2002 Ford Expedition - service engine soon light came on. I went to Autozone for them to read the codes...it came back O2 sensors, ignition misfire, and fuel injector problem. Ocassionally, I will have white smoke coming from the exhaust, but after the car warms up it stops. Not sure what the problem really is. Any help would be greatly appreciated.

80 % of all O2 Sensor Codes are from Vacuum Leaks
or EVAP System Vacuum problems

Engine misfires also set them, to protect the exhaust converter

Have a repair shop get down to the real issue

O2 sensors both but couldnt tell you if its upstream or down stream.

misfire likely, but please have the car scanned for trouble codes and report them back to us. Many parts stores, such as autozone and advance will perform a free scan for you.

Sounds strange for all of that to be happening. The valve covers might need new gaskets. If you have a misfire, it could cause the O2 sensor to have a bad reading. Usually it's only 1 or 2 coils. (I would also replace the associated plug if they change a coil.) You could run it from there and if it doesn't clear up, then replace the O2 sensor at that point. Given the age of the car, getting the O2 sensor out may be a pain because it may be rusted/frozen in. Ford didn't believe in doing a good job putting anti-seize on the O2 sensor heads. Mine stripped when trying to replace an O2 sensor, so rather than have to replace a whole section of exhaust, I went to Midas and had them cut it out and weld in a new piece with a bung for the new O2 sensor.

running rough means it is misfiring.does it run smoothly without load or at idle?If it does then better check you fuel pressure as the engine needs more fuel under load.

Take the vehicle to any local auto parts store that will read the codes. WRITE THEM DOWN, and report back here for further help.

get a new mechanic, need to check for vac. leaks, poss needs tune up. alot O2 codes i have gotten have been created by vacuum leak or warn out plugs, rarely have i had to replace a O2 sensor.

Code P0301
Ignition Coil Pack
Ignition Cable
Spark plug
Clog or dirty fuel injector
Evap canister purge valve
Engine Compression
fuel pressure

you have 3 type of engine for your truck
2.3L 4 cylinder
3.0L 6 Cylinder
4.0L 6 Cylinder

need to know that type Engine

The reason why the service light come on because it is a hard code
not a soft code.

Let me know

I have a ford 2003 windstar that was running very rough when cold and almost stalling. engine light came on. went to autozone and they read the codes for free and told me it was running lean on Bank 2 also. i came home searched for the O2 front sensors online using the info autozone gave me. there are 2 front sensors on my car that need to be replaced at the same time. look for ones that have a direct plug in and don't need wire splicing. the ones without the wiring harness are cheaper but more of a pain, i think.
they were fairly easy to replace. getting access with the wrench was the worst. reset the light by disconnecting the battery for a few minutes. seems fine now and the light hasn't come back on.

http://www.2carpros.com/first_things/check_engine_light.htm