Hey everyone I just bought my first Ford focus ever it's a 2012 se hatchback it was listed as having a misfire so I checked it out and at first it said cylinder 1 and 2 mis fire and Catalytic. converter threshold too low. So I tried swapping coil packs around and nothing changed on the codes same 3. Then I got it home and put new plugs in it then it stared saying misfire on 1,2 and 4 and cat threshold so I bought new injectors and replaced them all. Now they car runs great its definitely not misfiring anymore or not as bad bc there is a noticeable difference in the motor once I start driving ill get a flashing cel and I checked it same 4 codes cat and 1,2,4 misfire. I even shut the car off turn on ignition clear the codes shut the car off and turn ignition back on but not the start the car and those 4 codes come back immediately. How's is that happening when the car never started so how does it know its missing I'm so lost and confused.

 

There are some systems that run a system check before the engine is started `and if something is not right the check will flag it.

Could be wrong , but I suspect there may be a poor connection problem and the job is to find it.



You might check the plug that plugs on to the alternator for arcing at the connections. This drives the computer nuts with electronic noise and could stand checking the plug for loose connections where it contacts the pins in the alternator.