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Thread: Can't maintain a steady RPM.

  1. #1

    Default Can't maintain a steady RPM.

    Hello. I've installed my engine after a refresh and now having a very odd issue. After checking the Cranking Timing and adjusting the crank trigger, I then moved onto do my static timing check, which was on point. Now, I'm trying to rev the engine to check Inductive Delay. However, I cannot maintain a constant rev. When I place my foot on the gas pedal and press lightly to rev the engine, once it gets to about 2500-3000 RPM, the RPM automatically goes all the way down to idle and then back up again to 3000 RPM and will continuously bounce up & down until I remove my foot from the pedal. I'm lost on what could be the issue. Nothing has changed since I refreshed the engine except that I have new NGK plugs with no resistors. Could this be the problem? I've done a System Log of the issue, and tried a datalog, but the datalogs are all blank, so that's a different issue. I called Holley tech and they seem to want a datalog so I need to get that working as well. I was told that clearing all the datalogs and text files out of the Holley could help. Also wanted to point out that the IAC is disabled and I have the system set to Open Loop. Thanks in advance.

    SBC 434 N/A
    Dominator
    CNP - Holley coils
    MSD crank trigger with Hall-Effect sensor - Digital Falling
    MSD cam sync plug - Digital Falling

  2. #2
    Join Date
    Dec 2009
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    Connecticut
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    23,067

    Default

    Quote Originally Posted by emueller View Post
    Also wanted to point out that the IAC is disabled...
    Then it's not the IAC air.

    ...and I have the system set to Open Loop.
    The Base Fuel Table was probably never tuned, and was relying on the WBO2 sensor in Closed Loop.
    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

    Danny, how can the system rely on the WBO2 sensor when the system is set to Open Loop? I do not understand your last comment.

  4. #4
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    Did you previously have it set to Closed Loop? (I assumed so.) If so, that's why it doesn't like Open Loop now.
    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.

  5. #5

    Default

    Yes, the previous engine was using WBO2 sensors at 2500 RPM. I now have fender exit headers and waiting to have the collector extensions welded so they will protrude passed the fender. Right now, there is only 4 inches between the WBO2 sensor and the end of the collector. I had to pull some fuel out of the Base Fuel Table to get it to idle, but I have since smoothed that area. What are my options to get this to work for now without using the WBO2s? I need to tune the Base Fuel Table better?

  6. #6
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    Dec 2009
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    Connecticut
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    23,067

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    Quote Originally Posted by emueller View Post
    What are my options to get this to work for now without using the WBO2s? I need to tune the Base Fuel Table better?
    Yes, exactly.
    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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