F150Torqued

I'm not so sure either. Reading up on the P0451 code in the Motorcraft OBDII Theory of Operation Manual enlightened me about yet another intertwined software system in the PCM. It seems it constantly compares the sum total fuel volume from injector flow pulses to the fuel tank level and a theoretical corresponding change in tank pressure as the fuel liquid volume decreases. Seems the Fuel Tank Pressure sensor will produce OTHER codes for 'opens' / 'shorts' or 'noisy' circuit. But if readings from it are not "RATIONAL" (with ref. to fuel consumption) - you get a P0451, according to page 41 of that manual. (if you don't have - You can download this manual for your model from here: https://www.motorcraftservice.com/freeresources/obd ) Page 41 also has voltage reference readings.

The attached "Diagnostics Reference Chart" from my factory service manual shows FTP sensor input is on pin 'B65' of the Body connector to the PCM, and page 41 of the referenced manual gives voltages you could expect to see.

Attached is also a component location chart from the electrical component manual.


It's unclear what you have replaced, or 'just checked' and how, to attack a P0172 code. If you 'replaced' injectors and O2 sensors, it's reasonable to assume the PCM could maintain proper fuel flow unless injectors were replaced with very high flow models, OR unless pressure was way high. And I don't see any way the IM could contribute to a P0172, (lean yes, but rich NO).


I think you need more diagnostics _DATA_ to avoid throwing parts at it. If you have a scanner or can get some live data similar to what @mavrik2747 was collecting in posts of this thread, it would sure help. You should check actual fuel rail Fuel Pressure (relative to vacuum), Fuel Pump Duty Cycle, and fuel tank pressure.


Hope this helps.

nnuzzo141

Thanks for the advice, I'll definitely try to data log the truck this coming week. Too clarify what's been done to the truck though: the first stored code was a p0172 code. Drove the truck again and the p0175 code also showed up. Cleaned the MAF and reset the codes by clearing the code with my reader and disconnecting the battery. Codes came back again. Checked the truck for vacuum leaks or broken connectors and cleared the codes, this time an o2 sensor code came up, both upstream. I changed the driver's side but couldn't get the passenger side out. Regardless the p0175 code remained even after I changed the o2 on that side. At this point I snagged the MAF from my friends truck, 08 5.4 and put it in my 06 5.4, did nothing. Next thing I figured to check was injectors, pulling the fuel rail off a bolt broke and I was unable to drill it out. After 10 hours and over 15 bits I gave up and got the dorman replacement intake manifold. Replaced all 8 injectors while I was at it. Put the truck back together and forgot to plug in the fuel pressure regulator on the rail (hose and connector). Truck ran fine apart from the obvious codes associated with that part and the p0451 code pending. I monitored the long term fuel trims on both banks and they were fine. Well below the threshold.
​​​​

F150Torqued

BUMMER. And, that bank1 upstream O2 IS a tough one. I've done mine twice in its 220k mi.

You still gettin' the P0172 & 0175? Not supposed to get those unless fuel trims are out of whack (exceeds -25% LTFT and -10% STFT for several seconds).


RE: FTP. What scanner are you using. If its Torque Pro, I've been hacking the hell out of mine for years and have identified several PIDs that might be helpful.

nnuzzo141

Ive been using a harbor freight scanner that can monitor pids, have the stuff to use the torque app but never managed to set it up