I got a 1996 f150 302 manual transmission 6 inch lift 32 inch tires and i am getting 6 miles to the gallon. My check engine light is on and i got CODES P0171, P1131, and P1151. I changed the cap and rotor, cleaned the mass air flow and cleaned the o2 sensors with brake clean and thinner. any have any suggestions on what to do next i would appreciate it Thanks!!

 

P0171 -- Too lean bank 1
P1131 -- No HEGO switch bank 1, too lean
P1151 -- No HEGO switch bank 2, too lean

The computer thinks both sides of the engine are running too lean. It doesn't seem likely that both oxygen sensors would get dirty at the same time. The computer doesn't seem to be flagging a misfire. You don't report any driveability symptoms other than poor gas mileage.

Two possibilities: 1) The fuel pressure is too low and the engine really is running too lean. Check it with a guage
2) The heater circuit to the O2 sensors is not working. The sensors will not warm up and will constantly indicate "lean". If the truck seems to be running rich, despite the codes saying "too lean", this seems likely a good possibility.

 

i Used my scan tool and watched the sensors movement and ther both jumping like they should. The exhaust smells very rich.enough to burn your eyes just walking around it. I pulled the plugs today and they look good, they must of been just changed. i just bought the truck so i dont know whats up with it.

 

Strange. The output of the scan tool says that closed-loop operation is working as it should.

Yet the exhaust smell, gas mileage, and codes say that it is not. Use your scanner to clear the codes. See how quickly they come back. If it is practically immediate then something is way inconsistent here. If it takes some driving before the codes come back, then maybe there is an intermittant failure, like a bad connection in the O2 heater circuit.

 

p 0171 is still there it comes on after about 10 min idling or driving in town i checked fuel pressure and its around 32-34 pounds i think thats kinda lowbut the book and alldata calls for 30-45 psi. i just wanted to thank everybody for the advice and if you can think of anythin else i should try please tell me. Another thing my temprature gauge fluctuates alot while driving so i changed the coolant temp sensor not the sender and no change. i know the sender goes to the guage but i just had a instinct to try the sensor since it sends a signal to the pcm. thanks again
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