Hello, I have been to this site a ton over the past couple years trying to chase down a gremlin in my F-150. It is a 2000 f-150 with the 5.4 and 145k miles.

The issue is a misfire that presents itself under load and it has been getting worse over the past 2 years. The engine idles fine (albiet starting to change) and when the PCM is reset and when driving without a lead foot it doesn't misfire. Currently it hesitates a little bit from a stop and when under load will misfire like crazy and shake you to death (large issues going 45+ MPH can't even hold cruise at 60 without it shifting gears), and when monitoring the timing at idle I get readings from 12-27.

I have replaced the following:
COPs 2x
the spark plugs
fuel pump
fuel filter
vacuum valve on fuel rail
intake manifold (due to coolant smell and mine had the plastic crossovers)
a couple injectors
o-rings on all injectors
cleaned the throttle body
cleaned MAF
checked vacuum lines
checked wires
cleaned and sealed cops over spark plugs
moved the wire harness away from the A/C condenser
checked 02 sensor voltage
check fuel trims while driving

Currently it is spitting codes p0353 and sometimes p0303. I can switch cops, fuel injectors, and spark plugs with no change in the way the truck runs. I am finally stumped and do not have the means to test my PCM without taking it in to the stealership so I figured I would see if you guys could help.

 

https://www.obd-codes.com/p0353

https://www.obd-codes.com/p0303

Read those if you haven't already. The second one mentions burned exhaust valve and low compression. A compression test may be in order.

You probably have a wiring problem to the coil though.

 

Thank you will check these out