Fuel supply question

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by plumber, Jul 10, 2019.

  1. plumber

    plumber SHO Member

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    Hello. My 1993 sho has been running great lately, but this morning I notices the FP did not shut off like it always has it just kept running. The car starts and runs find so I was wondering if anything bad can happen if I keep driving like that ?
     
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  2. luigisho

    luigisho SHO Member

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    Fuel pump runs indefinitely?
     
  3. NoSlo

    NoSlo GoldMember

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    Are you saying that the fuel pump, when you first turn the key to the run position (without starting the car), runs for more than the expected two seconds?

    The car's computer controls when the fuel pump turns on and off.

    If it continues to run when the car is off, either before you move the key to "start", or after you turn the key off, then the likely fault is in the CCRM module. A sticking relay in the box with many relays.

    The CCRM gets fuel pump power from the battery, not via the key, so a bad relay should continue to have problems running regardless of the key state. Otherwise, the ECU might not be getting the signal that the fuel pump has turned on, from wiring fault or bad ECU.
     
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  4. plumber

    plumber SHO Member

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    Thank you for responding. I had some issues some time ago and got a new ccrm from shosource and ecm from A1 cardone. Always before with key in on position without starting the FP would run for aprox 2 sec and stop. But now if I leave key in on position the FP stays running. I didn't want to leave it doing that because I'm not sure what would happen. So that is why I asked if the car starts anyway is something going to happen if I leave it like that. I do not know how the pump is told what to do once car is running. Plumber
     
  5. luigisho

    luigisho SHO Member

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    First guess-- I agree with CCRM like a relay is open. Likely the result will be burning up the pump or draining the battery or taxing both and see what fails first. I'm not sure what all your issues were that required replacing both items previously. Nothing is designed to never shut off without something giving up the ghost
     
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  6. NoSlo

    NoSlo GoldMember

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    If it never stays running after you shut off the car, but when you turn the key back on it runs again in "key on" it is unlikely to be the CCRM.

    The ECU tells the CCRM when to turn the fuel pump on and off. It also has a sense line to detect if the fuel pump relay successfully turned on. It has some logic that says "run the fuel pump when the key is turned on, but if we don't start and run the engine, turn it back off".

    Something is interfering with that process in the ECU, or their could be a strange failure in the CCRM wiring where the wrong circuits are shorting out between relays.

    Inspect all the wires from the CCRM harness connector to see that nothing obvious is frayed or missing insulation. You can remove the white clip so the wires can be spread out.

    First, I would unplug the fuel pump/PCM 30A fuse in the engine compartment. Then turn on the key. If the fuel pump runs, then you've got a problem, some wire or component with "key on +12V" is shorting to the fuel pump circuit.

    If so, you can disconnect the battery so the relays won't turn on, and connect a multimeter in "ohm" setting between the pink/black fuel pump wire (which goes all the way from CCRM pin 5 back to the emergency shut-off switch and the tank) and the battery positive. This line should not have any continuity to positive when the key is turned on (should measure >10kOhms).

    Secondly, we need to see that the PCM can detect that the fuel pump has turned on; it might keep on trying if it doesn't have this signal. ECU pin #8 (fuel pump monitor, FPM) is spliced to the fuel pump power after it comes out of the CCRM pin 5, a Pink/Black wire. You can unplug both CCRM and ECU, and check for continuity at the pins, or you can probe the correct ECU pin wire at the back of the plug to detect 12V when the fuel pump runs.

    Then the choice of the SHO owner that has many parts would be to swap the CCRM or ECU to see if the fault is fixed with a replacement. It seems you had the same concern two months ago you didn't mention in this thread, and a CCRM didn't fix it.

    1993:
    [​IMG]

    The symptom is not a huge concern, but you should identify the wiring fault. You don't want sparks and arcs. Many cars aren't so clever as to turn off the fuel pump if you don't start the car.
     
    Last edited: Jul 10, 2019
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  7. plumber

    plumber SHO Member

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    Thank you for a great reply. Yes a couple months ago my car just died going down the road. After a lot of great help from this forum I found the FP was ok. I then found a bad wire connector to ccrm. After repair the car still would not start so I replaced ccrm. Still no start so I replaced ecm and the car started and has been running find since the other day when I heard FP not stopping as before. I will try to check further this weekend. I just wonder if the car is starting does everything work as it should after startup? Thanks again for the help. Plumber
     
  8. NoSlo

    NoSlo GoldMember

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    Did you only repair sections of specific wires, connecting them just as they were, or was something switched around? Connecting key power instead of the ECU signal to the fuel pump relay input would cause exactly this.
     
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  9. plumber

    plumber SHO Member

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    Hello. I cut out the main connector for power to ccrm and put a new piece of wire with wire nuts in its place. Plumber
     
  10. NoSlo

    NoSlo GoldMember

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    I can't picture the scenario where this would cause the symptom, but you could ensure all three power sources and 5 power pins are supplied as depicted (this is for 1993 ATX since I don't know what tranny you have):



    [​IMG]

    [​IMG]
     
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  11. plumber

    plumber SHO Member

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    Thank you .I have a manual transmission. As usual nothing is constant with this car. Now for 2 days the FP is shutting off like its suppose to so will keep an ear out for it for now till it acts up again. Plumber
     

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