Intermittent problem since changing fuel line 2006 fiesta 1.4tdci

Hi i’m hoping someone might be able to shed some light on the issue i’m having with my girlfriends diesel fiesta...

When I bought it the fuel line and primer pump needed replacing as the non return valve (probably wrong name) was knackered and it needed to be primed every day before starting. I bought the fuel line and primer pump and swapped it over for the old one. This was when the problem started.

When I get in the car first thing and start it up a “check engine/handbook” message comes up and the orange warning symbol that the handbook says is for “power train issue” this message however flicks off almost immediately. When you then set off driving, as the revs build, all of a sudden the message comes up, makes a beep noise and total power loss, this then stops and the revs build again and it happens again and again like this regardless of gear. as the car starts to warm up the power loss thing stops but the fault message continues to pop up and disappear, gradually getting less and less frequent the warmer the car gets. above the temp gauge reads about 60, the problem doesn’t re occur until the following time it’s started from cold.

Ive checked all the push fit pipe connectors are fully in and they are, ive even fitted a new fuel pump... 

does anybody have have any ideas what it could be? it’s doing my nut!!

thanks