fox7355

i put a e 303 in my 5.0 and now it backfires whenever i engine brake down a steep hill. I brought it to a local shop and they told me it was just the cam.

vristang

If they said that without looking at the car, then it was because they are too busy to do a trouble shooting diagnosis.
If they looked at the car and came to that conclusion, then don't go back to that shop for diagnosis issues.

Most likely you have the cam timing or ignition timing a little off.

jason