72gavek

Ok, 5.4L 3v owners and or mechanics I am at a complete loss!!

I have a 04 FX4 and recently did the plugs(zero broke!!) and all 8 COP (summit racing brand) truck has 138k and and 2 days ago it started sputtering in overdrive on the highway over the next 25miles of driving it got a little worse so I took it AZ to get the codes read and got P0171, P0303, P0316 the only one that made sense considering the work I just done was the crank position sensor, so I bought that and put it in and started her up and instantly you could hear the sputter. It idles really low and does ok when I put my foot in it but with out my foot in the gas you can hear and feel it struggling. I am a do it myselfer but am a complete loss!!! Anyone have any ideas or have had similar problems????

RLXXI

Clear the codes, a lean code followed by cylinder 3 misfire usually indicates a bad plug or cop, since you replaced them all I would take#3 coil out and swap it with another cylinder and see if the misfire moves with it, if it does you have a bad coil, if it stays on cylinder 3 pull the plug out and check the ceramic for cracks. Run codes again after you drive a few miles.

If that proves to be OK you may have a bad injector or weak compression on that cylinder.

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72gavek

Thanks, well today I was able to drive some more till the light came back on, checked the code again and now I only have 1.. It's the P0171. I cleaned the air flow sensor with the correct cleaner but don't know if it's that sensor or one of four O2 sensors!?!? I might just have to bite the bullet and have it professionally tested. Do you know if that would give me a exact answer to what's bad?