no code; fuel pressure sensor

08 ford f150 4.6. Truck was acting like it was out of gas with no throttle response. problem was intermitent, some days I drove it without a problem. then i would get stumbling and black smoke out of the exhaust.Towed it to a shop and he couldnt get a handle on it either. finally after some website research i noticed " fuel pressure regulator" was a common denominator. I called in and requested that the part be tested and installed. he did and it worked. The thing that bugs me is no code was ever thrown and the truck was running extremely rough. to be clear the repair was a sensor and not a regulator if their is a difference. Also I know black smoke is a rich indicator, what should my diagnostic procedure have been.? part was 120.00 total job = 389:(
JE

Not having inspected the truck while the problem was present, it's impossible to say one way or the other. :silly:

But if I had to guess, I'd say the part that actually got replaced was the Fuel Rail Pressure Sensor. As you noted, there is no pressure regulator in this system, just the rail pressure sensor and a Fuel Pump Driver Module to control fuel pump output.

If the rail pressure sensor was skewed (let's say, reading 30 PSI when the actual rail pressure was 60 PSI), then you'd get black smoke and rough running from the excessive amount of fuel being injected. That's the first thing that comes to my head, anyway. Or, perhaps the sensor was skewed in the opposite direction, and the Fuel Pump Driver Module reacted by sending pressure though the roof? Again, it's tough to say without knowing the exact nature of the failure.

Can't say I've ever seen that specific failure happen to one of these sensors before, but anything is possible. As far as what your diagnostic process should have been? If the rail pressure sensor was skewed, then I'd like to think it would have failed a quick rationality test. A physical gauge on the rail would probably tell you the same thing. But it's easy to say this stuff in hindsight.

thank you for taking the time to respond. interestingly enough his summary on the invoice lists; fuel pressure test. However given the fact that he struggled to ascertain the problem it is doubtful that he did. On this vehicle there is no schrader valve to hook up a fuel pressure tester. you can employ a live data tool to "see' the pump pressure. I think faulty fuel pressure would have instantly indicated a problem in them and a follow up from there. again, why no code? there is a po code for this sensor. why the ECM never triggered it is beyond me

I also think you dealt with a faulty fuel rail pressure sensor. Beside from fuel pressure gauge as Tyler already mentioned a look at fuel trims, O2 sensors and duty cycle of fuel pump driver module might have been pointers for diagnostic direction.

For a code to be thrown the computer has to see the parameters.

Is the pump before this part where the pump kept up? I don't know these systems but that would make sense that it didn't go enough out of range to set a code.

You don't need a schrader valve to test fuel pressure. Google fuel pressure test kits and you'll be surprised and the adapters as well.

I have some pico pressure sensors and they don't need a schrader valve to work.

Maybe search the fuel pressure test procedure for this year, make, model (YMM) and it'll show how they commonly test it. Someone has probably tested and even diagnosed that repair on YouTube just guessing. Maybe see what process they used?

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johnt wrote: I think faulty fuel pressure would have instantly indicated a problem in them and a follow up from there. again, why no code? there is a po code for this sensor. why the ECM never triggered it is beyond me

I suspect you were experiencing an in-range failure. The sensor signal may have been skewed, but not skewed enough to trip any of the traditional P0190/P0191/P0192/P0193 codes that these sensors usually produce when they fail. For example, here's the code set criteria for P0191 on your truck:

www.fordservicecontent.com/ford_content/...orcraft/OBDSM804.pdf





The kicker is the monitoring duration - eight seconds. :ohmy: I dunno if this problem happened for eight seconds or more at a time? But that's a huuuuuuge amount of time when you're talking about catching intermittently failing components.

thank you! this is a big help! I didn't know about the three parameters. Just the same Im surprised given the poor state of performance the truck exibited. My judgement of this is biased based on the lenght of time it would take to throw a code for a coil. I do not have a nice data scanner to view the fields, but at this point that would have been my only option to get an indication of what was going on. thanks so much for your help, very appreciated. John E.