I have a check engine light on my 03 F150 5.4 I checked the OBD & it read bank 1 to lean. I changed the O2 sensor checked all hoses for leaks & nothing. But I do have a little exhaust manifold leak I'm wondering if that would cause it. Can somebody please help me what can you tell me how can I fix it? All answers will help thanks!!!

 

An exhaust manifold leak could definitely cause the CEL you describe. The ECU is checking that both pre-cat O2 sensors are in sync and reading the same. If one is off for whatever reason, be it a stuck injector or bad coil or manifold leak, it'll trip the code.

As for the leak, what's leaking? Is the manifold cracked? Or is it a gasket? Whatever it is, replace it and (hopefully) you should be good.

 

Mine did the same recently. I felt like a retard when it turned out to be one of the hoses coming out of the intake that had come out of place.

 

The intake manifold bolts are notorious culprits. There is a rubber seal around them. The rubber deteriorates from oil (that can get sucked in from the PCV) & age causing a vacuum leak.

 

Thanks guys I ordered BBK headers & their going in this week!! I hope this fixes the problem!!