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Thread: How it works: Your Evaporative emissions canister!

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    Senior Member Ryephile's Avatar
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    How it works: Your Evaporative emissions canister!

    The fuel system in all modern gasoline cars consists of the following components:
    *fuel filler neck
    *fuel tank
    *vent tube between fuel tank and filler neck
    *activated charcoal canister
    *vent lines, a pressure sensor, and a vapor purge valve between the canister and the engine air intake
    *the combustion process of the engine

    The charcoal canisterís job is to absorb gasoline vapors from the fuel tank. It acts as a filter, similar to a Brita water filter on your kitchen sink faucet or an air filter for your engine. Itís designed to last the life of the car under normal operation. When its pressure gets high enough, the purge valve opens and the excess vapors are burnt in the engine via venting into the engine air intake. The ECU controls the venting and also alters the engine fueling to compensate for the vapors being added.

    There are three ways to damage your charcoal canister:
    1. Hit it with a sledgehammer or otherwise physically break it
    2. During refueling, keep topping off your gas tank until fuel spills into the vent line, flooding the charcoal canister with liquid gasoline and ruining the activated charcoal media
    3. Modify the Evaporative emissions lines to alter the flow characteristics of the vapors, restricting vapor flow and resulting in an over-pressurized and saturated canister, ruining the activated charcoal media

    The 3rd method is of particular interest to the 1.4L turbo MultiAir engine community, as Fiat/Chrysler has chosen an unorthodox method to purge the gas vapors into the air intake in the 500T, Abarth, and Dart 1.4T.

    The 1.4L turbo MultiAir is a bit of a strange engine. Its very small combustion chambers have unusually fast flame propagation, so itís able to run Stoichiometric for a large part of its load range while keeping EGTs nice and moderate. It also has the unfortunate saddling of being put in a car with relatively high total drag. As such, at normal Interstate speeds, it operates in boost rather than vacuum. At a steady 70 MPH, the engine needs to run approximately 3 PSIg just to maintain speed in an Abarth with factory 17Ē wheels & tires. This is unusual compared to larger engines, and it presents a couple problems that would otherwise go unnoticed to engine calibrators. The first is brake vacuum; thereís no longer a typical source for it at the intake manifold. As such, the engine has an accessory vacuum pump driven by the backside of the intake camshaft. The other is evaporative emissions purging, traditionally executed using engine vacuum. The solution Fiat/Chrysler implemented is unusual compared to other manufacturers; use a venturi and turbo boost to pull vapors from the charcoal canister into the turbo compressor inlet. This successfully facilitates purging the evaporative emissions vapors during normal engine operation.

    Like most engines, the engine computer commands vapor purge during wide-open throttle (WOT), or medium-high loads. This provides the least power delta when introducing gasoline vapors into the engine and creates the fewest headaches for the calibration engineers in obtaining smooth drivability and power output. Since the 1.4L turbo MultiAir is operating in boost during the normal purging regions of the load map, the gasoline vapors are purged into the turbo compressor inlet. This is the source of highest vacuum during commanded purge and allows efficient vapor evacuation from the charcoal canister. There is an added complication. If the charcoal canister is exposed to a surge in vapor pressure, it must be purged even during non-ideal driving conditions. This would be during low-load vacuum engine operation. To do this, there are two branches in the vent lines; the normal one going to the turbo compressor inlet, and the emergency purge line going to the intake manifold. The ECU is programmed to validate that both lines are able to purge at all times, and negatively altering either one will result in a posted Check Engine Light (CEL) with the appropriate code to indicate which line is compromised and in what manner.

    EvapPurge.jpg
    ^^This is a "cleaned up" datalog that shows during a 25 minute drive the engine operation when purge was commanded over 90%. To summarize, it's when the engine is running boost, and always when the throttle is full-open [during WOT and "de-throttled" mode]. I won't bore you here with vapor pressure plots, they're really boring.

    For the performance enthusiasts amongst us, the unusual evaporation purge technique employed by this engine creates a philosophical conundrum. The turbo boost used to pull vapors is actually a boost leak and compromises peak power along with inducing slightly erratic turbo response as the turbo has to fill both the intake system and the evap purge line. The loss of power has been circumstantially shown to be about 5 horsepower, enough for the sensitive posteriors amongst us to notice.

    There have been significant efforts put forth to fix the boost leak, with varying impacts on evaporative emission vapor purge flow. Next I'll describe the different methods in summary.



    Shagghie just sent me a nice picture that shows a generic modern engine emission system. It's helpful though not Abarth specific, just for reference.
    Shagghie_pic.jpg

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    Senior Member Ryephile's Avatar
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    Quote Originally Posted by fidgell View Post
    This is very interesting. I dont fully understand the differences between the Boomba, Ryans and this solution. Who couldnt want "free horsepower", ill try reading the acres of info again as it seems im in a minority who isnt doing this. I guess if its engine safe it cant hurt....
    A great question!


    We've seen 4 methods come to light. They all provide the same ~5HP gain over stock, but do so with varying impacts to the evaporative emission system.

    *"Free HP Mod" that ATM developed on the Dart forum and then was brought over here. This puts a check valve [Boomba-brand or otherwise] on the "boost leak line" feeding the venturi T. Curiously enough, the check valve is used to only block the boost. Since it's tied to a venturi, the vapors purged during emergency purge operation take the path of least resistance, which is the emergency purge line connected to the intake manifold just downstream of the throttle body. The boost leak line never purges vapors into the charge pipe. You can remove this line and cap it and achieve identical functionality. The main negative of this solution is it negates the functionality of the venturi T and does not allow for efficient canister vapor purge. It may cause long-term charcoal canister saturation damage, however the emergency purge line to the intake manifold should keep the canister from being ruined.

    *Dart1.4t, myself, Chris the Admin, and Musicsurf have all collaborated to put together my Evap re-route setup. This still caps the boost leak, but takes it to the next level by improving the vapor purge line efficiency in lieu of the venturi T being removed. It does this by replacing the convoluted stock lines with a streamlined and aerodynamically conscious approach. Of the hours of boring vapor pressure plots I have, I discovered this method actually purges the canister more efficiently than the stock configuration. It's critical to keep large evap lines and a "Y" fitting, "T" fittings add restriction and won't allow the same purge efficiency.

    *Tork just released their solution. It appears to be a derivation of my setup, however they have chosen to purge the evap vapors to the atmosphere. This certainly makes aftermarket intakes much easier to implement, but the downsides are gasoline vapors are vented into the atmosphere and not plumbed back into the intake when the ECU is expecting it, so drivabiilty during commanded purge may be slightly rougher.

    *Hi-Performance Store has a catalog item they call The Boost Retainer Valve. This puts a solenoid in-series with the boost leak line, and keeps it open until a certain boost level is achieved. The boost threshold when the solenoid actuates is not disclosed, however if it's high enough, it will allow vapor purge during typical Interstate driving, but never at WOT. This is a slightly better solution than simply plugging the boost leak, but not as effective at maintaining the health of the charcoal canister as the Tork or my re-route solution.

    Two out of the four solutions are tied to for-profit businesses, so they have a vested interest in making sure my facts are accurate [for both positives and negatives]. If you as a consumer want a kit to buy and don't want to DIY, my advice is to buy the Tork kit and "finish the job" by plumbing the vapor purge line back into the turbo compressor inlet. As it stands right now, the two very best all-around solutions are keeping the car stock or taking the initiative to do my re-route solution as a DIY.

    I hope this helps,
    Ryan
    Last edited by Ryephile; 12-05-2013 at 05:07 PM.

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    Member Dukes2004's Avatar
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    Something I found that I am sure is an isolated mistake. When I went to follow your guide for the reroute, which I haven't attempted yet, I noticed that my venturi T was actually cracked on the left hand side! I had been noticed boost fluctuation but never saw a CEL. I replaced the line with some high quality lines and a T fitting for now, and the car is much smoother. Definitely am going to be looking into these options over the weekend. I already have all the parts for your method.
    2013 Nero Abarth

    Modifications: H&R springs, 35% tint, red dash panels, custom Abarth shift knob, red head rest inserts, Madness Intake.

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    MODs recommend making this a sticky in Abarth Performance section please...easy to find and paste in threads when this comes up in future...
    Rye... THANK YOU... this is wonderful.
    http://www.fiat500usaforum.com/image.php?type=sigpic&userid=509&dateline=14328366  62
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    Senior Member ABARTH TAMER's Avatar
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    Thanks Ryephile, excellent post. Long, but interesting enough where my eyes didn't glaze over.

    I can't imagine anyone (especially in Ca.) ruining or venting their canister. The complications during emission testing, and living in So. Cal with air quality, would not be worth it for me. One evap canister here, one cat there, it all makes a difference here under the dome in So. Cal.

    Good to hear objectives can be achieved, with no downside.
    Last edited by ABARTH TAMER; 12-05-2013 at 06:32 PM.

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    Great write up (although I must admit that my brain hurts now)

    Thanks again!

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    Super Moderator Tweak's Avatar
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    Quote Originally Posted by shagghie View Post
    MODs recommend making this a sticky in Abarth Performance section please...easy to find and paste in threads when this comes up in future...
    Rye... THANK YOU... this is wonderful.
    Easy enough and since it is useful it merits being stuck to lessen the search for it and the questions or issues down the road. Thanks for taking the time Rye.

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    Senior Member trevc's Avatar
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    Thank you for taking the time to explain the system so clearly. It actually made sense to me!

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    Senior Member msjulie33's Avatar
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    Thanks, appreciate the details of the Abarth's "unique" routing - my question, maybe to Chris (admin) but more specifically to Fiat engineers - we know you check out these forums.

    Anyway to get some feedback here? I'd be curious to hear the explanations for why the car comes the way it does when the reroute design appears simpler if it had been done in that fashion from the start. Perhaps it's a belief that there is no drivability issue - extra power is always nice but for sure the part throttle response could be smoother...

    Back when I had my Audi, the diverter valve stock was woefully inadequate for the boost potential on the newer car and resulted in similar part throttle power loss/surging/etc. (it was essentially the same thing in that the valve "leaked" boost because it opened too easily and worse, sometimes the diaphragm actually just ripped and it failed altogether). Took 3 years for them to upgrade their part I think; external vendors had great options in just some months I think...

    Anyway curious ...
    Wicked Dot - Rosso+black Abarth 500c
    MoJo - Electric Orange 500e stealth performer - lease over, replaced with a faster! E

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    Senior Member Ryephile's Avatar
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    Quote Originally Posted by msjulie33 View Post
    Thanks, appreciate the details of the Abarth's "unique" routing - my question, maybe to Chris (admin) but more specifically to Fiat engineers - we know you check out these forums.

    Anyway to get some feedback here? I'd be curious to hear the explanations for why the car comes the way it does when the reroute design appears simpler if it had been done in that fashion from the start. Perhaps it's a belief that there is no drivability issue - extra power is always nice but for sure the part throttle response could be smoother... ...
    It's unlikely Fiat will ever make a formal announcement for a non-safety critical "niggle", but perhaps through the grapevine some details can come to light "off the record". Based on the conversations I've had with friends at Chrysler, it's something to the effect of "the intern probably did it". This happens all the time in the automotive OEM world. Somebody makes a fairly abstract decision without using or knowing about the generations of wisdom learned at the company and aspects of the car aren't as good as they can be. It's very easy to make a big list of recent cars with obvious engineering compromises: R53 MINI "yo-yo" bypass valve vacuum routing, VAG diverter valve, R56 MINI timing chain, BMW HPFP, VW CR TDI HPFP, almost everything on the Mk4 VW's, our 500's strut mounts, NA Miata short nose crank, Lotus Elise oil cooler lines, the mountain of boring cars with big laundry lists of recalls for fires, wiring harnesses, more fires, faulty airbags, airbags that go off for no reason, etc..

    What happened in this situation is the hard parts were already designed and paid for, and the calibration engineers had to tune the ECU to make it work as best as possible and still meet emissions and launch deadlines.

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