I just purchased (TO SAVE $$$ on GAS) a 2003, F150, 4.2 liter, 5-speed with 88,000 miles on it. When I bought it, the "Check Engine Light" was on. No problem, I'm you basic shade-tree machanic. I went to Auto Zone and had them check it with their computer. They said I had a bad "Mass Air Flow Sensor". I wanted to wait and drive the truck a little bit, before I spent any money on it. So, I've driven the truck back and forth the work for a week (50 miles round trip) and it runs great. Checked the gas mileage, and its getting about 18.5 miles per gallon (alot better than my F350). So far really impressed with the truck. No Problems other than the "Check Engine Light". Yesterday, I went down to the FORD dealership and bought new plugs, wires, ignition coil, fuel filter, PCV value, and a new "Mass Air Flow Sensor" ($608.11). Went this morning and bought oil and filter ($108.20) Had my weeknd planned. On Friday night I replaced the "Mass Air Flow Sensor" and cranked the truck after resetting the computer, no more "Check Engine Light". GREAT!!! Got up this morning to finish the rest. 1st, replaced all the plugs (gapped at .52-.57 per owners manual). The original plugs looked okay and they were gapped .70) 2nd, replaced the wires. 3rd, replaced the ignition coil. Cranked up after replacing the before mentioned, now the truck is running rough, real rough. Went back and check to see if I'd crossed some wires and found where I did. (# 5 and #6). Came in and verified on this WEB Page the order. Passenger Side front to back 1,2,3, Drivers Side 4,5,6 on the motor. The ignition coil is dummy proof, they've labeled it. After verifiying all of this, still runs rough. Went back and pulled all the plugs, put the originals back in (same order they came out). Still runs rough. Put the orginal wires back on, still runs rough. Put the orignal ignition coil back on, still runs rough. When I say it runs rough, its idling fine, but when I'm running down the road, and get on the gas, it starts cutting out, BAD. I've even went back and put the orginal "Mass Air Flow Sensor" back in. Its still running rough. I've work on this thing all day now, and I don't have a clue what I did wrong. Right now, I've put all the orginal parts back on it, and it's still broke. Before and carry it to a repair shop on Monday, I thought, I'd post this to see if anyone has any ideals or suggestions. THANKS !

 

Sounds pretty frustrating!

I'd double check to make sure all vacuum lines are in place, secured and not cracked.
More than once guys have reported finding one or more of those as being the casue of problems like you describe.
All the banging and bumping around involved with your under-the-hood work makes it more likely that you might have a vacuum line off or loose (does that sound like the voice of experience talking? )

 

Well, I ended up fixing whatever it was I broke. On Sunday afternoon, I carried it back to Autozone and had them put it back on the computer,,,,, no errors or codes. Now I'm really stumped. Drove back home and on the way, I decided to take all the old stuff back off, and put the new parts back on before carring it to the dealership or repair shop. Put all the new parts back on,, cranked it,,,, runs perfect. Only thing I can think of, is I might not have pushed some of the Spark-Plug wires on the ignition coil down good enough. Basically I don't know what I did to break it, and I don't know what I did to fix it. Just glad I don't have to carry it to someone else and pay them to fix my screw up.

 

Chris

 

That's good news!
Glad you got it going.