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Charcoal Canister Purge

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi Guys,

Currently enjoying the Motorsport wiring course, just wanted some clarification. In the section 'Simple on/off switched' section in the wiring fundamentals, it was mentioned that the charcoal canister purge would be active at idle and cruise. Has this been your experience for all manufacturer types you've encountered? I'm confident that Ford Falcon B-series at least never used to purge the charcoal canister at idle due to the delicate balance of managing engine torque output vs engine component friction etc and the purge function had a minimum idle trigger point of roughly 1500rpm.

G'day Michael. I havent had any experience with the Falcon charcoal purge, but I can see the logic behind them not venting it at idle. My experience with purge systems is from older cars, late 90's stuff mainly :-).

Definitely dont want it active at idle, even if you are not worried about emissions, all those fuel vapours are going to upset your idle. I have heard some OEM's get quite complex in the purge strategy, taking into account fuel level in the tank, fuel temp, etc.

Here's how it works in Link ECU's just to give you an idea:

Thank-you for the additional information gents. Just finished the course, thoroughly enjoyed it Zac thank-you. Starting out small steps in my setup. I bought he plug and play haltech recently released for the Barra. Using these techniques to wire in the additional sensors. Thanks again.

As a general rule the newer the engine in terms of the regulation level it must meet (can't speak for Australia, only USA), the more intrusive the purging is from the factory and the more complicated the algorithm is to account for its effects. For our purposes, we're focused on making it a "normal" car that drives ok, doesn't have a funny fuel vapor smell, and doesn't have a check engine light if applicable.

Cheers Adam and Ray. PCLink documentation to the rescue once again!

I'm looking to set up the charcoal canister on an Audi 2.7T engine. I was just going to set it up on a PWM table map vs rpm but essentially under light load like posted by Adam. The plumbing on my engine goes pre-turbo for on boost and to the inlet manifold under vacuum. The fact it's plumbed to account for positive boost pressure means out of the factory makes me think I need to change what I was going to do. Looking for any advice on a strategy to control it.


From what I understand about your question you are asking if you can set the purge PWM map for light loads. But you also mention the plumbing on engine is intake manifold and pre turbo. Based on the plumbing description your vehicle is having capability for both purge under light loads and purge under high loads. I am expecting one more plumbing between post turbo and pre throttle, this is necessary for recirculation flow to allow vaccum at CPV during boost and hence allow purge at high load too. You may not need to configure vehicile for purge under light load only since it is capable for purge under high load as well.



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