I just got this truck about a month ago with 107,000 miles on it. Previous owner just put in new plugs and coils.

Truck runs and drives great but after about 50-60 miles of driving it the engine line turns on with code P0300. I cleared the code once and it game back on after my next commute with it. Doesn't seem to throw the code if i'm just staying around town. Curious if it could be the new plugs and coils or if I need to look at the injectors.

2003 F-150 4.6 V8

Thanks,

 

We've seen this issue with Amazon/eBay/parts house coils. Do you know what coils and what plugs he used? These motors are a little picky with plugs and coils, and tend to want OEM pieces. The preferred coils are Motorcraft or Denso, and for plugs it's Motorcraft.

 

Just pulled a plug and coil have Motorcraft coils and plugs. It looked great but I didn't check the gap, didn't have one onhand.

 

Do you feel anything? Any mods under the hood?

Don't replace any injectors. The failure rate of injectors for your motor is effectively zero, plus there's a high risk of buying lower quality parts than you've already got. Sugar in the tank is about all I could imagine happening to them.

 

Well, that is the good news. The bad news is, you've got more questions to answer to figure out the issue. (See Ray's post)

Does the motor make any noises on startup, while running, etc.?

 

Random misfire code may be the Crank Sensor plugup is dirty up behind the Crank Pulley and subject to vibration.
Worth a look at, clean and reseating.
Good luck.

 

I actually just got a P0315 error for the crankshaft sensor. Going to replace that and see if that fixes it.

 

Loose crank bolt. Telltale signs would be an oily crank pulley maybe belt. The crank pulley bolt holds the CKP sensor tone ring in place on the crankshaft and a loose tone ring can set a 315. The sensors themselves don't set DTC's.