1977 Fuel Injection help

Discussion in 'Big Block Cadillacs' started by Fleetwood, Sep 9, 2019.

  1. Fleetwood

    Fleetwood New Member

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    Recently acquired 1977 Eldorado with factory fuel injection, and trying to get it to start.
    Car cranks, I get spark, and in-tank fuel pump is running with ignition in RUN position. But the inline fuel pump doesn't run, and I get no fuel to injector rail.
    Are inline and in-tank fuel pumps both controlled by the ECU? Is spark/distributor controlled by ECU?
    Just trying to get some ideas, i'm suspecting a bad ECU/fuel pump relay, but the car is parked in the grass, and have yet to get under the car to test the fuel pump by supplying 12v to it directly.
     
  2. kzhurley

    kzhurley Active Member

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    I dont know anything about that efi, but I have the factory service manual supplements that you'd be welcome to for postage.
     
  3. DaveM

    DaveM Member

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    I know of only one expert on these systems, and that is Bruce Roe. He has a few mods that can help these systems live. But if were me, I would take the frame rail pump out and plum it straight threw. Then pull out that low pressure pump in the tank and put a high pressure pump in .And one of Bruce's mods is not to run the pump by the ECM , but just have the ECM run a relay with a new power line with a strong relay. Talking to Bruce could help you out a lot and he can repair your ECM.
     
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  4. Caddylackn

    Caddylackn Member

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    I would think the inline fuel pump relay would be triggered by the ignition switch, and not the ECU, but I do not know cadillac EFI. If the car has been sitting I would carefully clean check the connectors to the ECU, sensors, and relays, check wires for mice chewing, and clean all the grounds you can find. And of course check the inline pump and relay.

    There is also the chance the fuel rail is plugged with old jelled fuel and maybe the inline fuel pump can't pump cause it has no where for the fuel to go (assuming no fuel return line or plugged rail before fuel return line) and pops the fuel relay, or the inline pump is just bad.
    If you open up the fuel line at the inline pump to test the inline pump, use this opportunity to blow out the crud in the fuel rail out the open line and also pump out crud in the tank line from the intake pump. Is there a schraeder valve on the fuel rail for pressure testing?

    If there is a lot of crud in the fuel rail, I would remove the fuel rail and all injectors and back flush and test them and replace all the fuel filters to prevent new crud from getting in.

    There could also be a plugged fuel filter between the in-tank pump and the inline pump that would cause the inline pump not to pump. I would jump all over the offer by kzhurley and use his factory service manual to trouble shoot this. I could not find very good info. on the '77 and fuel injection diagrams on the internet
     
  5. kzhurley

    kzhurley Active Member

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    I could also scan them and send email to you. Thats if I can figure out my scanner lol
     
  6. 5one9

    5one9 Active Member

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    What vehicle(s) do you drive?:
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    Alt-Ctrl-Del
     
  7. kzhurley

    kzhurley Active Member

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    Full of info. I'm away from my scanner right now but I think I'll scan it and see if there's a way to post it for people to download it.. I suppose its legal? Lol
     

    Attached Files:

  8. Fleetwood

    Fleetwood New Member

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    I'll take that book, how much to 98233?
     
  9. kzhurley

    kzhurley Active Member

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    Pm sent
     
  10. Bruce Roe

    Bruce Roe Member

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    That is the best book on 70s Cad EFI. Can be found on Evil Bay, I also have
    spare copies. The Ign turns on the ECU, the ECU turns on pump power only
    when the engine is turning or for a second with Ign turn on, for safety. The 2
    pumps are on the same circuit, also controlled by the same circuit is the cold
    idle air valve on top of the throttle body.

    The EFI has no control over the HEI, but the SPEED SENSORS mounted low
    on the HEI trigger half the injectors on alternate crank revolutions. The pump
    circuit tends to burn out the ECU contacts, but I have a $10 kit to avoid or
    repair the problem (or make your own copy).

    I repair broken 70s Cad ECUs.
    Bruce Roe bcroe@juno.com CLC # 14630
     
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  11. Fleetwood

    Fleetwood New Member

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    Update.

    Back in October I confirmed that the inline pump is dead, got new pump, but then I accidentally shorted the pump connectors and no longer have any voltage to it. Found a blown inline fuse near the ECU, replaced it but still nothing. So I gave up.
    It's getting warm outside, so I got back to it, still haven't figured out why no voltage to pump, so I wired a the pump directly to battery. Thing started right up!
    I think at least one injector is stuck open, with pump running and engine off I hear it spraying when I open the throttle. And starter can't crank the engine anymore, must have filled cylinder with fuel.
     
  12. Bruce Roe

    Bruce Roe Member

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    You could send your ECU to get the fuel pump ckt and anything wrong
    checked out. A failed enrichment circuit can flood the engine.

    I would attach a fuel pressure gauge and momentarily run the pumps.
    pressure should go to 39psi and then hold for some seconds, unless an
    injector is leaking. Bruce Roe
     
  13. Fleetwood

    Fleetwood New Member

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    With pump running, pressure is 39psi. With pump off, instantly drops to about 36psi. Then in 5 minutes it's down to 30psi.
     
  14. Fleetwood

    Fleetwood New Member

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    The last picture is why I'm not sure I wanna spend any money on this car.
    IMG_20200313_180518.jpg IMG_20200313_180550.jpg IMG_20200313_180628.jpg
     
  15. MIHELA

    MIHELA Active Member

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  16. Fleetwood

    Fleetwood New Member

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    Video of it running... with zero fuel pressure, fuel pumps unplugged, confirmed later with fuel pressure gauge, ran for a good minute before I shut it off. When I connect the fuel pump, it definitely floods the engine and it wants to die, disconnect it and it smooths out. Must be running on fumes from fuel sitting in intake manifold.
    Now i'm not even sure the ECU works at all. And it seems there's no way to remove ECU without removing top of the dash, just one backward bolt with no way to reach it.

     
  17. Darius

    Darius Well-Known Member

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    On the positive side, your engine sound pretty darn good running with no fuel pressure!!

    For the record: I have no experience tuning or running a stock Cadillac fuel injection system - though I do own the hardware for one. Having a bit of fuel injection experience, both electronic and mechanical, what you describe makes no sense. Without going into the various elements of what is required for injection to run right, high on the list would be proper fuel pressure, and yet yours is at zero. Go figure! o_O

    Let us know what you find when you figure out what the hell is happening! But one thing should not be overlooked and that is an apparently good running engine. :)

    Best,

    bro. d
     
    Last edited: Mar 15, 2020
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  18. Cadillac Kid 1

    Cadillac Kid 1 Well-Known Member

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    With all that above I would question how you are reading the fuel pressure. If you do not have the proper connection you will not depress the schrader valve and the readings will be zero. If the car runs for 10 minutes you MUST have fuel pressure.
    Greg Surfas
     
  19. Fleetwood

    Fleetwood New Member

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    A better video. In the beginning I run the fuel pump for a few seconds, fuel pressure drops about 2psi when I turn off the pump. Then it drops even more as soon as I turn on the ignition, so I guess ECU opens the injectors there, as Bruce said it's probably a failed enrichment circuit. Runs at zero pressure (pump's off), later I go around and connect pump again for a second, engine starts to flood. In the end I ran the pump too long which flooded the engine.
    Blue gauge is oil pressure.

    I'm afraid to run the engine for longer, but I bet it's not gonna run for long with pump off. Has a few broken exhaust manifold bolts, and I can clearly see fire cracking in the gap between manifold and head, engine is dirty and starts smoking, afraid to catch it on fire.
     
  20. Darius

    Darius Well-Known Member

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    Fleetwood,

    I'm going to go along with you and Bruce on this one. After watching that video it is clear that you do have pressure with the pump wire connected and that pressure does drop with the wire disconnected. For the engine to continue to run, as well as it does, must mean that most of the injectors are firing. The run-on must be due to the residual fuel in the fuel rails having just enough pressure to exit the injectors due to a malfunctioning enrichment circuit. Basically, I think Bruce nailed the issue right out of the gate!

    bro. "impressed" d
     
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