Can't get rid of P0301

Maintenance/Repairs
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1

I am at about my wits end with this P0301 (Misfire On Cylinder #1) code on my 2003 Ford F150 4.6L.
I’ve replaced the coil pack on that cylinder, all the spark plugs, and
replaced the fuel injector on that cylinder. We keep clearing the code
and it keeps on coming back.

The weird thing is that it only misfires after the truck has set for a
few hours and then it only misfires when I first put it in gear. Once I
am out of the driveway and on the road it’s fine for most of the day
unless I let it sit for several hours and then it might misfire again.

We noticed that the connector to the fuel injector is wobbly and doesn’t
snap tight to the fuel injector (before and after it was replaced) due
to the clips on the side not working well. We zip tied it together this
afternoon to make it fit tightly to the fuel injector to see if that
works.

Any ideas as to what could be causing this? Other than that misfire the engine sounds great and the trucks runs very well.

2

Dump a can of SeaFoam in the gas tank the next time you fill up.

http://seafoamsales.com/sea-foam-motor-treatment/

There may be carbon deposits on the back-side of the intake valve for cylinder #1 causing a misfire on a cold start.

Tester

3

Before replacing the fuel injector I put some sea foam in twice when I fill up. I did not use a whole can however just a little bit each time.

4

Dump the whole can in!

Tester

5

The only thing that comes to mind that is cylinder-specific and cause an intermittent problem is the crank position sensor. Other than using an event recorder, or getting lucky, I don’t know how you’d definitively nail this one down. A CPS is under $20. Far, far less expensive than an event recorder.

NOTE: this is just a suggestion, not a diagnosis. :stuck_out_tongue_winking_eye: