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Thread: Ford 351C Exhaust Popping

  1. #1
    Join Date
    Sep 2010
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    Default Ford 351C Exhaust Popping

    Ford 351C, Automatic Transmission, Mild Cam, Holley Sniper EFI with Ignition Box & Distributor.
    In park, if I hold the throttle at a consistent RPM I get a lot of popping out the exhaust and the engine runs very rough. Consistent with a misfire. At idle, the engine runs fine. I've attached a datalog and Config File. The only thing that looks out of whack on the datalog is the AFR spikes lean, which could correlate with the popping sound. However, I did notice that If I thump the throttle the exhaust is black, which would be consistent with running too rich.
    351C.sniper.zip
    351C.dl.zip

  2. #2
    Join Date
    Dec 2009
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    Since you can isolate it, see if AFR or timing changes affect it.
    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.

  3. #3

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    Scott, good news is everything looks OK. Bad news is you might have a plug wire crossed or something outside of your tuning. The only thing I noticed is you're off the Base Timing Table and Target A/F Ratio table as in you're below you MAP range value on the Y-axis. I'd go in and rescale the MAP range so the Sniper can utilize more of the table. Have you verified Static Timing with the HyperSpark? I don't see your Base Timing or Target AFR being too far off. Maybe an exhaust leak too?

  4. #4
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    http://forums.holley.com/showthread....4365#post44365 (MAP kPa & RPM Axis Configuration/Tuning Information)
    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.

  5. #5
    Join Date
    Sep 2010
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    Quote Originally Posted by Danny Cabral View Post
    Since you can isolate it, see if AFR or timing changes affect it.
    I tried changing both, going richer and leaner produced the same results. Timing was originally set at 18° tried 14° & 24°, same result.
    I'll take a look at the link, thank you.

    Quote Originally Posted by thecowwatcher View Post
    Scott, good news is everything looks OK. Bad news is you might have a plug wire crossed or something outside of your tuning. The only thing I noticed is you're off the Base Timing Table and Target A/F Ratio table as in you're below you MAP range value on the Y-axis. I'd go in and rescale the MAP range so the Sniper can utilize more of the table. Have you verified Static Timing with the HyperSpark? I don't see your Base Timing or Target AFR being too far off. Maybe an exhaust leak too?
    I'll look into rescaling the tables. I kind of agree with you at this point, that it's something external or some kind of interference. I did verify static timing and it's spot on. I don't hear an exhaust leak, but that doesn't mean there isn't one. The car is pretty loud. Thank you for the advice.

  6. #6

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    I didn't notice interference in the datalog. Your CL Comp, TPS, IAC & timing are relatively normal when you hold the throttle open. That's why I'm thinking something external. Hopefully it's a relatively easy fix, it's finding the problem that's the hard part.

  7. #7

    Default

    The pop & cracking is coming from it being too lean, but the question is why? Does is ever miss when under a load while driving? I concur with previous statements, I'm inclined to think you have a mechanical issue happening. Without me being there, my first two guesses are secondary ignition issue or exhaust issue before WBO2 sensor. Let us know what you find.

  8. #8

    Default

    I'd look for a vacuum leak, bad plugs, bad plug wires, etc. Double check all of the easy stuff first. Do not assume that anything is correct, confirm it before moving on. It could be something harder to find such as a retarded camshaft or worn lobe on the cam or something like that, but those things are more difficult to track down.

  9. #9

    Default

    I would add crossed plug wire as another thing to look for. Did you verify static timing and rotor phasing (if Sniper controlled timing). My guess is it's not tune related, but mechanical. You can run a compression check as well.
    69 Camaro
    400 SBC, ProCharger D1SC
    1.302 60', 5.95@116.4 on pump gas

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