Code P0191, under load transmission is bucking and kicking

Tiny
C DAVID LONG
  • MEMBER
  • 2006 FORD EXPEDITION
  • 5.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 240,000 MILES
Bought a "project" SUV listed above XLT. So far I've replaced the fuel rail pressure sensor, the Mass air flow sensor, and the fuel pressure regulator mounted on the frame rail. I'm still getting a P0191 code, with the transmission-like bucking and kicking under a load (or climbing a hill).

Also, in the last two weeks, I've done a complete throttle body cleaning and replaced a missing 20A fuse from F1.34 in the fuse box that reportedly signals the MAF sensor. (It was completely missing)
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Thursday, March 21st, 2019 AT 9:35 AM

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Tiny
JACOBANDNICKOLAS
  • EXPERT
Welcome to 2CarPros.

The code you have is related to the fuel rail pressure. I see you have replaced a few things already, so you already know what the code indicates.

If you look at picture 1, it indicates the possible causes of this code, other than the sensor or an issue with the regulator. Take a look through it.

With that in mind, have you checked for vacuum leaks? Although you have replaced the regulator, have you confirmed that the fuel pressure is within the manufacturer's specs? If the pressure is too low it can cause this too.

Here are a couple links that you may find helpful. I suggest you check for vacuum leaks and confirm pressure first. The pinpoint diagnostics for this code are pages and pages long. Hopefully, we will find it this way.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Here are the manufacturer's specs for fuel pressure.
Specification

Fuel Pressure
Key on, engine off .................... 240-310 kPa (35-45 psi)
Engine running .................... 193-310 kPa (28-45 psi)

Check these things and let me know the results.

Joe
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Thursday, March 21st, 2019 AT 7:35 PM

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