Well, if the check engine light goes on, something is wrong.

Get the error codes out of the computer, and find out what is wrong. Could be 20 different things, us guessing with essentially no information is just going to waste our time and cost you money.

Follow this simple picture, then look at the codes list below:

http://www.midimonkey.com/~frederic/f350/eec-codes.html

The connector is under your hood by your driver side hood hinge. Jumper the two connectors as shown, then put the key into the ignition, and turn to "RUN". Not start, not acc, RUN.

Then watch the check engine light blink, and count the blinks.

Viola, there's your first code.

Turn off truck, turn back to RUN, watch blinking, get second code.

Etc.