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Dual tank pump

Discussion in 'Engine & Performance' started by Jerry phillion, Apr 29, 2018.

  1. Jerry phillion

    Jerry phillion Full Access Member

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    My 87 swb has dual fuel ranks. Pass tank has been disconnected before I got it.
    Where is fuel pump located. Mine is a 350/tbi. Also, where are all fuel lines located.
    Would like a diagram of where and how they are run. Please make it simple.
    I have a slight fuel leak I have to find and fix. Thanks. Jerry
     
  2. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

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    pumps are in the tanks on a tbi. if tbi is anything like carbed trucks, fuel lines will run across the crossmember just below the gap between the cab and the bed, then along side the passenger frame rail, then up about where the front passenger wheel well is. if you need to do any significant work, it'll all be easier with the bed off the truck; but you can drop the tanks as well. @1987 GMC Jimmy knows the tbi stuff pretty well and is on here often.
     
  3. 1987 GMC Jimmy

    1987 GMC Jimmy Automobile Hoarder

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    All that sounds right to me. I’ve got the single 31 gallon tank in mine so I’m not as familiar with the fuel lines on the pickups, but I have dealt with them on a carbed square, and that’s what I saw. I can tell you that the senders on the pickups are not four line senders like on Blazers and Suburbans so you only have three lines on each tank: feed, return, and vent. I’m assuming that the other tank was taken offline because of the leak you mentioned or because it was failing to switch over. Where is this leak at? Really nasty rust is gonna cause leaks in the tank or possibly even fuel lines, but if it’s not that, it can be leaking right at the sender o ring, line connections, or the valve.
     
  4. Jerry phillion

    Jerry phillion Full Access Member

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    Thanks guys. I may have not been real clear. First, my pass tank
    Has been disconnected. Second, Which tank has the pump in it?
    Third, truck is not rusty, so tanks and lines look real good. fourth,
    Say the pump is in drivers tank, where does the gas travel to
    From there? It must bypass pass tank somehow. I will address
    The leak tomorrow. Thanks. Jerry
     
  5. 1987 GMC Jimmy

    1987 GMC Jimmy Automobile Hoarder

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    Each tank has a pump. The intersection of the two circuits occurs at the valve.
     
  6. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

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  7. Jerry phillion

    Jerry phillion Full Access Member

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    Thanks for the replies. Had truck on hoist this morning. Have a slow leak from pass tank, slight dripping from tank parting
    Line. The mech said it was leaking from top of tank. Is it coming
    From switching valve or o ring. Probably will have to pull tank.
    What do you think?
     
  8. Frankenchevy

    Frankenchevy Supporting Member Supporting Member

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    So it’s leaking from the tank you aren’t using?

    Clarify what you mean by tank parting line on top of tank so someone can help.

    There will be three lines going into the sender on top of each tank. A larger supply, a medium return and a vent line.
     
  9. Jerry phillion

    Jerry phillion Full Access Member

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    Yes it's leaking from tank I'm not using. As far as tank parting line I mean where the two halves are welded together. I think I Am
    Understanding this setup. The fuel is pumped from the drivers
    Tank to the valve on the passenger tank. Depending on the switch on the dash, it either stops there or continues to engine . If the fuel Is shut off there, flipping the switch on dash tells the pass tank to pump fuel to engine. Am I close?
     
  10. Zoomalot

    Zoomalot Full Access Member

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    Both tanks have individual pumps.
    They are hooked to a selector valve (not on the tank) which controls fluid routing.
     
  11. Jerry phillion

    Jerry phillion Full Access Member

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    Thanks guys. I'm trying to soak up all this good info. I have one more question. With the 3 steel lines coming from drivers tank to pass tank, are the lines connected direct to the sender or are they
    connected by rubber hoses? as a note, my pass tank power line is unplugged and looks like the ground wire is also. Probably tank
    Pump is bad, that's why tank is disconnected. Just guessing.
    One more thing. If connecting hoses are rubber, and maybe
    Leaking, will the tank have to be dropped to replace ? Taking
    It to the repair shop monday. Thanks again.
     
  12. 75gmck25

    75gmck25 Full Access Member

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    This is the setup used on a carbureted system with mechanical fuel pump. I'm not sure how they changed it with a TBI system, since the pumps are then in the tank.

    I'll attach a picture I took of the six port setup on a donor carbureted truck in the junkyard.

    - The right side of the picture is toward the front of the truck, and you can see the three lines going forward. They all run up the frame rail to a point near the mechanical fuel pump. Then there are two short hoses running over to the fuel pump (fuel feed and fuel return), and one longer hose that goes to the vapor recovery tank.

    - The line with the T fitting next to the switching valve is the vent line. The large diameter metal lines on the switch are fuel feed, and the slightly smaller lines are the returns.

    - The 3 crossover metal lines are bolted to a metal support that runs across the mounts on the frame. My truck did not have that support because it did not have factory dual tanks. I just bolted the bracket for the lines to the same support where the cab support it bolted, and then added some plastic ties to keep it stable.

    - On the far left you can see a bright purple/red color, which is the wiring that runs across to the fuel switch.

    - Wiring path - On my '75 truck, where the "main" tank was the passenger side, the dual tank switch wiring comes through the firewall with a big muliplug (4 wires?), then down the driver's side frame rail, and then across the undercab brace to the passenger side tank. They may have changed the path in later years when the main tank was moved to the driver's side.
    When my truck only had the original passenger side tank, the sending unit wire just ran down the passenger side frame rail from the gauge directly to the tank sending unit.

    Bruce


    PDRM0789.JPG
     
    Last edited: May 3, 2018
  13. hatzie

    hatzie Full Access Member

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    That's an excellent overview of the fluid routing.

    This is how the electrical portion of the 1981-1991 Auxillary Fuel Tank Regular Production Option NL2 works.
    I posted this on another board.
    **1981-1991
    Motorized Valve system... used a six port motorized valve made by Pollack. These are still being produced by Pollack on Jan 1st 2018.
    • The "universal" valves that claim they're three port usually have all three return line ports capped. You can use either just be sure to cap any unused ports to keep dirt out of the valve guts.
    • The later motorized valve remains in the last switched position unlike the earlier solenoid valves.
    • Pollack 42-159 Motorized valves are available with 65PSI limits for some, but not all, later EFI systems. The originals were rated for lower pressures.
    [​IMG]
    Electrical;
    • The Pollack valve uses five of six cavities in a Six position Weatherpack plug. A-E are used. F is plugged with a seal.
    • Internal to the valve are two diodes to prevent power being routed to the motor from D or E once the valve shuttle has reached the end of its' travel.
    • The motorized valve has a SPDT switch to control which sender feeds the gauge shortening the wiring considerably.
    • *The gauge/Sender wires are on positions A, B, & C of the valve.
    • **Senders from the tanks are on switched terminals A & C.
    • **The gauge output is on Terminal B. This wire runs to the molded sender wire connector on the RH frame rail. This allowed GM to just drop in the NL2 as a sub harness without having two main harnesses.
    [​IMG]

    Motorized tank switch details...

    • [​IMG]
    • The above switch depiction is a Polarity Reversing DPDT switch used to turn a DC motors forward or backward depending on position. GM used a proprietary switch but this exposes what the GM switch actually is doing.
    • Two of the switch contacts do not have terminals. These contacts are bridged back to the other switched terminals diagonally across the switch.
    • Output to the DC motor in the valve comes from the common terminals of the switch.
    • Power and Ground run to one switched terminal of each half of the switch.
    • When the switch is toggled to the opposite position the LH & RH MOTOR terminals of the switch reverse polarity. + becomes - and - becomes +. The valve motor then runs in the direction dictated by the polarity it's receiving on D & E til the stop on the valve shuttle cams the internal gauge and motor switches over to the switch leg with a diode that blocks the incoming current. The motor then stops til the dash switch is toggled back to the opposite position.
    • You can see below that... On the 1987 RV series TBI trucks the selected fuel pump receives Power on the wire from the switch so it will activate because it has power and the shared frame ground. The UN-Selected pump receives Ground on the wire from the switch thus shutting it down because it now has two ground wires and no power.
    The following three panes should be pretty decent visuals of what I was saying with the last two above bullets.
    NOTE: Stock 1981-1986 & Diesels don't have a 2 position Weatherpack disconnect at the sender with Fuel Pump Power (just a single sender wire from A or D on the valve), and obviously no in-tank fuel pumps, they are otherwise identical in function to the TBI setup.
    TBI TANK SWITCH SET TO RH
    [​IMG]
    TBI TANK SWITCH SET TO LH
    [​IMG]
    1981-1986 & 1981-1991 Diesel TANK SWITCH SET TO LH
    [​IMG]
    NOTE ON SWITCHES:
    • Usually, but not always, the switch is at fault for a non operational valve. The switch is cheap as in $10-$15. Change it if the wiring looks OK and the valve doesn't work.
    • 1981-1991 I ALWAYS REPLACE the motorized valve switch with the 1987-1991 RV series AC Delco D7809 or Standard DS-1807 1987-1991 R/V 10-30 "TBI" ON-ON switch. I never have been able to figure out why GM used a centre off switch on the early 80's trucks... The Pollack motorized fuel valve always had the over-travel protection diodes and switch built in.
    • For those of you that want a "Correct restoration" 1981-1986 GM used The AC Delco D7003 Momentary ON-OFF-ON switch that has "DEPRESS FULLY" emblazoned on the bezel. I NEVER USE THE D7003 SWITCH... IMHO it's a problem child because of the momentary action.

    1987-1991 RV series TBI Fuel Pump Relay for TBI tank switch and fuel pumps.

    Year specific information can be found in the 1987-1991 Emissions and Driveability service publications. You can find them in my manuals post in the Library.

    The TBI fuel pump relay (AC Delco 158240 Multi-Purpose SPDT Relay) can be found on the firewall between the transmission tunnel and the Heater/AC box.
    Fuel Pump relay without the transmission kickdown relay. You can see the pump test terminal dangling beside the split loom.
    [​IMG]

    A Hot Start Fuel Pump Controller is mounted behind the dash on some 5.7L and all 7.4L TBI trucks.
    [​IMG]
    More pictures of the harness plug behind the instrument panel are in this thread. -->http://67-72chevytrucks.com/vboard/showthread.php?t=757299

    RV series TBI Fuel Pump Relay test terminal.
    The Fuel Pump Test Terminal that's present on all RV series TBI trucks is shown pulled away from the harness.
    This picture also includes a transmission kickdown relay mounted next to the fuel pump relay. The kickdown relay is supposed to be mounted nearer the RH side of the engine bay (US passengers' side) on the tabs. The two relays are the same part and it's been 30 years, give or take, since it rolled off the assembly line...
    You can also find this AC Delco 158240 multi-purpose SPDT sealed Metripak 280/630 relay and mounting tab used elsewhere in the engine bay for DRL on some Canadian models, Aux cooling fan, Glow Plug Inhibit, and probably other things. The replacement plug is a Delphi Metripak hybrid 280/630 # 12052287 or AC Delco PT1115 is the plug with a repair pigtail.
    [​IMG]

    Fuel Pump Relay Control

    • When the ignition switch is turned ON the Electronic Control Module (ECM) will energize the coil in the fuel pump relay. The ECM will energize the fuel pump relay coil as long as the engine is cranking or running and the ECM is receiving distributor reference pulses. If there are no reference pulses the ECM will cut power to the fuel pump relay coil within 2 seconds after ignition ON.
    • As a backup system to the fuel pump relay, the fuel pump can also be turned on by the oil pressure switch. The oil pressure switch is, normally, open and closes when oil pressure reaches about 28 kPa (4 psi). Fuel Pump Power through this switch is also cut if the engine stops running as the oil pressure will drop.
    • If the fuel pump relay fails, the oil pressure switch will run the fuel pump to allow you to drive to a safe location and repair the problem. However. You will experience extended cranking times because the fuel pump will not run at all til the starter builds oil pressure. This will shorten oil pressure switch and starter lifespans if the failed fuel pump relay is not diagnosed and corrected.
    • The pump will deliver fuel to the Throttle Body where the system pressure is controlled to about 9 to 13 psi. Excess fuel is returned to the fuel tank by the pressure regulator.
    • A Hot fuel module is used on all 7.4L and some 5.7L engines to correct a hot restart (vapor lock) during a high ambient temperature condition. It is designed to over-ride the ECM 2 second pump operation and will run the fuel pump for 20 seconds at initial ignition switch "ON”.
    • The dual tank switch harness connects switch power at the "Bulkhead Connector", replacing the fuel pump power wire with the NL2 harness, in the below Fuel Pump Relay schematic.
    [​IMG]


    All years NL2 system NOTES:

    • Since the 1975/76-1991 NL2 dual tank systems used a sub-harness that plugs into the RH tank sender wire on the RH frame rail and power comes from the fuse panel under the dash or the TBI fuel pump power connector. It's fairly easy to retrofit and or update to a later model system.
    • You can swap a 1981 -1991 motorized Pollack valve sub harness into a 73-80 truck. You need the entire later model NL2 sub harness from the fuse panel/ground bar to the dash switch. Two wires run through the firewall to the valve and one wire from terminal B of the valve to the RH frame rail disconnect of the "production tank" sender wire.
    • BTW I've used the Delphi Packard 56 switch plug for a 73-80 system on a generic polarity reversing switch and rolled my own harness to convert a single tank truck to a dual tank truck. Much easier to drill a 1/2" hole for a generic polarity reversing toggle switch than cut and file a square hole for a GM rocker switch. The toggle pointed to the enabled tank so no bezel was required.
     
  14. Jerry phillion

    Jerry phillion Full Access Member

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    Thanks Bruce and David. This is what I was looking for.

    Jerry
     

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