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Thread: Missing/Rough idle when fuel pump is running.

  1. #1
    Join Date
    Oct 2019
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    Sykesville, MD
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    Default Missing/Rough idle when fuel pump is running.

    Hello all, new member and first post here. A little background. Blueprint 454 small block running Super Sniper 8 injector and HyperSpark ignition/coil/distributor.

    Yesterday was the first time firing the engine since receiving it and installing Holley EFI. The engine fired up right away, but was running very poorly and eventually sputtered out. Fuel prime went perfectly, fuel pressure at 62 psi at prime and while running, timing was set and verification of spark to all plugs. After scratching my head for a while I did a bit of research and thought I was possibly having am EMI issue.

    I began separating harnesses and looms, although in hindsight I don't believe this to be my issue. During the course of all this I decided to disconnect my fuel pump power via a Weather-Pack connection I had installed inline, since I didn't want to be flooding the engine while cranking & "testing". As soon as I cranked the engine with the fuel pump power disconnected the engine fired and ran perfectly on all 8 until it starved for fuel. I reconnected the fuel pump and the same missing/stuttering occurred.

    My first inclination was that the pump was possibly grounding on the tank/frame somehow and that was throwing the ignition system off. After a few more tests I decided to drop the fuel tank and run the pump from a completely separate 12V source. At this point the only things connecting the fuel tank/pump to the rest of the vehicle were the supply and return hoses. I thought I'd have a resolution but no luck, the same problem occurs when the fuel pump is running.

    My next thought was possibly some kind of RFI from the pump, but then I decided I didn't want problems that big so I dialed my logic in and considered there may be an issue with my injectors? Under pressure the engine doesn't run properly, but as the pressure bleeds off everything runs perfectly. I setup a switch to quickly turn the fuel pump on an off remotely and sure enough as soon as the system reaches 62 psi constant pressure the engine begins to miss.

    I spoke with Holley tech support for a while while troubleshooting and we were in agreement it had to do with some kind of power/grounding issue with the fuel pump, but now that I has eliminated that as the potential culprit I'm curious if anyone has further advice. Possibly a clogged injector that relieves as the pressure bleeds?

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    Default

    Quote Originally Posted by Cucktales69 View Post
    During the course of all this I decided to disconnect my fuel pump power via a Weather-Pack connection I had installed inline, since I didn't want to be flooding the engine while cranking & "testing". As soon as I cranked the engine with the fuel pump power disconnected the engine fired and ran perfectly on all 8 until it starved for fuel. I reconnected the fuel pump and the same missing/stuttering occurred.
    Seems the Sniper EFI Base Fuel Table (base calibration) is too rich for your engine. Disconnecting the fuel pump leans it out and it runs good momentarily.
    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
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    Oct 2019
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    Sykesville, MD
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    Thank you for the response Danny. I hadn't even considered that possibility. How would I go about adjusting the fuel table? I can't even run the engine long enough to bring it up to temp.

  4. #4
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    Connecticut
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    No. You'd do it key-on/engine-off, click "Save" and cycle the key off/on.

    If you'd like to manually tune the Base Fuel Table (even while the engine is running), read below:
    Left click & drag to select a group of cells, then use the CTRL & Arrow keys (▲►▼◄) to change the highlighted cell values.
    The ▲ & ▼ arrow keys adjust the Base Fuel Table slowly (one tenth at a time). The ◄ & ► arrow keys adjust it rapidly.
    Or you can left click & drag a group of highlighted cells, and right click "Offset Selected" to adjust the entire cell group.

    https://forums.holley.com/showthread...241#post214241 (Related Forum Thread)
    https://forums.holley.com/showthread...118#post210118 (Related Forum Thread)
    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

    Are you laptop tuning Cucktales?
    69 Camaro
    400 SBC, ProCharger D1SC
    1.302 60', 5.95@116.4 on pump gas

  6. #6
    Join Date
    Oct 2019
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    I'm laptop tuning now. Slowly learning my way around the interface. My only concern is that the stock cam base tune is far too rich to run? Seems strange to me.

  7. #7
    Join Date
    Dec 2009
    Location
    Connecticut
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    Quote Originally Posted by Cucktales69 View Post
    I'm laptop tuning now. Slowly learning my way around the interface.
    http://documents.holley.com/techlibrary_199r11259.pdf (Holley Sniper EFI Help Manual - EFI Software, Tuning & Datalogging)
    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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