I bought a 2013 focus a couple of months ago, it's only done 55k genuine miles, full service history,I did about 800 miles then got the code p1263 and it ran rough, got the code cleared with a generic code reader and it's been running perfectly since, for around 500 miles up to now, is the injector knackered or is it just a random fail that's now ok?

The injectors on the 8v 1.6 TDCI were always weak.  I had 2 dodgy ones at 6 years/40k.  Plenty of others were replaced within the original 3 year warranty.

Very strange that yours ran rough but now runs fine though.  That seems more like a wiring fault.  

If you use Forscan you'll probably find Ford specific codes 'injector reached max learning limit' for one or more injectors, but generally you can just put up with them until they either cause rough running or fail MOT.  Personally I wouldn't replace injectors based on that particular code alone.

2 hours ago, TomsFocus said:

The injectors on the 8v 1.6 TDCI were always weak.  I had 2 dodgy ones at 6 years/40k.  Plenty of others were replaced within the original 3 year warranty.

Very strange that yours ran rough but now runs fine though.  That seems more like a wiring fault.  

If you use Forscan you'll probably find Ford specific codes 'injector reached max learning limit' for one or more injectors, but generally you can just put up with them until they either cause rough running or fail MOT.  Personally I wouldn't replace injectors based on that particular code alone.

It was running fine until the code flashed up on my way to work, ran rough to work wouldn't go above 35 mph, reset it at work with a generic obd that a colleague had, and it's been perfect since

10 hours ago, wiganfocus said:

It was running fine until the code flashed up on my way to work, ran rough to work wouldn't go above 35 mph, reset it at work with a generic obd that a colleague had, and it's been perfect since

Very strange.  I wouldn't replace the injector or wiring while it's running fine.  But would budget for repair in future.

As soon as I bought it I started running it exclusively on premium diesel and have not used any additives or injector cleaner etc, and I now have my own generic obd to keep in the car if it needs resetting on a journey, I suppose I will just have to see what happens over the next few weeks I do a 40 mile round trip to work everyday on mostly 50mph plus roads, so I suppose any problem will show itself soon enough, I just want it spot on, so if it goes again I will get sorted.

Archoil diesel additive rather than ongoing premium diesel may be worth looking into.
This site says the code is a wiring issue:
https://www.engine-codes.com/p1263_ford.html

17 hours ago, Shearers said:

Archoil diesel additive rather than ongoing premium diesel may be worth looking into.
This site says the code is a wiring issue:
https://www.engine-codes.com/p1263_ford.html

Thats vey helpful thanks, I will source a second hand loom in case it decides to pack in, as something to try before replacing an injector that has only done 55k. Is the loom easy enough to replace, I am fairly mechanical minded.

I'd give the wiring and injector and connectors (pin drag test?) a close physical inspection and then use a multimeter to check resistance on each injector whilst waggling the loom throughout to see if there is any break or resistance change. (it may mean finding the correct pins at the PCM)
Getting a loom may be overkill at this stage but if it's cheap enough you may want to go that route as a back up but it may not yet be necessary.
It depends how much of the loom has to be replaced up to the next connector.