5.4 Triton consistently logging p0303. I've done the following, and continue to have the misfire on cylinder 3 over the past 2 years with increasing frequency:
- Coil replaced
- New coil swapped with cylinder 1
- New plugs
- New plug swapped with cylinder 1
- Injector swapped with cylinder 1

Through all of this, cylinder 3 misfires, and no other cylinders. I clear the code and it pops back up within 30 min of driving. Initially it would take a week or so to reappear, but more frequent now. There doesn't appear to have been any coolant leaking near the cylinders, everything is pristinely clean (I bought at 88k, unaware of issues before).

Suggestions on what to check next? Is it likely a wire fault somewhere between the computer and cylinder?

Any help appreciated, thanks!

 

Welcome to the site

What was the comp results ?

 

I'm not sure what's meant by comp results, but as stated the only logged fault is p0303. After checking around I heard sticky valves may result in this behavior. I tried a big bottle of Marvel Mystery Oil, and after 200 miles the light did turn itself off, though reappeared yesterday. I'm optimistic this is in fact the culprit and will try some other cleaners as well.

 

Compression test results

 

Ah, gotcha! I don't have the ability to perform that test myself, and not really willing to take it anywhere given that it seems to run OK. Since I've had decent luck with the cleaning products, I'll continue down that route, but if the code reappears consistently, I'll consider getting a compression test.

 

I could be wrong on this, but I believe Hayapower is suggesting a compression test because,,,,,,,,,there may be a problem with one of the valve springs for that cyl and a comp test just might bring that out.

 

Yeah hanky,, just as part of the elimination process.
Valve components would more than likely be a condition for continuous misfire, potential for rough idle, and possible accompanying noise. Unless a valve ‘float’ due to a spring or hang, that caused higher end misfire. But being the position swaps for the ignition parts etc, and some new resulted in no change, if not comp related it could be control related be it valve train, hardware or harness, driver issues and such.
If the misfire can be duplicated standing still/idle, to Lower RPM speeds (?), a vacuum gauge test with erratic readings may point to comp issues.

Questions..
303 is the only code it logged?
What’s the current mileage on it?
Also, was there any engine or trans work preformed prior to the code?