Im sure that this has been discussed before however I am new to the forum.

I have a 2015 Gt 56k miles with just a CAI, sct x4 tune, resonator delete and axle back mufflers. I have a check engine light that comes on when I’m doing highway driving for like 30-45 mins.
It will throw a P0308 code. The check engine light will appear solid and not flashing then will go away within a day but always re appears when I’m driving on the highway.

The car never ever feels like it’s misfiring or I don’t feel a loss of power. I have swapped the coil and plug from cylinder 8 to cylinder 7 and the still get a misfire code sometimes for cylinder 8. I haven’t tried swapping the injectior as of yet. Looking for some insight thanks all!

 

Is the misfire bad enough to "feel" it? Consider checking the integrity of the ignition wire feeding #8. 12-volt wires go bad just as high voltage wires can. Seems like it's rather intermittent, like an intermittent "open" in a harness connector. Ford Diagnosis info includes "wiggle-testing" of connectors. imp

 

Nope I never feel a difference or any type of loss of power when the check engine light comes on. And it only comes on when I’m on the highway for like 30 mins or more but again the car still drives regular, then the light goes off without me clearing it when I’m just driving around town within a day. I’ll try the wiggle testing.