i had my 1.4 tdi serviced and some repairs done by a mobile engineer...very good chap

he asked when my fuel filter needed done which didnt need done at the time

i told him i had renewed it a while back and not for another year or two...4 years between changes

he asked did i prime the new one i did  with fuel before reconnecting the hoses...which i didnt

did it start ok?

yes no problems..!

he was telling me that an air lock can occur and i should have ran the little pump in the tank to prime it..he can do that through his diagnostic tools

how could i do this priming myself, or does one have to pour diesel into the filter by hand etc and then reconnect the tubing

he said starting the engine without the filter being primed can lead to problems...which i luckily escaped

cheers

geof

 

I've changed many VAG diesel fuel filters without priming the system afterwards.

 

As long as you're careful and ensure as much diesel fuel remains in the fuel filter housing as possible then you'll be fine. Take it slow and steady to minimise the chances of introducing air into the system.

 

I ensure all of the fuel in the old filter is allowed to drip back into the fuel filter housing before fully removing it. Some even top the fuel filter housing up with fresh fuel after inserting the new filter.

 

Cycling the ignition a few times used to do the same job as priming the pump using diagnostics, but the later common rail (CR) engines don't automatically prime the fuel pump on the ignition, hence the recommendation to purge the system using a diagnostic tool such as VCDS.

 

 

 

 

 

 

 

 

 

Edited 9 June, 20206 yr by silver1011

brilliant answer and coverage with photos

 

mine is the type where the filter comes with a new casing complete and one takes the old one out and drops the new one in and pushes back on the tubing.

so i can see that mine needs to be primed by the fuel pump in the tank then the tubing to the engine fitted pronto...!!

its a PD engine if that makes any difference and a 2008 1.4TDi model fabia

 

i may try using the ignition switch as you pointed out...any advice on how to stop too much coming through if i am doing it alone?

 

cheers

geof

 

 

On a PD engine, it doesn't really matter so much, after the lift pump is the tandem pump and it is still only a low pressure pump (10BAR) so a bit of air through the lines probably wouldn't cause any damage to it.

 

If you want to prime it for an extended time, if you put 2 spade crimps on a piece of wire you can just short out the relay base and this will put power to the lift pump.

 

Common rail engines are a completely different story as there is sometimes another auxiliary fuel pump between the fuel filter and the HPFP which should be run as well as the lift pump to prime all the lines. If you follow the advice above you will likely have no problems but if you end up with an airlock in the system and have to crank for a long time with no fuel then excessive wear can occur to the HPFP and if that grenades say goodbye to your injectors as well.

 

 

 

 

thanks...the short out should be easy i have several crocodile clips and fine wire which i could use..??

 

where might i find the relay for the lift pump??...its the one in the tank which whirrs a bit when putting on the ignition??

 

many thanks

geof