I have a 2000 f150 with the 5.4. It has the P0171 and P0174 lean codes in it. Earlier it had a couple o2 codes as well. I had it to a local shop and they replaced the o2 sensors and put a MAF sensor in it. After 20 miles or so the lean codes came back but not the o2 codes. it doesn't run rough anymore but still has the lean codes. The freeze frame data for when the codes were set is RPM-1435 Load- 97.3% Coolant 194 St Ftrm1 8.6 Lt Ftrm1 25 St Ttrm 2 1.6 Lt Ftrm 2 25.
At idle the fuel trims are St 1 -1.6 to 0.8, Lt1 4.7-6.3, St2 -1to .8, and Lt2 4.7. what would be the next things to check and eliminate? thanks

 

Check for vacuum leaks. Most likely place is the PCV elbow behind the intake.

 

I'm not an expert but, it looks like the fuel trim is okay at idle and I think this indicates that there is no vacuum leak. From the videos I watch I think if there is a vacuum leak, the fuel mix will be lean at idle and will be okay when the engine is revved. Maybe a real mechanic will chime in.

 

Based on the FF data, look for a weak fuel pump or a restriction in the fuel delivery sub-system.

 

Good point. Replace the fuel filter, test the fuel pressure with a gauge.

 

If you test it with a gauge, be sure to test it when the engine is demanding more fuel, ie, at speed and under load, if possible. A pressure check at idle is likely to not show up much.

 

I changed the fuel filter and hooked up my pressure guage. It has 24 psi at idle and gets as low as 18 when at highway speeds and I step on it. Looks like I need a fuel pump.

 

Pull the vacuum line off the FPR and recheck.

 

The pressure went up about 4 psi at idle when I removed the vacuum line on the regulator

 

If that's all it went up, the FPR is good, you probably do have a weak fuel pump or a blockage somewhere in the system.

 

Replaced the fuel pump this morning. Fuel pressure in the mid 30s and fuel trims are back to normal. Thanks for the advice guys

 

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I think you posted in the wrong thread.