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Discussion Starter #1
Hello,
I got a p0191 code today(fuel rail pressure sensor circuit performance FPR)
No other codes present.

Checked fuel pressure and following are my readings:

key on, engine not started - 55psi
engine started and running at idle - 35 psi
engine at 2000 rpms - 33 psi
engine at 3000 rpms - 33 psi
engine at 4000 rpms - 32 or 33 and engine runs rough

Shouldn't my pressure be higher at 2,3, and 4 thousand rpm's?
does anyone have specifications for what pressures should be under various conditions?

Any response and/or ideas will be greatly appreciated.

Thanks
 

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Hello smcinrox,

I would like to do this test on my car some time later but I don't know how to do it.
My car is 2000 SE OHV, so it should be similar as yours.

1> Can you post an image showing how & where you tested the fuel pressure on your car?
2> Where did you get the fuel pressure gauge from?

Thank you
 

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Hello,
I got a p0191 code today(fuel rail pressure sensor circuit performance FPR)
No other codes present.

Checked fuel pressure and following are my readings:

key on, engine not started - 55psi
engine started and running at idle - 35 psi
engine at 2000 rpms - 33 psi
engine at 3000 rpms - 33 psi
engine at 4000 rpms - 32 or 33 and engine runs rough

Shouldn't my pressure be higher at 2,3, and 4 thousand rpm's?
does anyone have specifications for what pressures should be under various conditions?

Any response and/or ideas will be greatly appreciated.

Thanks
Pressures should be about the same. The difference between idle and 4k RPM is the duty cycle of the injector(on/off time). I believe running pressure should be roughly 39-40 psi minimum.

P.S. Anyone feel free to correct me. It's been awhile since I had a gauge on my bull.
 

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Pressures should be about the same. The difference between idle and 4k RPM is the duty cycle of the injector(on/off time). I believe running pressure should be roughly 39-40 psi minimum.

P.S. Anyone feel free to correct me. It's been awhile since I had a gauge on my bull.
That is the value on a scan tool. On a manual gauge it has an offset depending on on manifold vacuum. More vacuum less pressure.
 

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That is the value on a scan tool. On a manual gauge it has an offset depending on on manifold vacuum. More vacuum less pressure.
Keep in mind guys that the '00+ Taurus have a returnless fuel system. There is no offset for manifold pressure as their isn't a fuel pressure regulator. Fuel pressure is controlled by the PCM based on the fuel pressure sensor. Pressure after prime/start-up will typically be 35 PSI-ish under light load and can range up to almost 50 PSI under heavier loads.

The P0191 code can be caused by a couple of things. The most likely is that the fuel pressure sensor itself isn't functioning properly. If the PCM isn't getting an accurate reading it can't properly control the pressure. The less likely cause is that the pump is failing and is no longer able to satisfy higher fuel demands. I'd start by replacing the pressure sensor.
 

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The pressures listed are representative of what I have seen. The sensor is a fairly common culprit compared to the pump in low pressure situations but these pressures aren't out of line
 

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Keep in mind guys that the '00+ Taurus have a returnless fuel system. There is no offset for manifold pressure as their isn't a fuel pressure regulator. Fuel pressure is controlled by the PCM based on the fuel pressure sensor. Pressure after prime/start-up will typically be 35 PSI-ish under light load and can range up to almost 50 PSI under heavier loads.

The P0191 code can be caused by a couple of things. The most likely is that the fuel pressure sensor itself isn't functioning properly. If the PCM isn't getting an accurate reading it can't properly control the pressure. The less likely cause is that the pump is failing and is no longer able to satisfy higher fuel demands. I'd start by replacing the pressure sensor.
For what it is worth.
'00 and older had fuel pressure regulator and return line.
'01 one year only fuel pressure regulated inside the filter with return fron the filter to tank. (semi return system)
'02 and later had pressure sensor on fuel rail, adjusted "effective" volts to the pump to manage the pressure.

I think 55 is way to high and anything less than 36 is too low.
Good case for module that regulates the volts to the pump is messed up.


Others chime in.

-chart-
 

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Discussion Starter #10
Keep in mind guys that the '00+ Taurus have a returnless fuel system. There is no offset for manifold pressure as their isn't a fuel pressure regulator. Fuel pressure is controlled by the PCM based on the fuel pressure sensor. Pressure after prime/start-up will typically be 35 PSI-ish under light load and can range up to almost 50 PSI under heavier loads.

The P0191 code can be caused by a couple of things. The most likely is that the fuel pressure sensor itself isn't functioning properly. If the PCM isn't getting an accurate reading it can't properly control the pressure. The less likely cause is that the pump is failing and is no longer able to satisfy higher fuel demands. I'd start by replacing the pressure sensor.
I think I can locate a scan tool that will show real time data. What could I look at that would help me diagnose that the fuel pressure sensor is good or bad. If it was a cheap little sensor I'd just replace it, but the prices I've found are between $80 and $110.

Just an FYI. The entire fuel pump assembly (new assembly) was replaced 10 months ago for an unrelated problem.
 

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Discussion Starter #11
Hello smcinrox,

I would like to do this test on my car some time later but I don't know how to do it.
My car is 2000 SE OHV, so it should be similar as yours.

1> Can you post an image showing how & where you tested the fuel pressure on your car?
2> Where did you get the fuel pressure gauge from?

Thank you
Don't have a picture but there is a shrader valve on the right side of the fuel rail as viewed from front of car with hood open.(Shrader valve looks and operates like a tire stem where you add air) The shrader valve usually has a protective screw on cap that needs to be unscrewed to access the test port. I rented the pressure testing kit at autozone but I would think most other auto parts stores would have it as well.
 

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Keep in mind guys that the '00+ Taurus have a returnless fuel system. There is no offset for manifold pressure as their isn't a fuel pressure regulator. Fuel pressure is controlled by the PCM based on the fuel pressure sensor. Pressure after prime/start-up will typically be 35 PSI-ish under light load and can range up to almost 50 PSI under heavier loads.

The P0191 code can be caused by a couple of things. The most likely is that the fuel pressure sensor itself isn't functioning properly. If the PCM isn't getting an accurate reading it can't properly control the pressure. The less likely cause is that the pump is failing and is no longer able to satisfy higher fuel demands. I'd start by replacing the pressure sensor.
I spent 2 weeks with a manual fuel pressure gauge on my 03 and the pressure did vary depending on manifold vacuum. The fuel pressure sensor on the rail has a vacuum line on it.

Pretty good article in the link.

http://www.underhoodservice.com/Article/40022/under_pressure_maintaining_fordx2019s_electronic_returnless_fuel_system.aspx

I am only directing my comments to the returnless style system not the older stuff as I have not played with it.
 

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For what it is worth.
'00 and older had fuel pressure regulator and return line.
'01 one year only fuel pressure regulated inside the filter with return fron the filter to tank. (semi return system)
'02 and later had pressure sensor on fuel rail, adjusted "effective" volts to the pump to manage the pressure.

I think 55 is way to high and anything less than 36 is too low.
Good case for module that regulates the volts to the pump is messed up.


Others chime in.

-chart-
I'm not sure where this information came from. All Gen 4 Taurus'/Sables have a return-less fuel system. My '00 most certainly does not have a fuel pressure regulator or a return line (I just double checked to make sure I wasn't losing my marbles). I also just checked the Ford schematics. They are indeed all return-less.

Before this thread goes off in a direction it doesn't need to, lets look briefly at how the return-less fuel system works. There is a pressure sensor on the end of the back fuel rail on the passenger side. The feed line from the pump connects to this sensor and feeds the fuel rails through it. The PCM uses the signal from this sensor to determine the current fuel pressure. It sends a signal to the fuel pump driver module, which is behind the back seat, telling it to speed up or slow down the pump to achieve its target fuel pressure. The fuel pump driver module does this by pulsing the pump's ground. Unlike the old return style systems, the fuel pressure is not static. The PCM can and does vary it depending on the fuel delivery needs. At prime/pre-start, it goes to full pressure. This should be about 50-55 PSI. Once the engine starts it reduces the fuel pressure. This is typically in the 35 PSI range. Under a heavy load it may increase the pressure back towards 50 PSI. The fuel pressures listed by the OP are not horribly out of line.

The entire system is monitored for faults by the PCM. The P0191 code indicates that the PCM is either not seeing the fuel pressure it expects, or it is seeing an erratic signal from the fuel pressure sensor. 9 times out of ten this is due to a faulty fuel pressure sensor/wiring. On occasion, it can be due to a faulty fuel pump itself. If you're not having any drive-ability issues there's no reason to suspect the pump being the problem. A fuel pump driver module fault is not likely to cause this code, but trigger one of it's own. The recommended course of action for this code is to replace the fuel pump pressure sensor. I would also inspect the wiring to it first. A short could very well cause this code. Personally, I'd check the wiring then clear the code and wait to see it it comes back before I replaced the sensor.

engine at 4000 rpms - 32 or 33 and engine runs rough
FYI, your engine is most likely running rough here because you're hitting the 4k RPM rev limiter imposed by the PCM when the vehicle is in park.
 

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Discussion Starter #14
Personally, I'd check the wiring then clear the code and wait to see it it comes back before I replaced the sensor.



FYI, your engine is most likely running rough here because you're hitting the 4k RPM rev limiter imposed by the PCM when the vehicle is in park.
Thanks,

Last night I changed the fuel filter for the heck of it. (cheap, easy, and it was time) I took it for a test drive and no hesitation under heavy load while driving. (even above 4 grand on tach.) I cleared the code after checking the wiring (visual check). I'll see if the code comes back.

Thanks for the info on the 4K Rev limiter
 

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I'm not sure where this information came from. All Gen 4 Taurus'/Sables have a return-less fuel system. My '00 most certainly does not have a fuel pressure regulator or a return line (I just double checked to make sure I wasn't losing my marbles). I also just checked the Ford schematics. They are indeed all return-less.

Before this thread goes off in a direction it doesn't need to, lets look briefly at how the return-less fuel system works. There is a pressure sensor on the end of the back fuel rail on the passenger side. The feed line from the pump connects to this sensor and feeds the fuel rails through it. The PCM uses the signal from this sensor to determine the current fuel pressure. It sends a signal to the fuel pump driver module, which is behind the back seat, telling it to speed up or slow down the pump to achieve its target fuel pressure. The fuel pump driver module does this by pulsing the pump's ground. Unlike the old return style systems, the fuel pressure is not static. The PCM can and does vary it depending on the fuel delivery needs. At prime/pre-start, it goes to full pressure. This should be about 50-55 PSI. Once the engine starts it reduces the fuel pressure. This is typically in the 35 PSI range. Under a heavy load it may increase the pressure back towards 50 PSI. The fuel pressures listed by the OP are not horribly out of line.

The entire system is monitored for faults by the PCM. The P0191 code indicates that the PCM is either not seeing the fuel pressure it expects, or it is seeing an erratic signal from the fuel pressure sensor. 9 times out of ten this is due to a faulty fuel pressure sensor/wiring. On occasion, it can be due to a faulty fuel pump itself. If you're not having any drive-ability issues there's no reason to suspect the pump being the problem. A fuel pump driver module fault is not likely to cause this code, but trigger one of it's own. The recommended course of action for this code is to replace the fuel pump pressure sensor. I would also inspect the wiring to it first. A short could very well cause this code. Personally, I'd check the wiring then clear the code and wait to see it it comes back before I replaced the sensor.



FYI, your engine is most likely running rough here because you're hitting the 4k RPM rev limiter imposed by the PCM when the vehicle is in park.
Except for the '01 which has no pressure sensor, and has a pressure regulator in the fuel filter and a short return line to the tank. Filter pic attached. Nothing on the fuel rail at the engine except for the Shrader valve. According to Rockauto, this is a one year only, so it is not like MY '01 is a anomoly.

So, '00 is a one year only for somethings, '01 is one year only for some things, '02 and '03 are the same except for alternator. Maybe!

-chart-
 

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Except for the '01 which has no pressure sensor, and has a pressure regulator in the fuel filter and a short return line to the tank. Filter pic attached. Nothing on the fuel rail at the engine except for the Shrader valve. According to Rockauto, this is a one year only, so it is not like MY '01 is a anomoly.

So, '00 is a one year only for somethings, '01 is one year only for some things, '02 and '03 are the same except for alternator. Maybe!

-chart-
The '01s do indeed have a fuel pressure sensor. The diagram below is for an '01 'Tec, but the Vulcan is similar. The part labeled 9F972 is the fuel pressure sensor. They have a fuel pump driver module as well. It is a PCM controlled returnless fuel system.



Some '01s (built between some time in February '01 and the end of the model year) do have a fuel filter with an internal safety bypass. This only functions to bleed excessive pressure. In normal operation it has no impact on fuel pressure. The '01s fuel system functions just like any other Gen 4.
 

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The '01s do indeed have a fuel pressure sensor. The diagram below is for an '01 'Tec, but the Vulcan is similar. The part labeled 9F972 is the fuel pressure sensor. They have a fuel pump driver module as well. It is a PCM controlled returnless fuel system.



Some '01s (built between some time in February '01 and the end of the model year) do have a fuel filter with an internal safety bypass. This only functions to bleed excessive pressure. In normal operation it has no impact on fuel pressure. The '01s fuel system functions just like any other Gen 4.
If there is a fuel pressure sensor on this engine, I would really like to know where they put it. See pic.

Thanks.

-chart-
 

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If there is a fuel pressure sensor on this engine, I would really like to know where they put it. See pic.

Thanks.

-chart-
Weird. Looking through the databases, I can see a couple of mid-year changes. All of them show a fuel pressure sensor in the wiring diagrams. None of the parts schematics show it being anywhere other than on the rail though. Of course, none of them show the dual inlet filter either. If that's not the sensor upstream from the rail on the fuel line in your picture, I can only assume it's connected to the second port on the fuel filter. There's no way the system could function without it. Even if it had a mechanical return system at the rear, which it can't based on PCM part #'s and the presence of a fuel pump driver module in all '01s, it would need an engine vacuum reference at the regulator. I guess '01 was just a really odd-ball year. Every one I've ever seen had the FPS on the rail and a single in/out fuel filter.
 

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Hey what kinda cool data base do you have for PCM codes and the like?
 

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Weird. Looking through the databases, I can see a couple of mid-year changes. All of them show a fuel pressure sensor in the wiring diagrams. None of the parts schematics show it being anywhere other than on the rail though. Of course, none of them show the dual inlet filter either. If that's not the sensor upstream from the rail on the fuel line in your picture, I can only assume it's connected to the second port on the fuel filter. There's no way the system could function without it. Even if it had a mechanical return system at the rear, which it can't based on PCM part #'s and the presence of a fuel pump driver module in all '01s, it would need an engine vacuum reference at the regulator. I guess '01 was just a really odd-ball year. Every one I've ever seen had the FPS on the rail and a single in/out fuel filter.
My ultragage does not report any fuel pressure on the '01 but does on the '03. When I chanded fuel filters on my 3, the Lin Cont had a shrader valve and pr sensor side by side, my '03 DOHC has only the pr sensor and no shrader valve. The '01 DOHC has only the Srader valve in the same place the '03 has it's pr sensor. Others with '01 might want to chime in.

-chart-
 
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