on the esc cossies how exactly does the carbon cannister work? i assume the fumes from the fuel tank are passed through this,neutralised then the solenoid opens and they are sucked back into the engine but what determines when the solenoid opens and for how long etc?also what is the valve that is connected up by the fuel filler pipe in the rear wheel arch for?always wondered and thought it was about time i found out,sure someone will know?

 

This is for the small turbo Escort Cosworth, I expect the large turbo is a little simpler.

The carbon canister acts a reservoir for the fuel vapours that are only allowed into the inlet manifold if certain conditions are met. The process for deciding purge solenoid dutycycle is;

The ECT has to be below 123.33 deg C.
Certain 'ECT at start' vs ECT and 'time since up to temp' vs 'time since start' criteria have to be met
Decide if purge at closed throttle is allowed (it is in the stock ecu)
The ecu has to be in closed loop operation (it can be calibrated to also do the purge in open loop)
Calculate purge solenoid dutycycle based upon airmass entering the engine (this varies from 4.69% at 384 kg/hr to 100% at 691 kg/hr)
Alter the purge dutycycle according to two purge timer values
Average the new dutycycle with the old dutycycle to prevent too large a change
Alter the purge dutycycle according to adaptive learning stored values.

As can be seen, quite a few decisions are made to calculate how much fuel vapour can be added without detrimental effect to the running of the engine.

Oh yeah, the valve near the filler is just a one way vent to allow air into the tank to compensate for the fuel used.

 

cheers for that its not simple then how do you know if its working then,what would happen if it packed up?

 

If the solenoid failed in the closed position then I don't imagine there will be any problem (I'm not sure if the injector pulsewidth is reduced to compensate for fuel vapour) until the canister cannot hold any more vapour. I guess once the canister is full then you'll get a smell of petrol from the tank or canister.

If the solenoid failed in the open position then the fuel vapour will constantly be venting into the inlet manifold and the short term fuel trims will recognise a rich condition and lean off the desired AF ratio to suit.

 

MY SMALL TURBO SMELLS OF FUEL OCCASIONALY ALTHOUGH IT DOESNT LEAK FUEL DO YOU NO WHERE THE CARBON CANISTER IS FITTED TO THE SMALL TURBO CARS

 

It's in the drivers wheel arch behind the plastic lining.

 

where does the ttank breathe from then?if theres a one way valve like u say to let air in,where does it let it out for expansion purposes?

 

Into the carbon canister.

 

so if it wasnt working then the tank wouldnt be able to breathe?

 

I think there's no such such thing as the carbon canister 'not working', it's simply able to absorb the vapours or it's saturated and cannot absorb any more (someone shout out if I'm wrong). If the canister is saturated then I think this is when you'll be able to smell petrol fumes as the canister or tank will leak vapour.