About a month ago, I purchased a 2017 GT CPO from Dallas. About a week and a half in I was already having issues, but the worst of them all was the misfires. Codes are P0316 and P0308 which is misfire at startup and misfire on cylinder 8. The first trip to the dealer, they swapped the plugs and coils for 6 and 8 and tightened the air intake or something like that because it was loose. Misfire continued. Went again to a different dealer, they swapped the manifold and gasket, the CEL is no longer there, but the codes are still up when you check with an OBDII reader. Could it still be fixed and the codes just be residue? Do I have to just wait for those codes to go away themselves assuming it’s been fixed, or is it still misfiring since the codes are still up? Appreciate any input. On a side note, my car is completely stock aside from an axle back, but even before that exhaust install, a squeak/creak developer in the rear. At first I thought it was as the rear suspension, but now I’m not so sure. What could it be? Another issue is the bump steer, it’s awful. I don’t feel like it was this bad when I got it, but I’m not too sure. Do mustangs just have bad bump-steer from the factory or could this be another issue? I drive around 7 different cars on a regular basis and none of them have bump steer like this mustang, not even close, except for the ford transit van which makes me think it’s a ford thing. Although the van is still not as bad as the mustang. The mustangs steering also seems to “stick” sometimes. For example, it’ll out of nowhere just stick a bit to the left and it almost feels like the car chose to do that itself. It takes some force to get it back straight. I read this is just due to fords awful implementation of electronic steering, but I’m not sure, seems very unsafe especially on the highway. The last issue is this weird sound I can’t describe, almost like a sizing or boiling sound coming from the rear. What could it be?

 

Forgot to mention, an alignment was done and didnt help. Also, Meant to write SIZZLING or boiling sound coming from the rear when driving on the highway at 60mph+.

 

i don't know much about the mis fire codes but if it is fixed it shouldn't pop up on the obd2. Also if your car is steering to the right and you already got an alignment, one of your wheels camber is off. if that doest help there could be a problem with your rear differential or subframe. Also the bumper steer should not feel how you described it if it is getting harder to turn one thing could be is that you need power steering fluid. i recommend your flush it and put new fluid. Another thing have correct tires is really important. I had an issue with my 16 gt where is would go more to the side. I corrected it by getting the camber and wheel alignment. On top of that i ran Michelin pilot 4 sport tires all around and when i went to go install them i got tire balancing. Little things like that help alot!

 

The car should have some type of warranty?

Is the car lowered? That could cause major steering issues.

OBDII Code P0316 is a misfire from the secondary ignition system. I.e. you may have a shorted wire that connects to the coil so, swapping coils/plugs wouldn't do anything. - Other potential causes, oil in the spark plug well

OBDII code P0308 is a mechanical misfire like an intake valve, exhaust valve, bad compression.

Sounds from the rear? Check the pads and rotors for uneven/bad wear patterns or even a stuck caliper.