OK. Calling all you truck gurus. I have a 97 F150 5.4 4x4 Lariat. I just had a Reman motor put in. Everything is new and the check engine light is on. My mechanic could not figure out why this is happening. He suggested I take it to another. So I did. they have not found anything either. No one knows why the Check Engine light is on. Oh, it reads a lean code. Prior to the new motor, I had the same problem with the check engine light. O2 sensors were replace and 100 miles late the light comes back on. The "other" mechaninc suggested it may be a bad ECM and also suggested he would like to try some type of thing to see if it is the ECM. They have found no vacuum leaks of any kind either. Can anyone offer any suggestions.?

 

I had a similar condition in my 4.0 ranger, and after replacing the O2 sensors a couple times, it ended up being a wire in the O2 harness that was worn down and hanging on by a thread. There can be several causes for a lean code however, but making sure the wiring is in good shape is one place to check.

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