There are many reasons a code P0171 would be set.
The thing is to systematically narrow down this particular reason.
If this engine has recently been installed and all the other items were replaced at the time. The suggestion by jdl123 is a good one if the recently installed engine has been setting up a while this could solve your problem. If not I would check all of the exhaust manifold bolts. A loose one could cause air to be pulled into the exhaust stream pay close attention to the exhaust to tail pipe connection. Vacuum lines are also a big headache sometime on engine exchanges. Visually inspect the O2 sensor it self as well. A pinched or otherwise damaged wire on the O2 sensor may set this code
Tuesday, February 10th, 2009 AT 10:15 PM