I just bought this 99 f250 super duty with 197k.
I changed all fluids and installed new spark plugs. I then changed the exhaust. I deleted the cat and replaced my muffler with a glass pack. Right after that I got a P0171. The pickup runs rough and jerks when driving it.
I cleaned the MAF sensor. I did replace the fuel filter. I check the pvc hose under the throttle body. It looks good.
What other hoses do I need to look at for vacuum leaks? I have read that it may be my O2 sensor.
It ran pretty good until I changed the exhaust. I did add some marvel mystery oil at the same time.
I did clear the code but still runs rough.
Another problem
My 4x4 light, service engine light does not come on when I turn the key on. All my other light come on then go off. My check engine light never comes on either.
My ABS light is on but I know what the problem is their. The left front wire going to the sensor is broke.

thanks for any help

 

Something's making it run lean.

Start by checking the fuel pressure, and make sure it's 28-30 at idle, and 38-40 with the vacuum disconnected from the fuel pressure regulator.

Any chance you have an exhaust leak ahead of the O2 sensors?

 

I will look into the fuel pressure.
I will look at the exhaust but I did not here anything.
thanks again for the help

 

Check the vacuum hoses on both valve covers.

 

OK will do.
On the passenger side does the hose crack under the insulation? Can I cut it off and then zippy tie it back on?

 

OK I am sorry for the stupid question but where is the fuel pressure regulator?
thanks