as in title... it drives fine but as soon as it comes on boost it missfires, pops and bangs sometimes it boosts fine. ive changed the plugs then checked them after a drive and one of them goes a bit white on the end which i beleive is due to running lean and the rest are wet. anyone know what it could be?

 

...

 

just put petrol in the car and its boosting fine it seems like it starts to have this problem when it has 1/4 tank or less in... anyone know what it could be? maybe a fuel pump mounted wrong?

 

My old motor would do this if I ran anything less than 91 octane .. Strange about the 1/4 full thingy ... Gonna have to wait till it's back to 1/4 full mate.

 

is it properly mapped, AF ratio running as it should be etc?

 

its running on dta s40 mangement mapped by perfect touch in hoddesdon.

 

hi mate,
i have a focus RS, is it number 3 plug thats white?
what iunlet are you using? and what amount of boost are you running

 

which plugs and leads you running ?
try running the car on some rs focus plugs as they run slightly cooler than std zetec ones
would check leads and coil pack to for faults.
the car would benfit from running on super unleaded to cut the risk of melting something.
As for it doing it at half tank would check the pressure on the fuel pump and fuel reg as it could be just a earthing problem or the pump not man enough for the job
would also check to see if it is running right and have the set up checked

 

yes i also thought it could be faulty fuel pump, or the fuel pump is not man enough. could even be fuel filter?

 

if its doing iton 1/4 tank its just fuel surge,
need a swirl pot thats all

 

ahhh yes, i forgot about that

 

It will be the swirl pot as said above, the swirl pot keeps a reserve head of fuel for the fuel pump when the fuel level is low, typically less than 1/3rd of a tank.

 

Or could be the usual Walbro 255 problem when used to replace standard Ford intank pump. Has quite a high pickup as it has a built in filter. Well know issue for example on FRS - either never run less than 1/4 tank or, standard pump to external swirl pot or, use a 'blue' or 'green' top pump.

Martin