Fuel Rail Pressure Sensor

[imp]

2004 Explorer 4.0L. 2 years ago, I got a P0193 code, "Fuel Rail Pressure Sensor Circuit High Input". At the time, knowing I have the returnless fuel system, this thing's gotta tell the PCM the fuel pressure, and PCM controls Fuel Pump speed to maintain pressure within tight limits, around 60psi. I figured if that sensor "buys it", the vehicle has no fuel supply.

Anyone know if that's true? I replaced it with a new one from NAPA, CEL gone, ran fine 2 years, now getting same code again. About 20,000 miles. I"ve been erasing the code, it's coming back now sporadically. This morning wife & I left for doctor visit 80 mile round trip, no CEL. I bought another new sensor, but kinda hoped for cooler weather before laying under the hood; it's gettin' kinda hard doing this **** at 71! Plus, it's been 110+` degrees every day for 6 weeks.

I'd feel lots better knowing Ford has programmed in some kind of "limp" strategy for failed fuel pressure sensor, like, it runs pump at some intermittent interval they found could get you by without busting a fuel line from too high pressure, or maybe a pressure relief valve at the pump output which dumped back into tank at maybe 70psi.

Any ideas or definite knowledge of effect of loss of fuel pressure sensor?

Thanks for reading! imp

 

[obie]

SOHC engine, right? Yes, it has a fuel pressure relief valve. I can't link directly to the Ford manuals, but this is good enough: http://www.autozone.com/autozone/re...epairGuideContent.jsp?pageId=0996b43f802e3ddb

I looked through all the system info and troubleshooting and diagnostics sections but couldn't find an exact number on what the valve opens at. But the PCM is programmed to go into limp mode after any kind of serious sensor failure, so I assume that fuel system would be a very high priority for it.

 

[imp]

SOHC engine, right? Yes, it has a fuel pressure relief valve. I can't link directly to the Ford manuals, but this is good enough: http://www.autozone.com/autozone/re...epairGuideContent.jsp?pageId=0996b43f802e3ddb

I looked through all the system info and troubleshooting and diagnostics sections but couldn't find an exact number on what the valve opens at. But the PCM is programmed to go into limp mode after any kind of serious sensor failure, so I assume that fuel system would be a very high priority for it.

Thank you kindly for responding! Just a few moments ago, a post indicated that a failed fuel pump "threw" the P01893 Fuel Rail Pressure Sensor code. There seemed to be an open circuit to the pump, which PCM interpreted as "high output", which could mean high resistance looking into the pump from the pressure sensor. I would have thought PCM "looks at" pressure sensor data; this seems misleading. I am lost. imp

 

[rmcknight]

high fuel pressure does not adjust the pump, it has its own pressure regulator built in.
my 2004 v8 runs on lpg thus uses no petrol and got that code (until fixed by a little black box).

In any case, no fuel ever leaked from anywhere, so something stopped the pump from pumping. the pump still operates as it still runs if i hit a button to switch it back to petrol.

 

[imp]

high fuel pressure does not adjust the pump, it has its own pressure regulator built in.
my 2004 v8 runs on lpg thus uses no petrol and got that code (until fixed by a little black box).

In any case, no fuel ever leaked from anywhere, so something stopped the pump from pumping. the pump still operates as it still runs if i hit a button to switch it back to petrol.

As I understand the "returnless" fuel system, and logically, to maintain constant fuel pressure at the fuel rail (and therefore the injectors), the speed of the fuel pump must be controlled in order to feed just the amount of fuel being used at any given moment. Thus, demand for more power drops pressure at the rail, is instantly recognized by the PCM, and it increases pump speed a bit to bring pressure back to normal level. This process is happening continually and very quickly whenever the engine is running. Complicated, but the pumps last FAR longer since they are not continuously putting out their maximum volume as they were with the "return line" (old) system. Old system used a mechanical pressure regulator mounted on the fuel rail which "dumped" the correct amount of fuel back to the tank, to maintain constant pressure.

As a side note, the old system, with say a 100 liter per hour pump, circulated all the fuel out of the tank and back again pretty quickly. This meant any **** stirred up in the tank found it's way to the filter very quickly. The returnless systems now use smaller filters (the ones I've seen, anyway). imp

 

[rmcknight]

i still think the pressure control is calculated by the pump, and the sensor on the rail is independent and just throws codes if not within a range. In other words, the pump has its own way of knowing what the pressure is.

 

[2000StreetRod]

fuel pump driver module?

I'm very interested in this discussion since I have a Stealth 340 fuel pump that dumps most of its fuel directly into the tank via the intank mechanical fuel pressure regulator.

I've learned that the 3rd generation Explorers (your 2004) have a fuel pressure sensor that reports pressure readings to some device.

The 2007-10 Ford Explorer Sport Trac has the same fuel pressure sensor and a Fuel Pump Driver Module (FPDM).

I suspect this is a pulse width modulator (PWM) that controls the pump speed and would like a similar system in my 2nd generation Sport. My Stealth pump is a turbine type that is very compatible with PWM controllers. I can't find an equivalent FPDM for the Explorer in Rock Auto listings. However, according to the following thread it's located under right rear trim panel:2004 No Start, No Fuel w/ P0191 and P0193 Codes

As you point out, imp, the pump should last longer if its not always running at maximum capacity. Also, according to the specifications, mine draws 16 amps at 340 lph.

I've read that the 2nd generation returnless systems are less responsive to engine demand changes than the older return type fuel system because there is no anticipation of engine load changes. The return type fuel pressure regulator "sensed" the change in engine load via the manifold vacuum hose.

It certainly would be nice if I only needed to add a fuel pressure sensor and a FPDM to have a functional upgraded fuel system. Since there are DTCs associated with the fuel pressure sensor the PCM monitors its output. However, the PCM may not interface with the FPDM.

EDIT: According to the following thread the PCM controls the FPDM: Fuel Delivery Issues ***SOLVED*** . But I hope to get a copy of the 2004 wiring diagram to confirm.

EDIT2: According to Advance Auto Dorman FPDM Part No. 601-005 fits a 2004 Explorer but AutoZone says it doesn't fit.

 

[imp]

I'm very interested in this discussion since I have a Stealth 340 fuel pump that dumps most of its fuel directly into the tank via the intank mechanical fuel pressure regulator.

I've learned that the 3rd generation Explorers (your 2004) have a fuel pressure sensor that reports pressure readings to some device.
View attachment 74678

The 2007-10 Ford Explorer Sport Trac has the same fuel pressure sensor and a Fuel Pump Driver Module (FPDM).
View attachment 74677

I suspect this is a pulse width modulator (PWM) that controls the pump speed and would like a similar system in my 2nd generation Sport. My Stealth pump is a turbine type that is very compatible with PWM controllers. I can't find an equivalent FPDM for the Explorer in Rock Auto listings. However, according to the following thread it's located under right rear trim panel:2004 No Start, No Fuel w/ P0191 and P0193 Codes

As you point out, imp, the pump should last longer if its not always running at maximum capacity. Also, according to the specifications, mine draws 16 amps at 340 lph.

I've read that the 2nd generation returnless systems are less responsive to engine demand changes than the older return type fuel system because there is no anticipation of engine load changes. The return type fuel pressure regulator "sensed" the change in engine load via the manifold vacuum hose.

It certainly would be nice if I only needed to add a fuel pressure sensor and a FPDM to have a functional upgraded fuel system. Since there are DTCs associated with the fuel pressure sensor the PCM monitors its output. However, the PCM may not interface with the FPDM.

EDIT: According to the following thread the PCM controls the FPDM: Fuel Delivery Issues ***SOLVED*** . But I hope to get a copy of the 2004 wiring diagram to confirm.

EDIT2: According to Advance Auto Dorman FPDM Part No. 601-005 fits a 2004 Explorer but AutoZone says it doesn't fit.
View attachment 74679
View attachment 74680

I have the 2004 Ford Wiring Diagrams book in front of me. Page 23-4 is the 4.0L diagram showing the FPDM, which is controlled by the PCM. I haven't gone further yet, everthing's continued on other pages, instead of the old huge drawings Helm used to supply. I can scan the needed pages and try to post them, if you need them. Mailing them would be a lot easier, for me. Let me know,

As I suspected the output of the Fuel Rail Pressure Sensor obviously feeds to the PCM. PCM then sends it's control commands to the FPDM. They could not possible have fit the control package in the PCM, without making it a lot bigger. Your talking here control of a lot of power, with a stock pump maybe about 60 or 70 watts.

You seem to know what you're talking about! Refreshing! imp

Edit: Your pic of the pressure sensor at top is correct. Your truck is 2000? You then have return type system, right?

 

[imp]

i still think the pressure control is calculated by the pump, and the sensor on the rail is independent and just throws codes if not within a range. In other words, the pump has its own way of knowing what the pressure is.

The Fuel Rail Pressure and Temperature Sensor pictured in the thread is the right part. It produces a variable output voltage based on the fuel pressure, and sends that data to PCM, which in turn sends it's own control data to the Fuel Pump Driver Module, which has a cable going to the pump itself. The FPDM controls the pump's speed, at the correct level to maintain the desired fuel pressure, regardless of engine speed or load. I have the Ford wiring diagrams to confirm this. imp

 

[2000StreetRod]

fuel pressure control

The PCM probably had an unused analog input and output to monitor the fuel pressure and control the FPDM. The Ford strategy could use the throttle position sensor output to anticipate engine load increase and up the fuel pressure in a manner similar to the rail mounted fuel pressure regulator.

Ford implemented the returnless fuel pressure system in 1999 and that is what I have in my Sport.

Where does the fuel pressure sensor mount? Is on the fuel rail? Does it take the place of the fuel pressure damper? If so, I'll purchase one and experiment with it. I can use the output as a control voltage for a standard PWM DC motor controller. I would just have to scale the voltage for the desired fuel pressure using my Stealth pump and in tank fuel pressure regulator.

 

[imp]

The PCM probably had an unused analog input and output to monitor the fuel pressure and control the FPDM. The Ford strategy could use the throttle position sensor output to anticipate engine load increase and up the fuel pressure in a manner similar to the rail mounted fuel pressure regulator.

Ford implemented the returnless fuel pressure system in 1999 and that is what I have in my Sport.

Where does the fuel pressure sensor mount? Is on the fuel rail? Does it take the place of the fuel pressure damper? If so, I'll purchase one and experiment with it. I can use the output as a control voltage for a standard PWM DC motor controller. I would just have to scale the voltage for the desired fuel pressure using my Stealth pump and in tank fuel pressure regulator.

Mounts directly on the rail assembly, underneath the upper intake manifold; have to remove that to access sensor. The damper I am not familiar with, like an accumulator? You do not mean the return-type system pressure regulator?

I'm impressed with how deeply you are willing to get into this! Bear in mind the pressure sensor measures fuel temperature also. Thus your PCM wants to see that info as well, since fuel density varies with temperature, this making the "mix" complicated. I had a '99 XLS, I was sure it had return type system, but could be wrong; I never got into that one very deeply. I worked extensively with EEC-IV converting from carbs. to EFI 15 years ago; I know IV from top to bottom.

Wondering if you want Ford wiring diagrams, take me up on my offer if you do. I'm retired with nothing to do at the moment! You need the "pin-out" info for your PCM. imp

Edit: I lost you a bit. If your Sport has returnless, what happened to the pressure regulator? Did they use some other means of maintaining pressure constant before the type my '04 has?

 

[2000StreetRod]

regulator in tank

On my returnless system the fuel pressure regulator is mounted in the fuel tank. The bypassed fuel never leaves the tank. This is my fuel pump assembly with the Stealth 340 pump installed.

My fuel pressure damper is mounted on the fuel rail. Looks almost the same as the older fuel pressure regulator except there is no bypass (return) port.

It looks like there is a probe on your fuel pressure sensor which is probably what measures the temperature. It may mount directly into my fuel rail.

 

[FordFool2]

After troubleshooting my sensor, driver module (FPDM), and replacing the pump unit itself, here is one of the better write-ups I came across on how it works:

http://www.explorerforum.com/forums/showthread.php?t=262151

According to the Ford 2004 OBD System Operation Summary:

There is a fuel rail pressure sensor that is tested by the PCM. P0191 is set when demand minus actual is greater than 40 psi.

"Electronic Returnless Fuel Systems (ERFS) utilize a Fuel Pump Driver Module (FPDM) to control fuel pressure.
The PCM uses a Fuel Rail Pressure Sensor (FRP) for feedback. The PCM outputs a duty cycle to the FPDM to
maintain the desired fuel rail pressure. During normal operation, the PCM will output a FP duty cycle from 5% to
51%. The FPDM will run the fuel pump at twice this duty cycle, e.g. if the PCM outputs a 42% duty cycle, the
FPDM will run the fuel pump at 84%. If the PCM outputs a 75% duty cycle, the FPDM will turn off the fuel pump.
The FPDM returns a duty cycled diagnostic signal back to the PCM on the Fuel Pump Monitor (FPM) circuit to
indicate if there are any faults in the FPDM.
If the FPDM does not out any diagnostic signal, (0 or 100% duty cycle), the PCM sets a P1233 DTC. This DTC is
set if the FPDM loses power. This can also occur if the Inertia Fuel Switch is tripped."

Its not the inertia fuel switch or you wouldn't ever get fuel pressure to start. I suspect either the fuel rail pressure sensor or the Fuel Pump Driver Module. I still suggest testing the fuel pressure if there is a test port.

 

[2000StreetRod]

looks promising

I found a photo of a fuel pressure sensor on Rock Auto from a different angle.

It looks like it may bolt up to my stock fuel rail.

Or even to my new Banshee fuel rail.

I assume the top port is a vacuum connection and there is a diaphragm to provide dampening.

Thanks for offering to provide me wiring diagrams. Since the sensor outputs go to the PCM (which I won't be doing) the only thing I need to know is which pins/wire colors are for pressure and the supply voltage provided by the PCM. I'll PM you my email address so you can send me the engine control page showing the sensor as an attachment.

I'll try to purchase a used sensor with mating connector and pigtails. My stock fuel pressure was 62 psi but with the Stealth pump it has increased to 67 psi which will richen my AFR when the PCM is in open loop. After installing the fuel pressure sensor I'll bleed the pressure down to 62 psi and measure the sensor output voltage.

I'd also like the wiring diagram showing the connections to the FPDM. The photo shows more pins on the connector than I expected. I expected two pins for power in from the inertia fuel shutoff, two pins for power out to the fuel pump and two pins for the motor speed control from the PCM. Maybe to save wire routing Ford ran the fuel tank pressure sensor wires and the fuel level sender wires thru the FPDM. If I used the Ford FPDM would only use the power input, output and control lines. I would have to determine the control voltage that results in 62 psi and then match that with the 62 psi sensor output voltage. The Ford FPDM may not have the capacity (215 watts) to control my Stealth pump at max flow rate. However, I have no need for the max flow since it supports 700 bhp.

I am also retired but only 67 years old. I enjoy working on automotive projects especially those involving electronics.

 

[2000StreetRod]

poor memory

After troubleshooting my sensor, driver module (FPDM), and replacing the pump unit itself, here is one of the better write-ups I came across on how it works:

http://www.explorerforum.com/forums/showthread.php?t=262151 . . .

Well, I'm embarrassed to admit that I'm the one that posted that but forgot it. I guess that's an excellent example of me having a senior moment.

That's the same method the PCM uses to control the EGR vacuum regulator and a little more difficult for me to implement than just an analog control voltage.

 

[2000StreetRod]

fuel pressure sensor location

I found a good drawing on AutoZone's website showing the location of the fuel pressure sensor on the 2005 thru 2007 models.

If anyone happens to have the mating 4 pin connector with pigtails or a functional sensor to sell please contact me.

 

[2000StreetRod]

fuel pressure sensor failure

Steve, getting back to the question in your first post, I suspect that if the output of the fuel pressure sensor is so low or so high to result in the duty cycle sent to the FPDM to be greater than 51% or less than 5% the PCM declares the sensor invalid. I have an old copy of the proprietary Ford strategy source code. Typically there is a value stored in a table for an upper and lower limit. It would seem logical to me that the sensor output would be evaluated to be within limits (like it does for other sensors) than evaluating the commanded duty cycle output. I'll search thru the code (more than 8,000 pages) to see if I can find more information. The code may be too old to support the fuel pressure sensor. It would be easy to establish a default commanded duty cycle in the event of a failed pressure sensor but that would change the control from closed to open loop and might be a safey hazard. If the default duty cycle were too high the supply could exceed the demand for varying engine load conditions. It wouldn't be a problem if there is a mechanical fuel pressure regulator in the fuel pump assembly. I'll do a search for a 3rd generation fuel pump assembly photo.

Edit: I found the photo below of a 2004 Explorer fuel pump assembly. The corrugated hose that curves from upward to downward is the bypass hose from the intank fuel pressure regulator.

 

[2000StreetRod]

intial findings

According to Ford the reason for switching to a returnless fuel system was to eliminate returning hot fuel into the tank thus reducing fuel vapor and consumption.

The fuel pump driver module has a way of reporting its status to the PCM. My cursory review of the code indicates that when the fuel pressure rail sensor is determined to have failed the FPDM is commanded to a fixed duty cycle and checked to see if it responds correctly to the command. If so, it appears the PCM depends on the intank fuel pressure regulator to control the pressure.

 

[2000StreetRod]

normal fuel pressure

I found a quote posted on the internet from the 2004 Explorer/Mountaineer Workshop Manual stating that the normal fuel pressure with the ignition on and the engine running or not running is 30 to 40 psi.

 

[2000StreetRod]

Bosch data sheet

The Bosch part number for the fuel pressure/temperature sensor I purchased is 0 261 230 093. The Ford part number is 3F2E-9G756-AD. Curiously, when I entered the Ford P/N into Tasca Ford's database it showed the sensor is for a 2005 thru 2007 Ford Escape and not for the Explorer. I found the Bosch data sheet:
View attachment DiffPressure100_0261230093.pdf
Surprisingly, contrary to what I've read on the internet, the only output from the sensor is temperature compensated relative fuel pressure. The air port is used as a pressure reference even though it is connected to vacuum which varies significantly with engine load. Here's a link to a fuel pressure regulator kit that uses the same sensor: Fuel Pump Controller

Edit: The Ford P/N for the 2004 thru 2009 Explorer sensor is 3F2Z-9G756-AC.

Correction: The fuel pump controller article states that pin 3 of the sensor is the fuel temperature signal. According to the data sheet the pins are misnumbered in the fuel pump article. Pin 2 is the NTC signal and pin 3 is to be connected to VCC (+5 vdc). So there is a temperature and a pressure signal generated by the sensor.