Adjustable Fuel Pressure Regulator

Discussion in 'Fox 5.0 Mustang Tech' started by John Dirks Jr, Aug 28, 2013.

  1. have you replaced the fuel filter yet?
  2. Yes. It was done before these symptoms showed up. So we can rule it out.
  3. TFI module and pickup on the distributor could also be culprits. I wouldnt hang up on the fuel system. the regulator rarely fails, and unless there is trash in your tank the pump doesnt slow down flow. If you had fuel pump issues it would die every time it got hot.
  4. How old are the plug, wires, cap and rotor?
  5. Plugs are new. Cap and wires in very good shape.
  6. have you started the surging idle check list? you are grabbing at straws until you actually go through the diagnostic process.
  7. I'm in the diagnostic process. I would not characterize what I'm doing as grabbing at straws. Sure, this is my first fuel injected Mustang but I'm no rookie to diagnosing problems with cars.

    The other suggestions that have been made are valid. However, I've experienced fuel starvation numerous times before. That is what I'm feeling in this case. That is why my diagnosing process is beginning with the fuel system.

    I'll keep this group posted on what I find. Just real busy with multiple obligations absorbing my time.
  8. Not trying to sound condescending. The ecu on these cars is extremely temperamental and the slightest change or ground fault can cause idle and fuel issues.
  9. I didnt go back and read every post again, but did the OP ever go and check his FPR for signs of failure? That would be my first thing to check.

    I recommend attaching a FP gauge and see what happens when he applied the throttle under load. You can buy a rail mounted one fairly cheap.
  10. It's all good. Btw, my idle is fine. No surging.

    I plan to check the regulator for diaphragm failure first. From there, I'll hook a gauge up and look at the readings.
  11. DYI fuel pressure gauge setup...

    Fuel pressure gauge adapter fittings: AN 4 to 1/16” pipe 1/16” male pipe to 1/8” female pipe


    I made my own pressure gauge and holder. I bought the NOS or Autometer adapter that you screw into the place on the fuel line where the schrader valve goes. You have to remove the Schrader valve, but save it, since you will reuse it. I ran a piece of SS (stainless steel) braided hose to a 1/8” pipe brass tee fitting that I mounted on the fender well by the MAF. I made a mount bracket out of aluminum angle I got from Home depot and bolted it to the fender well. Then I mounted the brass tee to it with some machine screws and a plate. I sandwiched the brass tee between the aluminum angle and a flat piece of aluminum that I trimmed off the extra aluminum angle. Three screws laid out in a triangle pattern go through both pieces of aluminum to clamp the tee in place. Put the Schrader valve in the spare port of the brass tee. I used a cheap industrial gauge from MSC Direct ( P/N 56468499). It works great and was cheaper than (less than $8) anything Summit had.

    If you look through the MSC Direct catalog, you can find any type of gauge you want, including liquid filled. You only need a liquid filled gauge if you mount it directly on the engine. The liquid filling dampens out the vibrations.

    You can buy the Autometer Stainless Steel braided hose for like $60. Or a local shop that makes hydraulic hose assemblies can make it for you at a cheaper price. Ordinary low pressure hydraulic hose can be used in place of the Stainless Steel braided hose, the Stainless Steel braided hose just looks nice. I got mine for $4 at a place that sells industrial and military surplus parts of all kinds. The Stainless Steel braided hose goes for about $4+ a foot and the fittings are probably about $6-$10 each. You can make your own and save some $$$, the shops may have a setup or labor charge to fabricate the hose assembly.

    [ FPGauge9.jpg FPGauge5.jpg

    Safety device to prevent major fuel loss in the event of a failure of the hose, fittings or gauge...
    stykthyn likes this.
  12. that is some pimp DIY action right there.
  13. The regulator diaphragm is holding a vacuum so I guess its not ruptured. I plan to pick of a pressure gauge this afternoon. I'll post what I find.
  14. I picked up a pressure gauge and followed the instructions that came with it.

    On the key on/off cycle test (engine not running) I had to cycle at least 10 times and could barely get it up to 20psi. It basically drops to zero in one second as soon as I turn the key off.

    On the engine run test, I got 28psi at idle with vacuum line connected to regulator. No difference in pressure with vacuum line removed.

    So, I guess this means its time for a new fuel pump. What say you? If I need a pump, which one would you recommend?

    Here's running pressure at idle (same reading with vacuum line connected or not.

  15. 155 or 190. You do not want to get a pump that pushes too much for your application.
  16. A 110 is more than enough for a mild Fox build
  17. On the fuel pump rating, are the numbers you are discussing LPH or GPH?

    And since I'm new to the fuel injected Fox Mustang, can you confirm that the pressure results I posted indicate a failing fuel pump?
  18. i would say yes a failing pump or a totally clogged fuel flter or pump screen