ive got a 1996 f150 4.9l thats throwing me p0171 and p0174 codes now ive rebuilt the motor replaced the gaskets smoked the vacume lines and have no leaks anywhere i replaced the egr and the egr vacume sensor. i did a fuel pressure test and am right on the money. the light will not go away unless i run a 97 octaine mixture and when i do that i throw no codes and have no problems untill i run out of gas and then i get my bank 1 & bank 2 lean codes. one thing i did notice is that i have an air charger sensor on my lower intake but ive looked at the harness and there is no plug or cut/melted off lines its just there any help or advice will do. like i said i rebuilt the motor to fix this problem every gasket and sensor is new and good and every bolt is torqued down to spec. the pic is the sensor that has no conector

 

Ford moved the ACT sensor to the air filter box around 1994. If your truck has a ACT in the manifold then it came from an earlier model. Since you have no codes indicating a problem with the ACT then I would assume the wires are connected to the air box mounted ACT sensor.

You have started several threads about this issue, I pointed out in this one: https://www.ford-trucks.com/forums/1...s-for-day.html that a dirty or faulty MAF could be the cause of the lean codes. As suggested before low fuel pressure could also contribute to the problem. What were the fuel pressure values when you tested it?

 

I clean the MAF sensor and on the obd2 it was reading just fine I also did the fuel pressure and it's coming out at 52 psi rear tank and 51 psi front tank I replace well you seen the other threads ive replaced mostly everything else and the fuel pressure regulator is also fine so I don't know what else it could be besides possibly the injectors I also appreciate your ongoing help with this matter

 

Were those pressures ever measured with the engine running and under load? It would be rare to have two weak pumps but I do not recall if you changed the fuel filter.

 

What brand spark plugs are you running?

In addition, and I'm not trying to be an *** here, but it's MUCH easier to keep just one thread going per issue you're having. Lots of people (me included), won't take the time or effort to search out other threads you may have posted. Lots of times, that results in people who recommend things you've already done...

 

I run motorcraft plugs and wires

 

Well, there goes my theory. I've had similar codes with cars that had Bosch or other supposed "better" plugs...

 

Have you replaced the O2 sensors?

 

I replaced all 3 o2 sensors on my truck