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Thread: Odd intermittent rough running problem.

  1. #1

    Default Odd intermittent rough running problem.

    Have a LSx with a Holley Dominator running V4.0 Build 110 software. Normally it runs great, but occasionally (like 1 out of 20-40 starts) it will run real rough, and checking the exhaust with thermal camera it's obvious that a couple of the cylinders are not running. Checking the injectors with noid lights shows the injectors on those cylinders are not firing, but (from memory), the coils are. Normally I'd think it's a wiring issue (loose connector, etc.), but the odd thing is, when it does it, it isn't the same cylinders every time (from run to run). It moves around! I've attached a datalog file from one of the bad runs, if anyone can gleam some information from such? Thanks in advance! Mike
    Attachment 3106

  2. #2


    Welcome to the club. I've experienced the same issue. I have not figured out the problem yet. By rough, do you mean it's misfiring? Also in the datalog, I noticed the TPS is 18% and your RPM is around 1100 RPM, that seems odd to me.
    Last edited by Joeyman; 05-08-2018 at 01:00 PM.
    89 Mustang GT
    Dart Block 363 with Borg S475 Turbo
    Holley Dominator EFI with 7" Digital Dash

  3. #3


    Thanks Joeyman. I wouldn't say misfiring, because the cylinders that are cold don't fire at all. The other cylinders fire fine. Normally the idle is not that high (1100 RPM). You'll also notice from the datalog that one oxygen sensor shows way lean (20-22 AFR), whereas the other shows much less lean (around 17). When it's running normal (all cylinders firing) the engine idles around 850 RPM, and the AFR at idle is in the 13-14s.

  4. #4
    Join Date
    Nov 2016
    Metro Detroit


    Do you have a ground cable from the battery to the block? I had a similar intermittent issue, and that solved mine.

  5. #5
    Join Date
    Dec 2009

    Default (Troubleshooting Checklist - Holley EFI)
    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.

  6. #6


    Same issue. I have grounds everywhere. Same every 20 starts or so, it'll misfire really bad. A couple of key cycles and it'll go away.

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