Hi everyone, I'm new to the Forum, and hoping maybe you guys can help me out. I have a 03 F150 SuperCrew FX4 with the 5.4 Triton. My issue is I'm throwing 2 DTC's P0171, P0174. (Bank 1 running Lean and Bank 2 running Lean). On Idel the truck will run fine but every 30-45 seconds it will idel up to about 1200RPM then slowely idel back down to the 650 range, I've checked my front O2's and both seeme to be working fine. they will raise and lowe in voltage from .76 - .06 or so. and the Trim will match. Ive checked voltage on MAF and seems to be proper although Dealership said to remove my K&N Filter because I was getting too much air. I Checked for a vacuum leak around the plenum and can't find anything. everything seems to be in good condition. My STFuel trim hovers between (-4% - +7%) depending on throttle input. But LT Fuel Trim averages around (19% - 25%). Except on WOT then it drops to 5-7%. I've Erased the CAM (Pulled positive off battery and left lights on for 15 mins to drain resisters and so on) After doing so the DTC's will show up again after about 50Kms of driving With same Codes. And the Fuel trims will be the same. I find the truck is hard on fuel, and also doesn't have the power I think it should have. Any reason why the STFuel trim would be fine and the LT so high??
I took the truck on Friday to my local Dealership and had a Scope and Diagnostics run on the truck. Mechanic says there machine says the truck is running fine and all the sensors check out ok. He sees the codes, and sees the LT Trim super high but had no explanation... He suggested replacing my Air filter with a Motocraft filter and dumping the CAM to see what will happen. then charged me 100$ Bucks... I did that... Back to the same issue... I'm going to call the dealership in the morning to let them know nothing has changed and the DTC's are still there, And truck is running the same way. Anyone have any Ideas???
Thanks
James

 

Your fault codes are among the most commonly discussed subjects heare.

Plug them into the SEARCH tool for hundreds of posts.

You will find that they explain all your symptoms.

 

Vacuum leak at the PCV elbow where it connects to the rear of the intake manifold or a dirty MAF sensor.

 

I've pulled that rubber elbow and assembly from the PCV off and checked it all.. All the rubber fittings look fine.. inside and out.. Only thing I noticed was @ the plenum the rubber "Elbow" seems to pull off (easily, not as hard to remove as the other rubbers) from the plenum. Possibly not a super tight seal??Would that make sense?? The condition of the elbow almost looks new with no corrosion or anything. I'll try a Gear clamp on it tomorrow night after work, to snug it up. MAF Seems to be reading correctly I have a programmer which allows me to monitor the MAF. Even the Dealership says it reads correctly. I have another appointment @ the dealership for wednesday.. they are gonna run another scan on it and try to diagnose it.. Thanks for the help ..
James

 

I would check the intake gaskets and the intake itself for leaks. Use a mist of propane in areas and watch the fuel trims to help find the leak.

 

Just got back from the Dealership... They told me they think my fuel pump might be getting weak.. and that's whats causing the Lean conditions and the Fuel trims to be so high... Does that make any sense?? I changed the fuel filter last summer when I first got the codes read from the truck. That was the first thing I changed and didn't effect the condition at all. Is there more then one fuel filter on the truck?? I changed the canister type on the frame rail on the drivers side.. Any suggestions???
James

 

Cornwall rc,
I've an 03 f250 S/d with the same problem, also idles up when dropped in gear,puff of smoke on start (hot and cold) and using oil. Runs great otherwise. Whats the answer? Thanks