Purge valve operation

[else]

Hi All,

Anybody know how the purge valve works, especially when it is energised?

I have fitted a Motec ECU and i am not sure when or how often to power the purge valve to clear the hydrocarbons from the canister.

Any help or advice would be gratefully received

Andy

[chassis 33]

I believe on the standard hotwire setup the purge valve is opened at wide throttle angles (ie towards full) at engine speeds greater than 3000rpm. Any more than that I couldn't help you with sorry.

Regards
Iain

[else]

Bugger,

Thats an awkward one to reproduce Iain. I'll have to think of a way round that.

Andy

[spend]

I reckon that is the MA quoted operation. I have read somewhere that it opens much more often ~ if you never use full throttle it would never purge ~ so this may have been for lazy Landies?

If you can program it as a one off just first time you hit 3000-3500 would be fine maybe.

Dave

[else]

spend said:

I reckon that is the MA quoted operation. I have read somewhere that it opens much more often ~ if you never use full throttle it would never purge ~ so this may have been for lazy Landies?

If you can program it as a one off just first time you hit 3000-3500 would be fine maybe.

Dave

Dave,

I haven't got any spare outputs on the ECU to use, so the solution has got to come from a more "mechanical" method.

Andy

[spend]

So where are you going to mount the switch then?

Dave

[Cider Andy]

else said:

I haven't got any spare outputs on the ECU to use, so the solution has got to come from a more "mechanical" method.

What do all the other outputs do? Could you wire it to one of them?

[else]

spend said:

So where are you going to mount the switch then?

Dave

Yeah, quite. I think i may just rip it out and go back to the traditional fuel tank breather to atmosphere.

Unless anybody has any better ideas? (i could be leaving myself open for all sorts of comments now but hey ho!)

Andy

[andy-w]

i was thinking along those lines as well....i noticed that the hose going to the carbon can had touched the exhaust and had a hole burnt through it.

The car ran fine so i cant see the carbon canister having any adverse effects on the running....?

[spend]

I think its one of these issues like precats, they are only legislated for at time of manufacture.....

Dave

[miketvr]

I did some experimentation with a sophisticated Lucas analyser at the end of last summer. The analyser showed that the purge valve was operated in sympathy with road speed less or greater than 3mph. I have a '94 Chim so can't vouch for later models, but it seems logical to me.

On the Chim ('94 on) there is a speed converter which puts a square wave signal into the ECU at constant rate when the road wheels exceed 3mph or thereabouts. Therefore when the ECU senses that the car is moving, which also means that there is air flow around the car which will prevent any dangerous build up of petrol fumes in the bodywork around the purge pot.

Mike

[spend]

miketvr said:

Therefore when the ECU senses that the car is moving, which also means that there is air flow around the car which will prevent any dangerous build up of petrol fumes in the bodywork around the purge pot.

I dont understand that at all, am I missing something?

Dave

[That Daddy]

Andrew i would just vent to atmosphere,i mean older cars and bikes are like this so dont feel bad about the astmospheric thing,i think you will be just adding to your work,its something you can come back to later.

[GreenV8S]

spend said:

miketvr said:

Therefore when the ECU senses that the car is moving, which also means that there is air flow around the car which will prevent any dangerous build up of petrol fumes in the bodywork around the purge pot.

I dont understand that at all, am I missing something?

Dave

I don't understand it either. Conventionally, the carbon cannister is fitted in line with the fuel tank vent pipe and the purge valve sucks fresh air into the engine via the carbon cannister. There's no way for the purge valve to release petrol fumes outside the engine.