2014 C3 picasso 1.6 hdi injector issue

[Coded]

Good day.

I've had an injector issue on my C3 picasso for about 8 months. Originally the injector issue arose due to the car not being used (it's a 2014 with 37k on the clock)
I originally bought an injector from euro car parts which seemed to already be faulty (I don't know if it was a recon one or not) I took my car to citroen to get the injector coded and they said it was faulty. I told them just to code it and give the car back as I know they would have pulled my pants down wanting to change all 4 injectors. I continued to drive the car as it was still drivable and was only slightly stuttering in 6th low revs. I decided to tackle it again and took all 4 injectors out and took them to an injector specialist which cleaned and tested all 4 injectors and told me one was faulty. I purchased a brand new injector from them and fitted it and also bought diagbox so I could code it in myself.
Originally when I put the injector in i took it for a drive and the engine had quite a bad knock noise and an error code saying the injector was overfuelling and could be stuck open (this error code referring to the brand new injector I just installed. I wanted to cry) I decided to switch the injector from cylinder 4 to 1 (recoded to the new positions) to see if the error code followed the injector but now I don't get any error codes at all. The car drives beautifully, no more stuttering, pulls lovely in every gear and the mpg has risen massively (got almost 70mpg driving from Portsmouth to London) which is the most I've ever got. BUT..... I still have an engine knock. I'm completely stumped over what could be causing it. I originally wondered if I have torqued the injectors up enough as the only torque settings I could find online was 4nm and 65 degrees which I did to the best of my ability. Does anyone know if these torque settings are correct? Or possibly know what else I could try to stop the knocking? It surprises me how lovely the car drives now whilst sounding so bad.

Sorry for the long essay I just wanted to give as much information as I possibly could.

I have the car booked in to go to citroen again tomorrow but I'm not going to turn up. Diagbox was expensive and feel with your guys expertise I may be able to conquer it. My dad gave me the car just before he passed away so doing absolutely everything I can to get it running perfectly again.

Really appreciate any help you guys can give. I wish I thought about joining this forum sooner. This injector issue has been a thorn in my side for too long.

Thanks chaps.

[PaulC5]

I cannot help but point out that Citroen sometimes number cylinders from the gear box end, in case you did not know.

[Coded]

Yeah mine are numbered starting from 4 looking into the bay. Figured that out the hard way a long time ago.