounted? (Laying on its side, at an angle, or straight up?) Also, have you measured OHMS on the magnetic pickup?

  3. #3
    Join Date
    Dec 2009


    And sometimes a distributor's pickup coil intermittently fails the Ohms resistance test.
    Read page 2: (MSD Magnetic Pickup Testing)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  4. #4


    Yes, exactly right.

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