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Ron
Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 33435
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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I have a 2005 f350 with a 6.8l. I have a p0191 code, also

Customer Question

Hi I have a 2005 f350 with a 6.8l. I have a p0191 code, also had a p1237 code. I replaced the fuel pump driver module and fuel filter, and checked wiring. Reset codes and ran the truck. It starts and ifles fine but has a misses under power anywhere from 2000 to 3000 rpm. The p0291 code came back, but my scanner can only read codes. Freeze frame of both times the code happened shows 69 and 74 psi fuel rail pressure but engine rpm at around 700, (idling). Also when the key is turned to the on position, the pump runs continuous. There is no acces port to attach a gauge on these years, so any suggestions?
Submitted: 4 months ago.
Category: Ford
Expert:  Ron replied 4 months ago.

Hello Rick and thank you for your question,

The most common cause for these two codes to set in most cases due to either a failing FPDM or the fuel pump and since you have replaced the module then I would suspect the problem with the fuel pump. If its running continuously its likely because the pressure is not right and the fuel is foaming from a failing pump. Before you replace anything else run through the steps in the link below to recheck the FPDM and the circuit to it and the pump.

https://dl.dropboxusercontent.com/u/104923897/Fuel%20pump%20trest%20Jul%2020.pdf

Customer: replied 4 months ago.
Ok the question I have is why, at the time of the code, is the fuel rail pressure reading so high (around 70 psi) even though the engine is at idle. I would like to verify the rail pressure with s gauge but there's no fittings.
Expert:  Ron replied 4 months ago.

Usually due yo a false reading from a foaming fuel pump or the FPDM is defective. I would run the steps and see what you find. I suspect the pump is failing.

Customer: replied 4 months ago.
Yeah thats what I'm dreading. If scanner reads 70 psi at the time of the code, that means the fuel rail pressure sensor read that, and isn't the sensor what ultimately drives the pump module which controls the pump? Can I rule out the ecm interpreting the sensor incorrectly or sending the wrong signal to the pump.
Expert:  Ron replied 4 months ago.

I think you can if the sensor is sending the wrong reading. Spend a bit of time and run the steps I sent you and see if it will help you narrow this down.