Cylinder Misfire on cylinder 3 (2015 XLT V8)

[effingpot]

Hi again from the UK! My check engine light came on a few week ago and we got a misfire on cylinder 3 (PO303) so I got some spark plugs sent over from the US and after a week it came back on again. So I got some coils sent over and replaced all them, but same problem. The car is in my local garage today for another thing but the guy is gonna see if he can work out what's going on. We don't have Expeditions here (apart from mine and few others) so any tips are welcome. I have looked at the other posts on similar subjects and we will see if the injector looks ok, maybe swap it with another one to see if the fault moves cylinders but the garage owner has never seen an Expedition before, hence the question.

Also - the PO300 warning may suggest something else? Not sure!

I'll pass on any tip you may have.
Thanks in advance.

 

[effingpot]

OK bit of an update. The check engine light seems to point at misfiring on Cyclinder 3. All the spark plugs were replaced in Feb 2024, the coils were replaced. Same problem. The injectors were cleaned, same problem. The plugs, injectors and coils were all swapped with Cyl 1 but the problem stayed on Cyl 3. The pressure on Cyl 3 is just 10psi lower than the others and well above 100 so that should not be a problem.
Still getting the problem and not sure what to try next.
Any suggestions welcome.
Thanks

 

[Yupster Dog]

Whenever it is cylinder 3 or 4 make sure you check the heater hoses and the T connectors for leaking.
Sometimes it wont leak unless it has pressure on it, so make sure you look when it is hot or do a pressure test on your coolant system.

 

[effingpot]

Well finally we seem to be sorted. Quick summary in case the same happens to you. The fix was to replace the injectors (not just clean them). Though to do that was hard as the injectors I got from Rock Auto were not really compatible and delivered too much fuel, starting the engine was hard, plus some new error codes. So I took the numbers off the old ones and found some in Cyprus of all places. So new injectors, new plugs, new coils and we're back in business. Thanks for the various pointers! Love my Expy!