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.

 

Have you tried doing a compression test?

 

Why not start by looking up what the codes are telling you?
401 is low flow failure of a test in the EGR circuit.
301, 302 are first two cylinders missfireing.
171 is lean bank 1.
172/175 rich banks 1 and 2.
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Since the motor was changed, there would be question if..................
First check if the connectors are seated on cylinder 1 and 2 coils.
Check to see if the connector is seated on the DPFE.
Your codes are from three different areas.

You have to start running them down.
Good luck.

 

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.

 

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!