Random/Specfic cylinder misfire
 

A little background on the car,It’s a 2011 Mustang GT with 54k on the clock painted in gloss black equipped with the 5.0L and a manual tranny. The car is lowered and has a preloaded 93 octane performance tune from SCT. The car just came back from the dealership with some major repairs done. Due to the lowering kit not being installed correctly the underside of the car was basically shot. Everything from the motor back was replaced or rebuilt luckily it was covered under a warranty.

So now the problem,Before the car went to the dealership it was throwing a cylinder 1 misfire code. When it came back things had progressed a little. The car is now throwing a random misfire code (P0300), cylinder 1 misfire (P0301), and a cylinder 6 misfire (P0306). First things first changed the spark plugs and saw no change, changed coil packs and nothing there either. Its worth noting that all 8 were changed of each. Hooked up the computer and looked in FORScan at the cam sensors and it showed no faults. I would have like to have been able to see the crank sensor, but I could not find it. Also looked at the injectors and it showed not faults but decided to check them anyway. I swapped injectors 1 with 2 and 5 with 6 and noted no change. Listening to the motor and noted a hissing sound and narrowed it down to the PCV valve. Went and picked up a PCV valve from the local auto parts store and installed it, it did stop the hissing sound but did not help the misfire problem. Now the second problem with this, the tune is locked on to the car. The flash tuner keeps throwing up a voltage error when trying to reprogram PCM back to stock. Spent a significant time on the phone with SCT and they went through a whole checklist including a force reprogram with no luck. Its also worth noting that they checked the stock file from the programmer and noted nothing wrong or corrupt with the file. The next option is to take it to Ford and have them flash the PCM and reload all the Ford programming, the catch is it’s a $130. If that doesn’t work, I’m thinking about going back into FORScan and watching the engine under load in that powerband and see if I can see anything wrong in the live data stream. If nothing there thinking about having it sent to have an EVAP test done to check for vacuum leaks. If nothing there thinking about having it sent to Ford and have them do a misfire relearn. After that I have nothing, so the question is how confident are you all about the tune being the issue? Am I thinking in the right direction with this? Any other ideas that I’m overlooking? Any thoughts, comments, questions, or ideas will be most appreciated.

Thanks in advance,

Eric

Hows the charging system (alternator) and the battery on the car? Newer stangs and fords in general have very sensitive electronics and any type of noise from a failing alternator or sketchy battery will throw the PCM/ECM into a hissy fit.

You may also want to trace the wire harness from the PCM/ECM and see if it's chaffed anywhere or if there are any chafed wires under the vehicle.Any type of short or chaffing could cause shorts or open circuits that would cause a bad signal to be received by the ECM/PCM and thus cause it to act weird.