High Fuel Rail Pressure

[FarrukhAnwar]

I have a 2006 Ford Mustang V6 with 200k miles.

When idling, there is a strong fuel smell outside the vehicle (no smell inside though). Engine sometimes idles roughly (RPMs dip and rise) and may stall. When engine is idling rough, exhaust occasionally emits liquid (appears to be fuel) and the car throws codes P0193, P2196, and P2198. The car also sometimes throws code P0463 randomly when idling or driving and the fuel gauge stops working, although this may be unrelated.

Recurring engine trouble codes descriptions:
P0193 – Fuel Rail Pressure Sensor Circuit High
P2196 – O2 Sensor Signal Stuck Rich (Bank 1 Sensor 1)
P2198 – O2 Sensor Signal Stuck Rich (Bank 2 Sensor 1)
P0463 – Fuel Level Sensor Circuit High

After these problems and codes started, I checked the live data and when the car initially starts, the Fuel Rail Pressure Sensor reading starts at 40 PSI (which I researched was normal) before slowly climbing up to 60 PSI after a few minutes, however the fuel pump duty cycle stays at around 25%. So, I decided to put in a new Fuel Rail Pressure Sensor and Fuel Pump Driver Module, but now the Fuel Rail Pressure Sensor reading is always at around 70 PSI when idling or off throttle, with dips in the 50s when doing wide open throttle (complete CSV data attached with graph for fuel rail pressure). Additionally, The Long Term Fuel Trims are very negative (-10% at bank 1 and -15% at bank 2), so I suspect that fuel rail pressure might genuinely be high because of the rich codes, strong fuel smell, and negative fuel trims. I am thinking it could be a bad Fuel Pump, but it could also be bad wiring around the Fuel Pump Driver Module and the Fuel Pump. Also, this may be unrelated, but my scanner reports 16V for the OBD Module Voltage, but my multimeter at the battery confirms a steady 14V. The car is also on an 87 tune, but it hasn't given any problems for a while before this.

Any guidance for further testing or for a fix would be greatly appreciated and thanks for your time in advance!

 

[86GT351]

Did you use Ford OEM parts or aftermarket?

 

[FarrukhAnwar]

Did you use Ford OEM parts or aftermarket?

Aftermarket.

 

[86GT351]

Aftermarket.

That could be the issue. I work at a dealer in service and we see that often. Part just replaced with aftermarket and still has an issue. Replace with OEM and issue solved

 

[FarrukhAnwar]

If I were to try physically testing the fuel rail pressure with a separate gauge, do you know how I would go about doing that?

 

[Eman]

You have to purchase an adapter that goes inline of the fuel line, I believe S&G Tool Aid sells one. Might be # 57260 adapter

 

[FarrukhAnwar]

So, I did some more testing, and it looks like all of the original parts and wiring were working correctly. For some reason, when the car is cold started the fuel rail pressure and fuel pump duty cycle start at 40 PSI and 14% respectively (which I believe is normal), but after idling for a while, they slowly start climbing to 60 PSI and 21%. Does anyone have any idea why the PCM is increasing the fuel pump duty cycle even though the fuel rail pressure should be 40 PSI? I don't think it has to do with a lean condition because the LTFTs are at -10% and -15%.

 

[Eman]

What after market parts are on the car? That's usually the thing that causes the problems. Cold air intake and TB spacers and all of the rest of the stuff causes lean readings. I had lean readings when I bought my 99, removed the aftermarket parts and car runs perfectly.

 

[FarrukhAnwar]

I believe it has an S&B cold air intake, catalytic converter deletes, and Screamin' Demon coil pack and spark plugs done by the previous owner. By the way, I believe the negative fuel trims and high fuel pressure indicate that the car is running rich and I can smell the gasoline smell getting stronger outside the car as the fuel rail pressure increases, and sometimes the exhaust spits out gas. I tried both the stock tune and performance tune and the problem still remains.

 

[Eman]

Take a physical fuel pressure reading

 

[Pentalab]

My 2010 GT....( 4.6L V8) .....with key on, eng OFF, has 50 psi on the fuel rail pressure. With eng on idle it stays at 40 psi. it's stays on 40 psi, even at 6 k rpm, and roush blower with full boost. Fuel rail pressure doesn't budge. FPDC is 40% at idle. 80% at 6 krpm and max boost.

I suspect your fuel pump. Anything > 40 psi is not good.

 

[FarrukhAnwar]

I believe the fuel pump is fine because I put a new one in and the same problem was happening. I will be getting a fuel pressure gauge soon though for more testing. I also forgot to mention that the duty cycle values I mentioned are what the PCM are sending to the FPDM, which is actually half of the value that the fuel pump actually receives, so 14% duty cycle is 28% duty cycle at the pump, and 21% duty cycle is 42% duty cycle at the pump.

For the time being though, it seems to me that something is causing the PCM to increase the fuel pump duty cycle from 14% to 21% as the engine warms up, which in turn increases the fuel pressure. One interesting explanation I saw online was that if the PCM thinks the fuel temperature is getting too high, it will increase the pressure to prevent air bubbles from forming.

Unfortunately, my scanner profile doesn't show fuel rail temperature even though a temperature sensor is built into the FRPS. It would be great if anyone could provide me with the PID and formula to check this, and even better if there is a list of all specific PIDs and formulas for this car. I physically backprobed the sensor to check the temperature voltage and it looked like it was working, but I want to know what the PCM is seeing.

 

[Pentalab]

I believe the fuel pump is fine because I put a new one in and the same problem was happening. I will be getting a fuel pressure gauge soon though for more testing. I also forgot to mention that the duty cycle values I mentioned are what the PCM are sending to the FPDM, which is actually half of the value that the fuel pump actually receives, so 14% duty cycle is 28% duty cycle at the pump, and 21% duty cycle is 42% duty cycle at the pump.

For the time being though, it seems to me that something is causing the PCM to increase the fuel pump duty cycle from 14% to 21% as the engine warms up, which in turn increases the fuel pressure. One interesting explanation I saw online was that if the PCM thinks the fuel temperature is getting too high, it will increase the pressure to prevent air bubbles from forming.

Unfortunately, my scanner profile doesn't show fuel rail temperature even though a temperature sensor is built into the FRPS. It would be great if anyone could provide me with the PID and formula to check this, and even better if there is a list of all specific PIDs and formulas for this car. I physically backprobed the sensor to check the temperature voltage and it looked like it was working, but I want to know what the PCM is seeing.

ur correct. The indicated FPDC on my aeroforce gauges is exactly 1/2 of what it actually is.

A fuel pressure gauge, once u got it installed, will tell you more. You could always use a digital point and shoot IR handheld thermometer to measure the fuel line outer surface temp, and ditto with fuel rails and anything else fuel related.

 

[FarrukhAnwar]

So, I was able to get a bit more data and it looks like as the car warms up, the PCM increases the desired fuel rail pressure from 40 PSI to 60 PSI over time, which increases the fuel pump duty cycle, which increases the actual fuel rail pressure according to the desired pressure. I also checked that the PCM reading of the fuel rail temperature sensor voltage matches the actual voltage found by backprobing. I'll try to hook up a fuel pressure gauge just to double check that the FRPS is reporting the right fuel pressure as well, but from what it looks like to me, all of the physical components are working properly, including the FRPS, FPDM, and the fuel pump, but the PCM is asking for higher fuel rail pressure for some reason. A fuel rail temperature of 120 degrees doesn't seem too hot, so I don't think it's increasing fuel pressure to prevent vapors from forming, but I could be wrong on that. If anyone has any pointers on what to do next, I'd really appreciate it.


Key On Engine Off:



Idling after about 10 minutes:

 

[FarrukhAnwar]

I hooked up a physical fuel pressure gauge, and it confirms that the FRPS is working properly. I really don't know what else to do from here.

 

[chadzrtaylor]

I have a 2006 Ford Mustang V6 with 200k miles.

When idling, there is a strong fuel smell outside the vehicle (no smell inside though). Engine sometimes idles roughly (RPMs dip and rise) and may stall. When engine is idling rough, exhaust occasionally emits liquid (appears to be fuel) and the car throws codes P0193, P2196, and P2198. The car also sometimes throws code P0463 randomly when idling or driving and the fuel gauge stops working, although this may be unrelated.

Recurring engine trouble codes descriptions:
P0193 – Fuel Rail Pressure Sensor Circuit High
P2196 – O2 Sensor Signal Stuck Rich (Bank 1 Sensor 1)
P2198 – O2 Sensor Signal Stuck Rich (Bank 2 Sensor 1)
P0463 – Fuel Level Sensor Circuit High

After these problems and codes started, I checked the live data and when the car initially starts, the Fuel Rail Pressure Sensor reading starts at 40 PSI (which I researched was normal) before slowly climbing up to 60 PSI after a few minutes, however the fuel pump duty cycle stays at around 25%. So, I decided to put in a new Fuel Rail Pressure Sensor and Fuel Pump Driver Module, but now the Fuel Rail Pressure Sensor reading is always at around 70 PSI when idling or off throttle, with dips in the 50s when doing wide open throttle (complete CSV data attached with graph for fuel rail pressure). Additionally, The Long Term Fuel Trims are very negative (-10% at bank 1 and -15% at bank 2), so I suspect that fuel rail pressure might genuinely be high because of the rich codes, strong fuel smell, and negative fuel trims. I am thinking it could be a bad Fuel Pump, but it could also be bad wiring around the Fuel Pump Driver Module and the Fuel Pump. Also, this may be unrelated, but my scanner reports 16V for the OBD Module Voltage, but my multimeter at the battery confirms a steady 14V. The car is also on an 87 tune, but it hasn't given any problems for a while before this.

Any guidance for further testing or for a fix would be greatly appreciated and thanks for your time in advance!

View attachment 112959

Hey,

The increase in fuel pressure when idling or engine running could be due to an exhaust leak. Given the system rich codes, a possible cause:

the fuel control system is adding fuel to compensate for a perceived (not actual) lean condition. This condition is caused by oxygen (air) entering the exhaust system from an external source. The O2 sensor reacts to this exhaust leak by increasing fuel delivery. This condition causes the exhaust gas mixture from the cylinder to be rich.

Also, look into other DTC diagnostic techniques here:

Adaptive Fuel Diagnostic Trouble Code (DTC) Diagnostic Techniques — 2008 Ford Mustang V8-4.6L Service Manual | Operation CHARM

Detailed repair manual for the 2008 Ford Mustang V8-4.6L.

charm.li

Particularly, the last example under subtopic Fuel System, for your concerns of P0193/FPDM higher duty cycle.

 

[FarrukhAnwar]

Thanks for the resource! I gave it a look over, but I couldn't find anything that fits my specific situation. I'll try to break each point down (I'll ignore all the lean sections as the engine is running rich) and please let me know if I make a mistake anywhere.

Using the LONGFT1 and LONGFT2 (Dual Bank Engines) PIDs
- MAF sensor seems to be working fine and reports around 5 grams/second at idle.
- Both LTFTs are negative and somewhat close to each other indicating a truly rich condition, but not necessarily a specific cause.
- Vacuum leaks are unlikely as the car is running rich rather than lean.
- Fuel filter seems fine as actual fuel pressure meets desired fuel pressure and there are not major positive LTFT corrections at high load.

Resetting Long Term Fuel Trims
- Already tried resetting Keep Alive Memory to no avail.

Air Measurement System
- As stated above, MAF sensor seems to be working fine and reports around 5 grams/second at idle.

Exhaust System Leaks
- I think an exhaust leak is unlikely, as it would cause an increase in fuel pressure immediately once the car starts, instead of increasing pressure only once the engine warms up after a few minutes, since exhaust leaks usually get better with higher engine/exhaust temperatures.

Fuel System
- Car uses a returnless fuel system, so there is no external fuel pump regulator. If the fuel pump has an internal regulator, it is also unlikely to be bad as the same issue was happening with two different fuel pump brands.
- I checked while the engine is running and there is no FRPS diaphragm leak.
- A fuel injector leak is unlikely as it would cause an increase in fuel pressure immediately once the car starts, instead of increasing pressure only once the engine warms up after a few minutes.
- EVAP purge valve isn't an issue as I disconnected the hose going to the intake manifold and it made no difference while the car was running.
- I also believe my FRPS is working correctly and not underreporting pressure, as my physical fuel pressure gauge was consistently 10 PSI under the reported fuel rail pressure at all PSI values (difference most likely due to the intake manifold vacuum).

One interesting thing I noticed while recording data is that the FUELSYS and FUELSYS1 PIDs report Closed Loop while idling, whereas the FUELSYS2 PID reports error. Is this normal or could this have to do with the PCM asking for more fuel rail pressure?

Graph for idling for 40 minutes with some revs in neutral at the end (full CSV data attached).

 

[FarrukhAnwar]

Update: it looks like the increasing desired fuel rail pressure is a programmed response to increasing fuel rail temperature. The desired fuel rail pressure starts increasing when the fuel rail temperature hits 84 degrees Fahrenheit, and the relationship between a specific fuel rail temperature and a corresponding desired fuel rail pressure is consistent across runs. This is both with the stock and performance tunes.

 

[luigui]

Have any oder update man my 2010 is doing same thing high fuel prssure stay in 430 kpa but when cool start fuel pressure is normal at 270kpa

 

[FarrukhAnwar]

No other update, I don't know what to do either. The PCM asks for higher fuel rail pressure when the fuel rail temperature increases, which is because the engine temperature increases (even if it stays within the normal range), which just seems inevitable. It seems the only way to stop getting the code is maybe by tuning the car to ignore high fuel rail pressure.