Hi, I got a 09 f150 5.4 v8 with 193k miles. In the morning when it’s cold I start it up it runs rough for a minute or so but levels out and doesn’t run rough again. I checked the check engine codes and it shows up for a pending cylinder 8 misfire code. I moved the injector, coil, and spark plug to another cylinder and I still have the same issue. Any thoughts? Spark plugs are brand new
Do the compression test on that cylinder.
I forgot to mention that it has flowmaster performance headers from the previous owner. It sounds like it leaks a little on the cold start. Could that be the problem too? I’m going to pick up a compression tester asap
If you have an exhaust leak its gonna be there warm or cold. You sure your not hearing vacuum sucking noise? Vacuum leaking could do this. Check all your hoses for cracks, wear holes
I had a similar problem years ago on my 78 Trans Am with the 403 Olds Big Block. In my case my issue was on cylinder 7, ran rough when cold, or if I put my foot in it. Once warm under normal driving it ran fine though. Luckily mine was not fuel injected and when accelerating hard it would pop back through the carb. Which was the clue I needed to find that the cam lobe on the exhaust valve for that cylinder was extremely worn. Previous owner hadn’t done oil changes regularly. Oil port was partially clogged and not oiling properly on that lifter.
