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Thread: Misfire/Lack Of Power

  1. #1

    Default Misfire/Lack Of Power

    Hi. I'm running an HP EFI system with a 900 cfm 4BBL TBI throttle body on a marine 454 BBC. The boat has been running OK for the last couple of years. However recently, above 3200 RPM, it won't take any more throttle (about 2/3 open) without developing a slight misfire, and the engine runs out of power. Running without the spark arrestor, I can see that at the point the secondary butterflies open (about 3200 RPM), the rear injectors are introducing very little fuel.

    I have just replaced the fuel pump & filters, and added a manual fuel pressure gauge to compliment the fuel pressure sensor I have plumbed in. Just reset the the fuel press at an average of 21 psi between the two.

    Running with the Gauge Panel enabled, I can see that when the problem occurs, the MAP shoots up to 100 kPa. What should I look for? Vacuum hose leaks? Failed MAP sensor? Or others sensors? How can I check? Suggestions please.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    23,387

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    Quote Originally Posted by scarron View Post
    However recently, above 3200 RPM, it won't take any more throttle (about 2/3 open) without developing a slight misfire, and the engine runs out of power.
    Do the Learn Table values look like they've been corrupted from a defective WBO2 sensor?
    If the Learn Table values are corrupted from a defective WBO2 sensor, the Learn Table must be cleared.
    If the engine runs properly every time you upload a "known to be good Global Folder", maybe the WBO2 sensor is defective.
    If so, try running the engine in Open Loop mode to ignore the WBO2 sensor. If it continues to run fine, it's a WBO2 sensor issue.

    Running without the spark arrestor, I can see that at the point the secondary butterflies open (about 3200 RPM), the rear injectors are introducing very little fuel.
    Maybe you can swap the primary & secondary fuel injectors, to determine if they're the problem.

    Running with the Gauge Panel enabled, I can see that when the problem occurs, the MAP shoots up to 100 kPa. What should I look for? Vacuum hose leaks? Failed MAP sensor? Or others sensors? How can I check?
    View the sensor values on the EFI software Data Monitor, and review a datalog of this occurrence.
    http://forums.holley.com/showthread....s-amp-Datalogs (Datalog & System Log Information)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

  3. #3

    Default

    OK, seems to be fixed.
    1. I removed the injectors, took the screens off and cleaned them all with spray carb cleaner, there were a few gummy deposits. I reassembled them and swapped the primaries with the secondaries, in case there was any issue. I also dosed the tank with Wynns petrol [gasoline] system cleaner.

    2. I fitted a new WBO2 sensor, had to use a Bosch LSU, as the Holley ones with the calibrated resistor are not available in Europe. Also fitted an Innovate HBX-1 stand off adapter as the wet exhaust on the boat kills O2 sensors for a living.

    3. Cleared down the Learn Tables as Danny suggested, and started tuning again from my most recent maps. On the first couple of runs, it was still fairly rough, but smoothed & Transferred Learning To base map a few times, and it soon improved.

    Its now running better than ever before, and I have put it into Open Loop, as the WBO2 sensor was getting encrusted with salt deposits. So it looks like I need to experiment more with the tailpipes to try to stop the calling water reverting.

    Thanks for your help Danny.

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    23,387

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    Quote Originally Posted by scarron View Post
    Thanks for your help Danny.
    You're welcome, and thanks for the update.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 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, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 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 tires.

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