Results 1 to 8 of 8

Thread: Fuel Pump (green wire) activation without power leads connected?

  1. #1

    Default Fuel Pump (green wire) activation without power leads connected?

    With the HP EFI setup, is it possible for the fuel pump wire (green) from the main harness to be activated by a lead on the auxiliary Input/Output harness, without the primary power leads for the EFI being connected (large black & red wires).

    Car has just had a complete rewire and I have not gone in & reprogrammed any of the I/O ports yet. All leads are connected except the heavy black/red battery leads for the HP EFI. The red/white striped wire is seeing +12V with ignition on toggle switch. I have my fan wired such that I can activate it via a toggle switch, or via the ECU when connected to one of the auxiliary harness leads. When I went through initial testing last night, when I flipped the +12V switch for the fan, the fuel pump turned on as well. Is it possible that the ECU is just mapped to output +12V to my fuel pump relay via the green wire when it sees +12V on the fan wire input, even without the main power leads connected?

    Just want to rule out the possibility of having a short somewhere, but I didn't think the ECU would work in that capacity without the main power leads being connected. Thanks in advance!

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,903

    Default

    No, the system relay won't activate without the main power harness connected. The system relay is ECU activated:
    http://forums.holley.com/showthread....9623#post69623 (System Relay & Injector Wiring Troubleshooting)
    http://documents.holley.com/techlibr...10555rev17.pdf (For Reference - Holley EFI Wiring Manual, Section 13 "Wiring Appendix")
    http://documents.holley.com/techlibr...10555rev17.pdf (For Reference - Holley EFI Wiring Manual, Section 2.1 "ECU Pin-Outs")
    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

    Not what I wanted to hear. Currently, the fuel pump has a standard four prong relay, with the +12V activation coming from the green harness wire (A2). The fan is also on a separate relay, except the +12V to activate the relay has a jumper to B12 yellow/gray I/O harness. I'm stumped as to how one is energizing the other. I should clarify that I'm using the system to activate an external +12V relay, due to a high fuel pump draw.

  4. #4
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,903

    Default

    Quote Originally Posted by Supe View Post
    I should clarify that I'm using the system to activate an external +12V relay, due to a high fuel pump draw.
    Simply use the green fuel pump wire (+12V) to trigger your additional fuel pump relay's coil (+) terminal #86. Relay coil terminal #85 is ground.
    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

    That's how it's currently configured, which is why I have no idea how the green wire is becoming energized via the fan circuit.

    So I went back and did a few checks. When I disconnected B12 to the I/O harness, the fuel pump stopped engaging with the fan.
    With B12 connected and the fan on, I was getting about 8V out of A2 (green wire), enough to trigger the fuel pump relay.
    I then connected the main power harness to the ECU. With B12 connected and the fan on, the fuel pump
    was no longer engaging (it did prime for 5 seconds when toggling the ignition on, and saw a full 12V).
    I checked voltage across A2, and I'm seeing about 3V. I then disconnected the Auxiliary I/O Harness, and I'm seeing about 3.3V across A2 green.

    So it seems that no matter what, as soon as the system sees 12V switched, I'm getting a 3.3V reading across the green A2 wire. Is this normal? I would have expected to see nothing until the ECU engages the fuel pump. I double checked all the grounds and they appear fine. (I run EVERYTHING, but the ECU main power harness to a common ground pass-through stud which goes straight to the battery negative, battery negative then runs straight to a welded chassis ground). No obvious shorts or +12V wires chafing anywhere. Everything was plug & play with the ECU with the exception of the SBC DIS conversion coils, which I pinned into the connector per the instructions.

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,903

    Default

    Quote Originally Posted by Supe View Post
    ...I'm getting a 3.3V reading across the green A2 wire. Is this normal? I would have expected to see nothing until the ECU engages the fuel pump.
    That's normal for key-on/engine-off, after the five second Fuel Pump Prime time. The ECU fuel pump output voltage doesn't actually drop to zero.
    I suggest you connect everything as it's supposed to be (including the ECU main power harness), and see if the fuel pump issue persists.
    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.

  7. #7

    Default

    Thanks. As long as the ECU main power harness is connected, it functions normally with no interference from the fan circuit. If the residual 3V across that wire is normal, we're good to go. Thanks for the help!

  8. #8
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    22,903

    Default

    Quote Originally Posted by Supe View Post
    As long as the ECU main power harness is connected, it functions normally with no interference from the fan circuit.
    Yep, I thought so.

    Thanks for the help!
    You're welcome.
    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.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
About us
Holley has been the undisputed leader in fuel systems for over 100 years. Holley carburetors have powered every NASCAR® Sprint® Cup team and nearly every NHRA® Pro–Stock champion for four decades. Now, Holley EFI is dominating the performance world as well as our products for GM's LS engine. Holley's products also include performance fuel pumps, intake manifolds & engine dress–up products for street performance, race and marine applications. As a single solution, or partnered with products from other Holley companies - Hooker Headers, Flowtech Headers, NOS Nitrous, Weiand, Earl's Performance Plumbing, or Diablosport - Holley products can give you the edge you need over the competition.
Join us