I have a 2005 F-150 5.4L 2WD 90K miles. I started getting a misfire and hard jerk when going uphill. No codes for a few days but misfire got a little worse and more jerking at full throttle acceleration or level throttle up a hill got codes p0300 and p0171. I replaced the fuel filter cleaned MAF and changed plugs Motorcraft plugs (none of them broke during replacment). Miss got worse. Missing at idle and no power 3K rmp to get to 40. Only code pulled was p0171. Replaced upstream O2 sensors and COPs. Will barely idle now. Dies when put in gear. Full throttle barely moves forward a few feet just sputters. Checked vacuum lines can’t find anything. Only code I get is P0171. Fuel injectors next? Or shop?

 

Check your cat. converters??

 

I loosened right side flange (bank 1) upstream of that CAT. It was loose enough to be able to see the 2 pieces of the pipe move away from each other and it had no change on the miss/no power. Did get really loud when I started it up so I think it should have relived any back pressure.

 

@Less99


In this situation it would be useful to have some OBD2 readings from a scanner tool. But short of that, it appears you have done all the right things.


The only other suggestion I have is (assuming you haven't already done it - as you didn't mention it) is to reset the PCM and do complete re-learn procedure. It is a common mistake to replace a weak or faulty sensor (which has been producing bad input signals to the PCM for thousands of miles), and then expect the engine to run perfectly on the PCM's severely adjusted values it has developed trying to compensate for the bad sensor or input. Review the thread at:
Battery relearn process - Ford F150 Forum - Community of Ford Truck Fans


The PCM has stored fuel "Trim" values for different rpm ranges, load conditions. After replacing O2's or other sensors, the PCM doesn't know that. It is then relegated to using 'BUM' values for injector pulse width and throttle position or cam timing, or may be trying to OVERCOMPENSATE the other direction from those BUM values. Some PCM's even have a "driver satisfaction" routine that tries to logically adjust parameters to satisfy the type driving YOU do. ALL that is out of whack after a major tune up.


I would disconnect the battery for a long period of time (even overnight) to make double dog sure the intermediate storage in the PCM is completely cleared, then go through the re-learn process.


After doing this on my truck (following an intake manifold replace) it took maybe ten driving cycles for it to settle down and clear up.


Good luck