My truck (03 F150, 4.6) started misfiring a couple of weeks ago. I pulled the trouble code and it had a misfire on cylinder 3. I narrowed it down to a dirty injector. Swapped it out with a spare one that I had and it seemed to do much better. She started feeling a like it was running a little rough again, so I put a can of Seafoam in the tank. Truck ran great...until the next fill up that is. Rough idle came back and when I cranked her up a couple of days ago I had traveled less than half a mile when the check engine light started flashing on me again. I drove straight back home and hooked up the code scanner.

I got this laundry list of codes: 1. P0401, 2. P0171, 3. P0175, 4. P0302, 5. P0172, and last but certainly not least 6. P0301. So now I have misfires on two cylinders!

Here is a little history on the truck. It sat up for probably close to a year before I got it. The motor was shot, so I got a low mileage one from a local yard. The mechanic who put it in for me said that it was the best used motor that he had ever seen. It had low (verifiable) mileage on it, and had apparently been serviced with all Motorcraft parts. When I got the truck the gas was so old that it had that old gas stink to it. I drained, by unhooking the fuel filter (which I changed) and bypassing the relay, the tank as best as I could without dropping it and everything seemed to be fine.

Aside from the codes that I have, I also have an odor that smells like oil burning off exhaust coming from the truck, but I can't seem to find a leak.

Sorry for the long post. Any suggestions would be greatly appreciated.

 

Based on those codes, lean codes, a rich code, misfires and insufficient EGR flow I recommend you do these things:

1: For the p0401 with the truck running apply vacuum to the EGR valve with a red or black vacuum line that will have vacuum at all times, not just when EGR is supposed to be applied. When you apply the vacuum the EGR valve should open and the motor should bog down and want to stall. If it doesn't take your intake tube off and open the throttle body and with a flashlight look at the two ports on the right side (when looking in) and see if they look all clogged up with carbon, if so that's your p0401. If not pull the EGR valve off and stick a screwdriver in through the hole behind it and make sure it's not plugged where you can't see, and if you're satisfied that the ports are all clear, you have a bad EGR valve.

2: Did you use new spark plugs and wires? If not and they're old do a tune up. I think you should at least clean your MAF, because the lean codes on bank 1 would be caused by the misfires, but lean bank 2 and the rich code doesn't make much sense so especially if you put an oiled filter on, clean that MAF sensor.

However, I also think that your bad gas situation could be the sole problem with the misfires and lean/rich codes, so you should find a good fuel stabilizer product and pour that in your tank and you might have to change your fuel filter again because if there was crap built up in the tank and you just washed it all down it could have plugged the filter up that fast.

Keep all that in mind while you decide what to do first.

 

For the EGR code there is a sensor call PDFE you will see to lines coming off the EGR tube to a sensor that's Probly your issue there exhaust leak will course lean codes with the EGR not working properly more than likely a broken stud at the head you can usually see it under side of the manifold at the rear mostly take a look feel around sometimes the manifold will rot out aswell as I just had to replace mine for the same issue

 

I fnally got a chance to tinker with the truck this morning. I didn't do much. What I did do though was systematically unplug the COP's. One by one. On every one that I unplugged the truck ran noticibly worse. Same thing when I did it with the injectors. I cleared the trouble codes, ran the truck for a few minutes and reread. Now I'm getting the P0171 and P0304. I really wouldn't think there is anything wrong with the injectors or the plugs/COP's since when I unhooked them one at a time it caused the misfire situation. Furthermore, just by clearing the codes and re-reading, the misfire switched from cylinders 1 & 2 to 4. I believe that the DPFE sensor is my P0171 problem, and will try to pick one up today. I just don't understand the misfire issue.

 

Mine did that on my 4.6. All the plugs looked fine, but it would still misfire. Check the gap on them, that ended up being my problem

 

I thought abouth that last night too. I have a tester to check the COP's also, and it hit me last night that I should probably use it! If it ever quits raining here I might be able to track down this problem.

 

I think I got it running right again. I started by pulling all the plugs on that side and adjusting the gap. When I got to cylinder four I noticed gas on the plug. I knew right then that that cylinder was definitely misfiring. I hooked up the tester and sure enough the COP wasn't doing anything. I had an extra one (left over from the motor swap) so I hooked it up and tested it. Cylinder four misfire corrected. Truck was still running a slight bit rough, so I cleared my OBD codes and took her down the road. Within a half a mile or so I got a flashing check engine light. Came home, hooked up the scanner and it said misfire on one and two. Now I went back to my spare parts inventory and grabbed four injectors. I took a few drops of fuel injector cleaner and put it in the hole of the spare injector. Then I used a nine volt battery to operate the injector to cycle the cleaner through. When I got a drop of cleaner out, I let the injector sit for a couple of minutes while I did the same procedure with the other three. Two of the injectors wouldn't give up anything, so I used the two "good" ones. The truck is running better than it has since I got it. The motor is smooth as silk, no vibration whatsoever. My 0171 code hasn't even come back ( I never got around to getting a new DPFE sensor).
Of course, just to let me know that I waited too long to fix her, the truck decided to black out the odometer on me. Should be an easy fix there though!