449SCREW02

I keep getting a service engine light. P0171,p0174 lean codes. I have replaced or serviced or inspected the following: intake and head gaskets, vacuum lines, fuel system, maf sensor, air and fuel filters, o2 and fuel pressure sensors. Oh, and I have been running no ethanol 91 octane for weeks. The code clears by diagnostic clear or by disconnecting neg battery cable. Runs beautifully, for 150-800 miles before the light comes back on. Light will not clear itself on an extended drive. I feel like my next step is to take it to ford and have the computer updated/flashed. Any thoughts? Anyone else have this going on?

ddbrown

Only issue I had with lean codes was after cleaning and re-oiling my K&N filter. (I over oiled it) which caused the lean codes....

otto457

Are you tuned to run 91 octane? It probably doesn't have to do with the lean condition but it's not helping anything.

paker

Since both banks are lean, the first thing I would check is a leak between MAF and intake manifold. Also, read fuel trim numbers. If they are high, leak is likely.

449SCREW02

My mechanics looked at all of the levels and found no issues. I haven't checked the gas cap gasket though. If that gasket was all dried up or cracked, could that fire a code?

01SUPERCREW5.4L

I have a 2001 ford f150 5.4l 2wd supercrew gave it a wash a couple days ago and noticed shortly after a bad misfire ., checked out the cop's and none were bad ., it started getting worse slowly . Changed fuel filter egr speed control and selenoid , cleaned maf sensor throttle body and replaced pcv valve and replaced k&n filter with fram & still nothing if anything it got worse ! Trying to eliminate everything befor checking out 02 sensors and could the iac sensor have anything to do with it ? Tried finding a vaccum leak but was unable to pinpoint anything . Idle is small misfire and in drive it is horrible ., even at full throttle it struggles to accelerate . Never had a problem befor other than a bad coil wich i replaced ., getting a p0171 but cant pinpoint the problem .. Help !!

akdoggie

You are lean, so I'd go to the EGR after the MAF sensor. I'm thinking that the EGR, possibly the sensor, is probably throwing these codes.

01SUPERCREW5.4L

Well took my truck to the local shop and he told me coils 8,7,and5 were bad along with new plugs and boots for the other 5 cylinders .. Paid 65$ for diagnostic took it home replaced plugs and coils8,7,and 5 . Runs way better except a lil mis still there , went ahead and bought another coil for cylinder 6 because it didnt look too good ... Runs like a champ now !!! All together after buying a new fuel filter egr selenoid & speed control sensor ., 4 boots & 4 coils . About 400$ in after taking it to shop i would say look at your coils or boots first befor dropping any $ on parts i learned the hard way but atleast im ahead of the game now as far as egr parts go

449SCREW02

FINALLY!!!!!!!!!!!!!!! WE FOUND THE SOURCE OF THE CODES!!!!!!!!!!!!
it was my fuel pump all along. My mechanic took my truck over night on a very cold idaho night. he reset the code and hooked up his diagnostic equipment to my truck, he just started it cold and drove around until the light came on. the fuel pump was dipping down in fuel pressure, only for a split second, and only when it was very cold. so the truck still ran great, the only thing out of the ordinary was a slight decrease in fuel economy. i am taking it in to have the pump changed tomorrow, just to have that final peace of mind.

ddbrown

I would keep that mechanic...most don't take that amount of time to diagnose an issue properly.