I replaced the injector seals on my 2006 Fiesta 1.4 tdci two years and 14000 miles ago.

Now, after running perfectly all that time, one of them started chuffing.

I took the injector out to find the seals are knackered again!

Is this going to happen every two years or is there something I have done wrong?

Where did you get the seals from?

ebay

Wouldn't surprise me then that they haven't lasted. The cheap ebay stuff generally doesn't last, I've been there, done that. Bought a set of diaphragms for a carb I was doing up and they lasted hours before sagging straight away...

Sounds best then to get them changed. I changed the copper seals on my 1.6 TDCI along with the other seals / o rings. Hopefully they will be easy to take off as yours had been removed before. I don't do a lot of mileage possibly done 1000 miles since getting that done in January so can't give feed back on quality. 

what is esential is the face the copper washer sits against in the cylinder head is spotlessly clean, and obviously the the injector face. 

did you fit new injector clamp bolts and what torque?

I didn't fit new clamp bolts, I did the old ones up to 15lb ft as specified in my Haynes.

Why would they need renewing?

 

ford state bolts should be replaced and torqued to 15nm then another 70 degrees. 

Should the new black plastic O rings be a loose fit on the injector?

The O rings which the injectors sit on should be a tight fit. That bit that it covers has oil which flows through it so if its not tight or it fails you will see oil leaking out. This is my knowledge by the way when I changed them on the 1.6 TDCI so not sure if its different. 

The injectors on mine don't sit on O rings. They sit on copper washers?