I have a 2008 4.7L, the check engine light comes on and flashes for about 30 seconds and goes back to just staying on. It starts to flash when I get to about 30-35 mph and there is a knocking pinging noise then the light will flash, if I let off the gas the noise goes away. I am getting codes p300 and p303. I have changed the plugs and swapped the plug wire and coil pack to a different cylinder and still get the same codes telling me cylinder 3. Any help would be much appreciated.

 

Well the blinking CEL is telling you that you are having MAJOR misfires and usually means you should back off the throttle until it stops...

What plugs did you change to? Copper? Platinum? Iridium?

You might want to have a compression test done to make sure everything is okay in there.. especially on cylinder #3 (P0303)...

There can be many many causes for this DTC so a compression test will rule out the very expensive and time intensive issues. I would personally start there.

If the compression test comes back bad, have the shop do a leak down test to identify where the problem is, which will give you conclusive results as to what is going on.

 

You really don't want to drive it. Flashing check engine light is catalyst damaging miss fire, Agree w/Izero on doing some checks.