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Need help with fuel pressure test

Discussion in '1994-2004 V6 Mustang Tech' started by Ivan Henthorne, Jun 1, 2019.

  1. Ivan Henthorne

    Ivan Henthorne New Member

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    Hi All, new to the forum, but not to working on cars.

    I have a 2004 Anniversary Edition 3.8L 5spd, and I'm having some trouble with it. I wanted to test fuel pressure, because the car is bogging down when taking off from a stop. You literally have to just push the gas and pray it doesn't stall out before it begins to accelerate. I rented a tester thinking I could at least rule out the pump and filter instead of just throwing parts at it, but instead of having a fuel pressure test valve, there is only a Fuel rail pressure switch. I thought maybe underneath it would be a valve to connect the fuel pressure gauge, but it's just a smooth hole with no valve or threads.

    I'm wondering if there is a separate adapter I need to find or a different place to measure the pressure manually. Or maybe someone has had a similar issue with their car, and knows something better to start with.

    I have recently replaced the plugs and wires, air filter, belts and hoses for maintenance, but this problem is getting worse. I also had to replace the linkage rod bushings for the IMRC. Maybe it's stuck closed, but how do I tell? I don't have a scan tool. I bought a USB cable to connect to the OBDII connector, but haven't found any affordable SW to use it with. The seller screwed me over and never sent the code for the SW.

    Anyway, enough rambling. Thanks in advance!
     
  2. 08'MustangDude

    08'MustangDude Profile Violation

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  3. Ivan Henthorne

    Ivan Henthorne New Member

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    Thanks for the reply MustangDude.

    I found that thread too, but he never says where it is. I messaged him, but no reply yet. Not holding my breath, as his last time on the forum was 2013.

    I know everyone says it’s supposed to be on the front of the rail on the driver side, but mine has a Fuel Rail Pressure Switch located there, not a Schraeder valve. I’m wondering if there is an adapter that is fitted between the switch and the rail that has a connection for the manual pressure gauge or something.

    If not how could you check it manually? All the lines are hard plastic with fuel line fittings. No rubber or hose clamps to put the tester in-line.

    I guess Ford just expects us to trust the switch will never fail?
     
  4. 08'MustangDude

    08'MustangDude Profile Violation

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    Looks like it's facing downward on an angle, under the intake manifold
    on the driver side underneath the fuel pressure sensor.
    [​IMG]
     
  5. Pete fender

    Pete fender Pete Fender

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    Hey...
    New member, same problem.
    I am using a pressure tester on the Schraeder valve, 0 psi.
    When it gets cooler, I am dropping the tank and installing the new pump assembly.
    I had put a new pump motor in last year, but these assemblies have a regulator, of a sort, built into the bucket it all sits in. It is better to replace the entire assembly.
    The hoses in the tank are plastic, and eventually develop leaks.
    Also, the pump has a "Fuel Pump Driver Module" in the trunk, on the driver's rear wheel well, inside the trunk.
    The driver, the fuel rail pressure sensor, mass air, and the PCM control the speed of the pump motor, in relationship to throttle angle, as this is a return-less fuel injection system.
     
  6. Pete fender

    Pete fender Pete Fender

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    That is the Fuel Rail Pressure Sensor, the Schraeder valve is under that, pointing almost horizontally.
     
    Last edited: Jun 4, 2019
  7. Ivan Henthorne

    Ivan Henthorne New Member

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    I saw that video on you tube as well, but couldn't tell what he had it connected to. There’s nothing there on my car. As far as I know the car is stock, so I’m not sure why this doesn't match what else is out there. This image is the bottom of the left front corner of the fuel rail, right under the fuel pressure sensor. That 90 elbow is me trying to find the right spot to take the video.

    I really do appreciate the time you've taken to help me out. That cylindrical thing behind the elbow is a funnel i forgot to move out of the way before I took the video. :coolface:

    It just dawned on me, I think this person is using the adapter I'm wondering about.





    fuel pressure rail.png
     
    Last edited: Jun 5, 2019
  8. 08'MustangDude

    08'MustangDude Profile Violation

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    Don't know man, everyone says the valve is on the fuel rail...
     
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  9. billegoat

    billegoat Member

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    My 04 3.9 doesn't have it either ...
     
    Ivan Henthorne likes this.
  10. Pete fender

    Pete fender Pete Fender

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    Yes, that is where it's supposed to be.
    Right where the brass looking fitting is,his knuckle is pointing directly at it, not his finger.
    It's possible your fuel rail came from, or was made for a front wheel drive motor?
    If you can't find the valve, you may have to check the rail pressure by using an AC can tap for R-22, I have seen it done on Diesel trucks before.
    They run a lot more pressure, and so does AC.
    It's called a bullitt piercing valve, ask for the one for R-22, 134a is too big.
    Here is a how to...

     
  11. Pete fender

    Pete fender Pete Fender

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    Last edited: Jun 8, 2019
  12. Pete fender

    Pete fender Pete Fender

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  13. Ivan Henthorne

    Ivan Henthorne New Member

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  14. Pete fender

    Pete fender Pete Fender

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    I installed the new assembly, the car is now fixed.
    My pressure gauge was reading zero, so I turned the piece that pushes the Schraeder valve out 2 turns.
    It was not pushing the valve in.
     
  15. Pete fender

    Pete fender Pete Fender

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    Here is a bottom view of the fuel rail. the valve is at the top left of the picture, you can see the valve cap sticking up.
    The FRPS has been removed.
     

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    Last edited: Jun 9, 2019
  16. Ivan Henthorne

    Ivan Henthorne New Member

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    So, here’s an update, because I hate it when people ask for help and don’t tell you what happened in the end.

    I replaced the fuel pump and filter assembly, no change. Meh, it was 15 years old, so no skin off my nose.

    Next I pulled the plenum, cleaned the IMRC valves and intake ports and replaced the fuel rail with a used one from the salvage yard, no change. Oh well, the fuel rail was $7 at a upullit yard and I used $7 worth of injector cleaner to clean everything up, which it really needed, btw.
    (And $20 for the oil change)


    Last thing I did was to replace the fuel control module, or CCRM. FINALLY a CHANGE!! Now the car no longer bogs down when accelerating through a turn or trying to cut acrosstraffic or take off from a stop.

    I guess the old module maybe wasn’t opening the IMRC valves, because after this I also had no pre-ignition rattle from the engine at higher RPMs.

    Thanks everyone for your input and suggestions. I know this is probably just luck, but sometimes it’s better to be lucky than good.

    Have a good one!!
     
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