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Thread: 1985 4-Door Brougham Fuel Injectors

  1. #16
    j2rossit is offline Cadillac Owners Enthusiast
    Automobile(s): 85 FW Brougham, 68 Wildcat 'vert, 92 & 96 Roadmaster Wagons
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    Re: 1985 4-Door Brougham Fuel Injectors

    But I've had my oil pressure sender completely disconnected and the engine still ran.
    And when the oil pump died all together, the oil pressure sender cut the circuit and the oil pressure light came on but the car kept running.
    I don't understand how that could be possible if the injectors are fed through the oil pressure switch.


  2. #17
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: 1985 4-Door Brougham Fuel Injectors

    I just took a good long stare at my 85 FSM and came up with the following:
    The oil pressure sender is a part of the fuel pump circuit. It appears that it has a "normally open" circuit that connects the positive and negative side of the fuel pump relay. So if that circuit closes, the power will short circuit through the oil pressure unit instead of the fuel pump. I'm not sure what would cause the oil pressure switch to close this circuit since closing it due to low pressure would mean the fuel pump was bypassed on start up.

    I also found a fuel injector troubleshooting guide and I'll try and post it when I get the time.

    ----------

    A quick phone call to a buddy revealed that the oil pressure switch has 2 thresholds, 1 that will turn the light on, and one really low one that will activate the fuel pump bypass circuit. So when my oil pump went, it must has still been giving just enough pressure to keep the fuel pump going but not enough to turn the light off.
    It also makes sense that unplugging the wiring harness would not stop the engine since that just forces the bypass circuit to stay open.

  3. #18
    Justsomeguy is offline Cadillac Owners Member
    Automobile(s): 1985 Cadillac Fleetwood Brougham
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    Re: 1985 4-Door Brougham Fuel Injectors

    If we remove the fuel injectors, the car will run because the fuel is getting -to- the injectors, so without the injectors in place the gas just spills out all over the place. But the injectors themselves are not spraying, so once the injectors are put back in, it won't start.

    So from my limited perspective it seems like either A. The injectors are bad or B. whatever tells the injectors to spray is bad. Or possibly C. they are getting fuel but not enough pressure, but as I said all the car people I know told me that's unlikely.

    I know they ARE getting power because when tested with a Noid Lite it did flash, so a lack of power isn't the issue.

  4. #19
    j2rossit is offline Cadillac Owners Enthusiast
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    Re: 1985 4-Door Brougham Fuel Injectors

    I went through the diagnostic chart and I think you're better off waiting for your copy of the manual to arrive. There's no way I'll be able to go through the procedures properly.

  5. #20
    Justsomeguy is offline Cadillac Owners Member
    Automobile(s): 1985 Cadillac Fleetwood Brougham
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    Re: 1985 4-Door Brougham Fuel Injectors

    Quote Originally Posted by j2rossit View Post
    I went through the diagnostic chart and I think you're better off waiting for your copy of the manual to arrive. There's no way I'll be able to go through the procedures properly.
    Haha, that's fine. Not everything can be done over the internet.

  6. #21
    j2rossit is offline Cadillac Owners Enthusiast
    Automobile(s): 85 FW Brougham, 68 Wildcat 'vert, 92 & 96 Roadmaster Wagons
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    Southern Ontario
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    Re: 1985 4-Door Brougham Fuel Injectors

    I will tell you that it all hinges on the fuel pressure reading. The chart starts with dividing the tree up between: less than 9 psi, greater than 9 psi and less than 12 psi, and finally over 12 psi.
    If it's between 9 and 12 psi and no spray from either injector, then it boils down to checking the exact voltages between the injectors to look for any imbalance. specific imbalances and polarities point to different issues with the injector circuitry.

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