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Fuel Filter Flush - Depressurize

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  • Fuel Filter Flush - Depressurize

    I'm going to flush out the system tomorrow as per the TSB and would like imput as to easiest way to depressurize the low pressure fuel system. I have read about pulling the fuel pump fuse (to disable the tank solinoids) and then running the engine to empty but wonder if this might damage the catalytic convertors ?

    The shop manual requires using the schader valve depressure point on the engine fuel rails as the preferred method but this requires a special kit although I think a standard gasoline version of the kit would work.

    Any input would be appreciated.

    The car is a 2003 Crown Vic P71 dedicated NGV.

  • #2
    Re: Fuel Filter Flush - Depressurize

    Originally posted by p71 View Post
    .. and then running the engine to empty but wonder if this might damage the catalytic convertors?
    Unlikely. Most internal combustion engines that are running correctly, when out of fuel, stop running.



    http://www.catalyticconverter.org/failure/index.htm
    Last edited by jblue; 03-18-2009, 05:50 PM.


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    • #3
      Re: Fuel Filter Flush - Depressurize

      Found out through the Shop Manual and a new TSB that this year car uses the fuse removal method to depressurize the low pressure system. To be 99.99% safe the manual shutoff screws for the tank solenoids should also be closed.

      Thanks for the info and the link to your site.

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      • #4
        Re: Fuel Filter Flush - Depressurize

        I have a 99 vic also and when i de presssurize the system to clean the injectors via the filter bowl i turn the manual shut off valve (red oval knob) that is located right behind the filter bowl and pressure regulator, then I either remove the bolt in the bottom of the filter bowl, venting the system, or run the motor till it dies.

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        • #5
          Re: Fuel Filter Flush - Depressurize

          Pickcng, I see you are new at this by your question. Turn the 1/4 turn valve off first. Next, run the vehicle until it stops running.(this will bring system pressure down to around 100 psi). Only after it stops running (Runs out of fuel) do you start taking apart the filter housing. Oh yes, don't forget to turn off the ignition AFTER the vehicle quits running.

          If the vehicle does not stop running, then you can pull the "fuel pump relay" and this should prevent the tank valves from opening and will do about the same thing as turning off the 1/4 valve. Ford used the "fuel pump relay" in the underhood relay box to control the CNG tank valves since there was no longer a gasoline fuel pump.

          Forgive me if I am a little blunt, but this is a safety issue, and I don't want to see anyone hurt. The order of the operations and the word "or" in the last line of your post raised a red flag with me (you could have start opening a filter housing with 3,000 psi pressure).

          The post previous to your's was correct in using the manual shutoff valve on each tank valve is the safest way, but you can not generally get to the screws in the upper tank valves because of the "vapor box".

          Be safe and take care

          Larrycng
          Last edited by larrycng; 03-24-2009, 06:39 PM.

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          • #6
            Re: Fuel Filter Flush - Depressurize

            I don't have a wiring diagram in front of me so I am not 100% sure. But, I think that pulling the fuel pump relay may also kill the power to the isolation valve. This would stall the engine but leave pressure in the line.

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            • #7
              Re: Fuel Filter Flush - Depressurize

              Karl, I think a have a wiring diagram, I'll find it, check it and let you know

              Thanks

              Larrycng

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              • #8
                Re: Fuel Filter Flush - Depressurize

                Originally posted by karlhafen View Post
                I don't have a wiring diagram in front of me so I am not 100% sure. But, I think that pulling the fuel pump relay may also kill the power to the isolation valve. This would stall the engine but leave pressure in the line.
                Well you made me work.

                According to the '99 crown vic diagram from On-Demand, the load side of the "fuel valve relay" (old fuel pump relay) one leg feeds the inertia switch then in series to the tank valves which are parallel, and the other leg sends a 12 volt signal to pin 40 of the PCM "fuel solenoid vlv". Unless the absence of the 12 volt signal to pin 40 will cause the engine to shut down, then the engine should stay running. I don't know the answer to that one. Trying to remember back, I believe the engine will continue to run.

                The best way determine the answer is to start the engine and pull the relay.

                Also, I thought Ford dropped the 1/4 turn valves in '98 or '99?

                Take Care

                Larrycng

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                • #9
                  Re: Fuel Filter Flush - Depressurize

                  If the wiring diagram I am looking at is to be believed, the fuel pump relay on this car does nothing. It looks like the tank valves and isolation valve are powered directly by the pcm through the inertia switch. Or it could just be that I am just up past my bed time.

                  Thanks
                  Karl
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