Truck is a 2003 F150, 4.2L engine, 2wd short bed/short cab, auto transmission. Just bought it earlier this year. It started out with a P0171/P0174 code - I was worried it was an intake gasket leak, but found that the PCV was pretty fouled and replacing that got rid of the error. Shortly after that, I drove from Detroit to Chicago and back with no engine issues. It was driven a few times after that, but for the last two months it's really only been driven for a short while, once a week. Drove it to work today and got codes, P0171/P0174 came back, plus now P0302 and P0316 (misfire cylender 2, misfire on startup).

I have a spare coil pack, injectors, and MAF from a 2002 V6 that I scrapped earlier this year, so I can actually throw some parts at it for just time on my part. I did spray clean the MAF when the issue cropped up earlier this year, and didn't seem to have any effect then.

Should I pull the spark plug and check it for anything? I know the two lean codes tend to indicate intake plenum bolts, but would that issue cause the misfire on startup?

The truck drives fine - it didn't seem to have any stumbling or loss of power, although my drive in is only about 3 miles. It does sound a bit like a diesel, but it's done that as long as I've owned it. The truck is my winter daily driver, so I want to get this ironed out while it's still nice enough to work on it myself.

 

I would say that your misfire code is causing your P0171 73 codes so focus on the misfire
Make sure the plug is good and seated properly. Also the connections clean and, yes, use your spare coil pack. Could also be a dirty fuel injector or other fuel system problem. I would run a bottle of fuel injector cleaner through the next tank of gas and then change the fuel filter. cheap and good maintenance even if it is not the problem.

 

Plug wires seemed good and I ran some Techron in the tank. No major change. Some other searching dug up that plugged EGR openings in the header were sometimes a problem. I figured taking that all apart was a good way to check that as well as the state of the air plenum gaskets, for a fairly low price. Three of the 6 EGR openings were clogged completely - could not get a q-tip in without first using a small drill bit to break through. I got them as clean as I could, vacuumed them out a little, and started sealing the intake up tonight. Ran out of light, so I hope to see if this works (and if I got the truck back together correctly) tomorrow afternoon.

 

Yep, I'm going to say confirmed, those clogged EGR openings must have been causing the issue. I drove a good loop this weekend and the long trim fuel values stayed low and no codes came back up.

Unfortunately, having the battery off while I did the work made the PATS unhappy - now the doors will not unlock off the fob. I would just reprogram them, but I can't find my second key... another day, another project.