I have a 1993 F150 with an Inline 6. When I first start it up it runs fine. It seems that when it warms up after about a minute down the road my check engine light comes on and it runs like crap. As a result I am getting about 12 mpg. The motor is a new long block with about 25,000 miles on it. I have been battling codes for some time. I had Auto Zone pull the codes and I got various codes at different times.

I have replaced the following based on codes:

EGR valve
EGR position sensor
O2 sensor
Plug wires
EGR vaccuum reg

I am missing something? It seems like everything is fine until it warms up and something kicks in. HELP!!!

 

Is your engine warming up fully? Do you think the thermostat could be possibly be bad. If the thermostat is not working properly or the water temp. sensor is bad it would run just as if the motor is still cold.

What codes were you getting? After you replaced those parts did you still get the codes?