Not much voltage at fuel pump connector
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  • 1 Post By j2rossit
RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Not much voltage at fuel pump connector in Past Cadillac Vehicle Discussion; Just to make sure the fuel pump was getting power, I took a multimeter and checked the voltage at the ...
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    nebulosity's Avatar
    nebulosity is offline Cadillac Owners Fanatic
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    Not much voltage at fuel pump connector

    Just to make sure the fuel pump was getting power, I took a multimeter and checked the voltage at the connector when my husband turned he key to the on position, and the highest voltage reading we got was something like 30mV. We checked the power to the fuel pump relay, and the relay shows that the fuel puml should get an initial voltage of ~12 volts for 2 seconds. Does this sound like there is a short somewhere brtween the fuel pump relay and the fuel pump? Or is the voltage really stepped down that low at the fuel pump? ('84 deville, 4.1) We got a new fuel pump to replace the other one, but before we do that, we want to make sure the fuel pump is getting he power itssupposed to have.

    The fuel pump fuse is intact (verified with multimeter), and we tested the computer's diagnostics--it throws a 20 with the fuel pump connecor disconnected, and when reconnected, the code 20 doesnt come back. The only other error Im getting is 14, which is he coolant sensor, and ive ordered one to come in today at 3:30 but i assume the coolant sensor functionality shouldntd interfere with the ful pump.

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    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Not much voltage at fuel pump connector

    I would check the Ohm resistance to ground. The supply pin on the connector will read a low resistance if there is a short (you don't need to turn the car on to check this).
    If I can find my FSM I can tell you the next set of steps on the fuel pump trouble shooting tree but my wife "tidied" a few weeks ago before some guests arrived and I haven't been able to find it since.
    nebulosity likes this.

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    nebulosity's Avatar
    nebulosity is offline Cadillac Owners Fanatic
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    Re: Not much voltage at fuel pump connector

    Quote Originally Posted by j2rossit View Post
    I would check the Ohm resistance to ground. The supply pin on the connector will read a low resistance if there is a short (you don't need to turn the car on to check this).
    If I can find my FSM I can tell you the next set of steps on the fuel pump trouble shooting tree but my wife "tidied" a few weeks ago before some guests arrived and I haven't been able to find it since.
    Thanks so much!
    I found the tree youre talking about in my FSM and we went through the rest of the debug steps. Somehow along the way I started to see 12 volts at the wiring harness, so i must not have been doing something right. We went ahead and replaced the fuel pump and now Im getting fuel tothe injectors, yay!!!!! the spray is weak though, so ill have to see if injector cleaner helps, or maybe even rplace the injectors (throttle body was disassebled, cleaned and rebuilt last year, so thats good. Thanks for your help!

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    j2rossit is offline Cadillac Owners Enthusiast
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    Re: Not much voltage at fuel pump connector

    It made me happy cause I finally got the motivation to force my wife to sit down and think as to where she might have put the book. I finally found it in the basement hidden under a box sitting on an extra coffee table we have.
    Now I can look up what's involved in the next projects I want to do

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