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Thread: Run-On

  1. #1

    Default Run-On

    It rarely happens, but sometimes when the engine is at full temp, I shut the car off and the engine will run-on for a second or two. I'm sure the ECU is supposed to shut fuel off, so how could this happen?

  2. #2
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    Leaking fuel injector, failed intake manifold gasket, defective fuel pressure regulator (ruptured diaphragm), wiring problem.
    https://www.msdperformance.com/suppo...s/#EngineRunOn (MSD Troubleshooting - Engine Run-On)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 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
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    Quote Originally Posted by Bill71 View Post
    It rarely happens, but sometimes when the engine is at full temp, I shut the car off and the engine will run-on for a second or two. I'm sure the ECU is supposed to shut fuel off, so how could this happen?
    Engine run-on is a sign of an electrical problem. Something is wired incorrectly or is missing a relay when it should have one. You have to determine what device is causing a power backfeed that is keeping everything powered up. Typical things are usually the fans, and since it only happens when the engine is hot, I would start checking there, as they are likely to be on with the engine hot.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  4. #4

    Default

    Maybe I should clarify; when I wrote run-on, I meant dieseling. I do have two electric fans, but I used diodes after reading about them on here. BTW, the car is an old Camaro with an LS7 transplant.

  5. #5
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    Quote Originally Posted by Bill71 View Post
    Maybe I should clarify; when I wrote run-on, I meant dieseling.
    Same difference (for the purpose of this thread).
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 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.

  6. #6

    Default

    Quote Originally Posted by Danny Cabral View Post
    Leaking fuel injector, failed intake manifold gasket, defective fuel pressure regulator (ruptured diaphragm), wiring problem.
    https://www.msdperformance.com/suppo...s/#EngineRunOn (MSD Troubleshooting - Engine Run-On)
    I thought about the leaking injector. How would I verify that?

  7. #7
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    I don't think it's your problem, but you can have them tested & cleaned.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 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.

  8. #8

    Default

    Quote Originally Posted by Danny Cabral View Post
    Same difference (for the purpose of this thread).
    I thought dieseling was the engine running without spark. Some of the suggestions above are about back feeding the ignition with voltage to continue firing the spark plugs. Aren't those two different things?

  9. #9
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    I'm just looking at it as the engine continuing to run after the key is turned off.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 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.

  10. #10
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    Quote Originally Posted by Bill71 View Post
    I thought dieseling was the engine running without spark. Some of the suggestions above are about back feeding the ignition with voltage to continue firing the spark plugs. Aren't those two different things?
    I highly doubt it's Dieseling, unless you're at 14:1 compression.
    What you are experiencing is some electrical run on. It's just a matter of figuring out what's causing it.
    By the way, if by some chance you have a car stereo with a large capacitor, that can cause this situation as well.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

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