Found this on another forum page. he calls the Fuel Rail Pressure Transducer Sensor a Fuel Rail Pressure Sensor (FRPS) but it's the same thing.
Okay, so hopefully this will help someone out. I have searched high and low for information regarding fuel rail pressure sensor (FRPS) issues and learned quite a bit actually. Ford has a whole diagnostic procedure for checking the sensor and fuel issues in general, but I can boil it down for you here.
When your car throws a P0193 code (mine is a 2006 V6 4.0L) what this is saying is that the voltage signal return is high from the sensor. Typically the voltage will be between 2-5 volts and this correlates to the pressure seen on the diaphragm of the sensor. The higher the voltage, the higher the pressure on the fuel rails. Since the fuel system is returnless, the PCM tells the fuel pump to slow down delivery of fuel. The result of a high signal is the fuel delivery is reduced and the car may run rough, especially at idle, or not at all.
The usual advice is to replace the FRPS which is around $80. Some people have suggested to check the vacuum line to the sensor for fuel, which indicates a blown diaphragm. This is a good thing to do, since the part is expensive. I have some recommendations here:
Before doing anything and throwing parts and money at it, check your connector at the FRPS. After changing a lot of stuff in the car, I finally traced it to the connector being loose. More on this later.
1. If you have access to a tuner, connect it to the OBD port and look at the Fuel Pressure. Please note that the PID may be reading Fuel Rail Pressure relative to Intake Manifold Pressure. This will give you a reading the is around 10 psi higher than your actual pressure. Fuel pressure in the lines is normally around 30-35 psi at idle. If the PID reads around 40-45, then it should be normal. If the PID reads 75 or so, there is a problem with the sensor and/or circuit.
1.1 If you have an Android phone, get the Torque App and a bluetooth OBD dongle. You can get one from Amazon for like $25. The App can then read most of the PIDs and report back like a tuner can. The app has some cool features and with a car mount for your phone, you can display lots of information and gauges in real time.
2. Change you fuel filter if it hasn't been done in a while. $12-15 dollars.
3. If you suspect that you have a fuel delivery problem, it is highly recommended to get a fuel pressure tester. You can buy one or loan one from Autozone or Advance, etc. Make sure it is a 100 psi unit. Since my particular engine does not have a schrader valve on the fuel rail, I had to tap into a fuel line. There are adapters that you can buy the will tap into the line on the driver's side where the body fuel line meets the engine fuel line.
Fuel Injection Pressure Tester Adapter Low Pressure CFI
This makes it very easy to check the pressure with a gauge. BTW, in my opinion, a fuel pressure gauge (electric) mounted in the vehicle with a returnless system doesn't seem worth it, since the pressure reading will bounce around. My 2 cents if you are thinking of adding a gauge.
4. If you have no fuel delivery (the pump should kick on Key On Engine Off) then it's time to look at fuses and/or the pump itself. In the later model mustangs, the gas tank does not have to drop. There is a access panel under the rear seat. The swap is easy, but again, an expensive fix especially if not necessary.
5. Fuel Pump Driver Module (FPDM). This guy is well known to the F-150 crowd since it goes bad for them often. Mustangs, well not so often. This is a last resort type of replacement. There isn't a good backyard mechanic test for the FPDM that I know of, so think hard before swapping this out. They are around $80 on Amazon and more elsewhere.
6. Tunes. If you have a tune in the car, and it's been running for a while, it is unlikely that the tune is responsible. Either way, restore the car to the stock tune and see if the code clears up. This way you can get back to your tuning company and work with them if it appears to be tune related.
7. FRPS harness connector. Well, after swapping a lot of parts and doing electrical diagnostics, I figured out that the connector was not making a good connection. With the car running, and a fuel pressure gauge hooked up, I could see 32 psi in the line, and 75 psi on the Torque App. I pressed on the connector and the App reported back 40-45 psi, which is normal since it is taking a differential reading. After finding this, I looked online for one of these connectors to replace the pigtail. First thing, they are hard to identify and Ford used the same part number for many different connectors. The one that I believe is correct is $56! No way am I paying that for a connector. I studied the connector and with a very small screwdriver, pushed the blades closer together so they would grab the single blades on the sensor side better. It's similar to a household outlet, just with four cavities in this sensor. The older Mustangs have a three wire sensor.
The car is now running normal and I gave it light tune up, cleaned the MAF sensor and throttle body. Running pretty smooth.
So hopefully my mistakes and lessons can be of use to someone. I know it gets frustrating and throwing parts at a problem is quick and dirty, especially if you HAVE to get the vehicle running (daily driver). Check the connectors first, you'll be surprised that they work themselves loose.
Okay, update...
Shortly after monkeying with the connector for the FPRS, I starting getting the P0193 code again. I hooked up the Bluetooth adapter and I could see the fuel pressure spiking to 75.1 psi now and then, especially when hitting larger bumps.
I finally broke down and bought a new connector from Rock Auto. The other day they posted a forum discount and I remembered from searching around that they actually have the correct connector. Ended up being around $35 and they shipped it pretty fast. I got an Airtex 1P1743 connector which has Ford written on the instructions. Presumably they are an OEM supplier. The connector is high quality and the wires are superb, much better gauge and quality that the original harness wires.
My neighbor and I soldered and shrink tubed the wires together and BAM! The car idles at 39 psi (Fuel pressure relative to manifold pressure). I have not taken it on the road, but I have a good feeling that this is the cure.
