MPG and charcoal canister

[Rustam]

I've looked into threads that talked about charcoal canister and found an allusion that it may be responsible for poor MPG. For some while now I've been trying to improve the performance - but no success... Everything has been changed besides charcoal canister. Wires, distributor, injectors, fuel regulator, etc... Good compression.
Does someone have experience with the effect of charcoal canister on MPG?

[genphreak]

I've looked into threads that talked about charcoal canister and found an allusion that it may be responsible for poor MPG. For some while now I've been trying to improve the performance - but no success... Everything has been changed besides charcoal canister. Wires, distributor, injectors, fuel regulator, etc... Good compression.
Does someone have experience with the effect of charcoal canister on MPG?Sounds like a gaseous illusion to me. Why would it do this, waht did this source say- and who was it? Tho you might know this already- your probs are likley to be AFM, ICV, intake leaks or worn valves/rings, in that order.

[Rustam]

Sounds like a gaseous illusion to me. Why would it do this, waht did this source say- and who was it? Tho you might know this already- your probs are likley to be AFM, ICV, intake leaks or worn valves/rings, in that order.

Someone said in the threads that "bavauto.com" states that bad charcoal canister can affect MPG...

What is ICV?

[pingu]

ICV is the Idle Control Valve.

[Rustam]

Sounds like a gaseous illusion to me. Why would it do this, waht did this source say- and who was it? Tho you might know this already- your probs are likley to be AFM, ICV, intake leaks or worn valves/rings, in that order.

How can bad ICV affect MPG?

[ThoreauHD]

What the hell is a charcoal canister?

[Rustam]

What the hell is a charcoal canister?

Charcoal canister is used to collect gas fumes from the tank - to reduce pollution.

[ThoreauHD]

I'm not familiar with that but my mpg and efficiency increased with an 02 sensor replacement and spark plug/ignition coil replacement. And if you have a intake manifold/head gasket vacuum leak- that would be the first place to start.

Found a write up on the charcoal canister:

Do you know how the system works? What it does is take the gas vapor from when the gas heats up or is poured into the tank and then condenses it and inserts it into the intake. This makes for a wet manifold as well as non-metered air entering the intake. This system was a complete after-thought from BMW and all true Euro cars don't have it. The reason why is because the US EPA wanted to prevent the gas vapors from escaping to the atmosphere. What really they are doing is creating a situation where you are getting extra air and fuel vapor into the combustion. As you will know, gas vapor does not combust as easily as liquid, and in fact is very hard to combust, and is therefore put through the cat and out the tail pipe. This increase the emissions of the car and also robs power because of the wet manifold condition and the increase in un-metered air going into the motor.

After completely understand how this system works and what it does to the operation of the motor, you will see that it has no benifit and in fact the claim you made of having your premium evaporting should happen because of the way the system works in the European cars where the expansion tank is vented to the atomsphere. What expansion tank does in European car is that it acts as a collector for the gas vapor and then once the gas vapor converts back to liquid, it flows back into the tank. This is also shown by the placement of the expansion tank in the car. The expansion tank is placed higher than the main tank and is also far away from a hot exhaust. This allows the gas vapors to cool and therefore condense back into a liquid and flow back into the tank. Thw only reason why there is a line to the outside of the car is that in cases when you are filling up the car, you are inputing more gas than air can come out. This therefore allows for the pressure in the tank to be released and so you are able to fully fill the tank. I have had this happen on a 7-series where I was filling it up and the pump stopped, but the tank was not full. This was caused by the charcoal canister system and the fact that it doesn't allow pressure to be released from the main tank quickly in situations like filling the car. Also, the possitioning of the line port on the expansion tank that runs to the charcoal canister is also at the top of the tank. If you know about chemistry, the gas vapor will settle to the bottom of the tank because of the fact that it is heavier than the normal air. Therefore, the normal air will go out of the expansion tank, and the fuel vapor will stay in. Now you are correct in saying that when you fill the car it will smell like gas for a little bit, but you are incorrect in saying that you want positive pressure in the gas tank. While positive pressure will allow for the tranfer pump to work easier, you will not be able to fill the car fully after driving. Also the charcoal canister system does not keep positive pressure in the tank. If you have ever looked at the canister and how it works, it is open to the air on the underside. This allows for the prevention of a build-up of pressure in the tank, but it doesn't work very well.

In closing, the charcoal canister system was an after-thought by BMW to abide by the EPA laws. Personally, after reviewing how the system and the problems that it cause, such as rough idle, incorrect mixture, poor emissions and difficulty in filling, I see no reason to keep the system on the car unless it is required by the emissions laws in your state.

So in effect if it ain't working, it don't matter.

[Rustam]

I'm not familiar with that but my mpg and efficiency increased with an 02 sensor replacement and spark plug/ignition coil replacement. And if you have a intake manifold/head gasket vacuum leak- that would be the first place to start.

Found a write up on the charcoal canister:


Well, O2 is brand-new from last year, spark plugs and the coil are ok... I guess by "head gasket leak" you mean "valve cover gasket leak"? I changed the gasket last summer - everything seemed ok - I am a bit puzzle by what you mean.

Where did you find the write up? I am planning to upgrade the charcoal canister so that the mixture is unaffected by it. I will create new page on my website.

The write up is very right on the effect on idle by the charcoal canister. Two nights ago I disconnected the purge valve that lets the fumes from the canister into the intake. The result - rock steady idle that I had never seen in my car. Defied Bruno's statement that the idlling performance on m30 is inherently bad. The ability to suck in unmeasured air through charcoal canister is often overlooked incidentally because of no idea what this canister does to begin with.

It's interesting to note that the air gets to be sucked in so much that it is possile to get resonance from the charcoal canister while adjusting the mixture. Apparently leaner mixture can induce relatively high pitched whine from it.

[Russell]

Charcoal canister change is recommend by Bavauto every 120,000-150,000 or so miles. I understand if it clogs it will reduce gas mileage. If clogged you might smell gas fumes. Also, if you are in the habit of topping off your gas tank, it can send raw gas and not fumes to the canister.

I replaced mine with no change in in gas mileage. Even so, you might want to recheck all the rubber hosing associated with the canister/blow-by/PCV like operation for vacumn leaks.

[joshua43214]

I would like to respectfuly make a few corrections.

Liquid gasoline does not burn, only the vapor burns. You can drop a lit match in a glass of gasoline if you would like to verify this.

The fuel in the tank is being constantly agitated by the fuel return causing increased evaporation, this combined with filling the tank and fuel heating creates a very high amount of fuel vapor. The expansion tank above the fuel tank(its on north american cars too) separates the vapor allowing to condense back into the tank. The excess vapor is traped by the carbon filter. Liquid fuel should never reach the expansion tank, let alone the carbon canister unless you improperly fill the fuel tank. When the purge valve opens, fuel vapor is allowed to enter the intake. The purge valve should only operate under certain situations such as starting so as not to interfere with normal fuel management, and since the DME operates the purge, it will make the proper compensations when it is open.

Proper operation of the carbon canister actualy improves cold start and WOT response since it allows pre vaporized fuel to mix with the incoming air. The carbon canister is a part that does over time need to be replaced, if you smell fuel around the car after a fill up, or after it has sat in the sun for a few hours, it means that the carbon has become saturated and is no longer able to absorb vapor.

It is true that removing the system when it has failed will sometimes improve things such as idle quality. But the car will be happier if the system is running properly, especialy on cold mornings.

[Rustam]

Charcoal canister change is recommend by Bavauto every 120,000-150,000 or so miles. I understand if it clogs it will reduce gas mileage. If clogged you might smell gas fumes. Also, if you are in the habit of topping off your gas tank, it can send raw gas and not fumes to the canister.

I replaced mine with no change in in gas mileage. Even so, you might want to recheck all the rubber hosing associated with the canister/blow-by/PCV like operation for vacumn leaks.

Thank you, Russell.

[Rustam]

I would like to respectfuly make a few corrections.

Liquid gasoline does not burn, only the vapor burns. You can drop a lit match in a glass of gasoline if you would like to verify this.

The fuel in the tank is being constantly agitated by the fuel return causing increased evaporation, this combined with filling the tank and fuel heating creates a very high amount of fuel vapor. The expansion tank above the fuel tank(its on north american cars too) separates the vapor allowing to condense back into the tank. The excess vapor is traped by the carbon filter. Liquid fuel should never reach the expansion tank, let alone the carbon canister unless you improperly fill the fuel tank. When the purge valve opens, fuel vapor is allowed to enter the intake. The purge valve should only operate under certain situations such as starting so as not to interfere with normal fuel management, and since the DME operates the purge, it will make the proper compensations when it is open.

Proper operation of the carbon canister actualy improves cold start and WOT response since it allows pre vaporized fuel to mix with the incoming air. The carbon canister is a part that does over time need to be replaced, if you smell fuel around the car after a fill up, or after it has sat in the sun for a few hours, it means that the carbon has become saturated and is no longer able to absorb vapor.

It is true that removing the system when it has failed will sometimes improve things such as idle quality. But the car will be happier if the system is running properly, especialy on cold mornings.

I agree with the statements here, especially the first one. The write up was a bit rubbish, especially on the point of gas vapors not "burning". I feel that the fumes provide smoother operation - they provide faster ignition, and I am looking forward to keeping the system in the car.

[MSM]

Re: "This system was a complete after-thought from BMW and all true Euro cars don't have it. The reason why is because the US EPA wanted to prevent the gas vapors from escaping to the atmosphere."

For what it's worth, my "true Euro car", and, according to the bmw parts database, all other european 535i cars do have the evaporative emissions control system as standard. It's not an afterthought slapped on to US cars only.

[Alexlind123]

Bump. Im interested in this topic...

[joshua43214]

Bump. Im interested in this topic...

What more would you like to know?

[ryan roopnarine]

i'm curious as to why the writeup author would say something like "fuel vapor doesn't burn" that's the whole point of a fuel injector or carburator, to get the liquid as close to as an ideal gas as it reasonably get. solubility of gases DECREASES in liquid, not sure how the oxygen/charge mess would work if one were trying to shoot liquid gas into one's engine.

[Rustam]

What more would you like to know?

well, I believe I have more...

The evaporative purge valve was stuck open in my car as I have found out as a result of simple curiosity of its condition. Tried to blow through - it went - so I figured that it was "stuck open" contrary to its natural state "shut closed".

So I tried to pry open the two halves of the valve to peek inside to see whether I can revive the valve. Upon application of 12V potential at its contacts before opening no reaction occured.

The valve is very simple to revive - apparently pieces of charcoal had blocked the petal that closed the opening making it unable to move.

Now important note - natural state of this valve is "open". Upon application of voltage to the contacts the petal crossing the diameter gets magnetically attracted to the opening leading towards the manifold shutting it closed. Once attracted, the negative pressure of the manifold aids at the shot closed state.

So some money is saved (~$60?) - now the valve operates and does it quite well... I'll update my website with this information soon.

____________

I'll put it back in my car tomorrow maybe it will give me 300 horsepower...

[Alexlind123]

Not quite the same, but have you ever burned flour? Its really kind of coool actually.

[MSM]

"The valve is very simple to revive - apparently pieces of charcoal had blocked the petal that closed the opening making it unable to move."

I guess it might be worth changing the charcoal canister too, or at least fitting an appropriate inline filter, if the media is trying to get itself injested by the motor. :)

[Rustam]

"The valve is very simple to revive - apparently pieces of charcoal had blocked the petal that closed the opening making it unable to move."

I guess it might be worth changing the charcoal canister too, or at least fitting an appropriate inline filter, if the media is trying to get itself injested by the motor. :)

You guess same way as I do - I will get the canister, and think about filtering still...

[Morgenster]

Bump...

So does anyone have a schematic on where to find this stuff on an M50 engine? My idle is giving me the same symptoms as described earlier and I get a lot of gasoline smell in my car without any apparent leaks (when cold in standstill or at slow speeds).
ICV seems to operate normally since idle will almost always level out at some 600 RPM.
Also, how hazardous would it be to work on this thing, cuz it is still fuel related?

[Alexlind123]

Bump...

So does anyone have a schematic on where to find this stuff on an M50 engine? My idle is giving me the same symptoms as described earlier and I get a lot of gasoline smell in my car without any apparent leaks (when cold in standstill or at slow speeds).
ICV seems to operate normally since idle will almost always level out at some 600 RPM.
Also, how hazardous would it be to work on this thing, cuz it is still fuel related?

Im pretty sure the EVAP system is not under pressure. It does contain fuel annd vapors though, so dont smoke when youre working on it.

[Morgenster]

Im pretty sure the EVAP system is not under pressure. It does contain fuel annd vapors though, so dont smoke when youre working on it.

Cool, but I still can't find it. It's a Euro car, but my M40 engine on the e30 had it, so I guess this one should also.

[Rustam]

Cool, but I still can't find it. It's a Euro car, but my M40 engine on the e30 had it, so I guess this one should also.

You can try using realoem.com to see "exploded views" of your setup.

[Rustam]

Bump...

So does anyone have a schematic on where to find this stuff on an M50 engine? My idle is giving me the same symptoms as described earlier and I get a lot of gasoline smell in my car without any apparent leaks (when cold in standstill or at slow speeds).
ICV seems to operate normally since idle will almost always level out at some 600 RPM.
Also, how hazardous would it be to work on this thing, cuz it is still fuel related?

Shogun posted a message with a picture of V12 compartment with the canister mounted within immediate proximity of exhaust manifold. Perhaps it is not hazardous to work with it at all?

[genphreak]

Good work Rustam. So if one suspects poor economy, poor power, go pull the purge valve and clean or replace? I've had this problem (suspected vacuum leak for a very long time)

I am sure I need to replace the Charcoal canister in my car, am tempted to buy a new valve and canister and be done with it. Have you done yours yet? How much was it and where is best to get it? Anyone else doing it? Here we go again, I have to buy (another item) from the US again... :p

- is the valve you opened up easily cleaned without destruction? (ie I'm awaiting your write up!)

EDIT; As you called it a purge valve Rustam I got confused. Somehow couldn't find any such sucker on realoem so ended up thinking this must somehow be the fuel tank purge valve (non-return valve) instead, which is in the tank. Doh! feeling a bit woozy as it is right there staring me in the face: This is the sucker we're on about: Item 1.
FUEL TANK BREATHER VALVE AB-ELEKTRONIK1 13901726705
http://www.realoem.com/bmw/diagrams/g/o/4.png

Not the purge valve (12) in the fuel sender...
http://www.realoem.com/bmw/diagrams/i/e/6.png
12 NON-RETURN VALVE 116141179282

[genphreak]

I am glad that article going on about the emissions system being an afterthought is discredited finally. Good work Rustam, Joshua.

I came accross it years ago and apart from sounding like the usual dude harping on about something he doesn't quite understand (as there is an ECU in there controlling stuff). It was no surprise to find he concludes it is a crap system as it all worked so much better when it was bypassed.

There is no way BMW would take a bodgey approach to this, even all those years ago. One only has to look at the effort they spend building market leading engine management systems to know the author was on speed and way past the turn-off.

[Russell]

I replaced my canister with no change in in gas mileage. No big changes for about 50,000 miles. Even so, you might want to recheck all the rubber hosing associated with the canister/blow-by/PCV like operation for vacumn leaks.

I got miy canister from BMA in California for about $40 US. I think the small valve near the canister was about the same price. I have not cleaned or recheck it.

[Morgenster]

Found it!

So: euro M50's have it as well. The whole 'afterthought' theory is bs.
On my M50 E34 the canister is actually located in the far left front corner of the engine compartment right next to the headlights.
The valve is located right behind the air intake box housing the air filter.
Will check soon to see if this thing needs work.

[Russell]

E34 525i FUEL TANK BREATH.VALVE/DISTURB.AIR VALVE</B>
RealOEM.com Home (http://www.realoem.com/bmw/) => Select another car (http://www.realoem.com/bmw/select.do) => FUEL PREPARATION SYSTEM (http://www.realoem.com/bmw/partgrp.do?model=HD63&mospid=47404&hg=13) => FUEL INJECTION SYSTEM (http://www.realoem.com/bmw/partgrp.do?model=HD63&mospid=47404&hg=13&fg=15)
http://www.realoem.com/bmw/diagrams/g/o/4.png
No. Description Supplement Qty From Up To Part Number Price Notes FOR VEHICLES WITH
WITHOUT CATALYTIC CONVERTER = NO
S199A=NO 01FUEL TANK BREATHER VALVEAB-ELEKTRONIK113901726705$71.7002BRACKET VENTILATION VALVE113901717292$3.2804FUEL HOSE6X11MM?1331127275005HOSE CLAMPL12-15207129952104$0.5606HOSE109/199013901735176$13.39
Notes: Items pictured but not listed are not installed on your vehicle.
Items pictured without a number are listed on another diagram.
Copyright © RealOEM.com (http://www.realoem.com/bmw/contact.do)

[genphreak]

OK, just removed the valve from the car and checked its operation on my benchtop power supply. It works like a champ, applying 12V closes the valve and without power applied it allows air into the engine, not out. Will check the connector on the car tommorow for power at the right time of course. So no leaky valve.

However the hose snapped under the manifold when I was removing it (old and brittle) so now I have to find a way to remove the hard, shitty bit left around the manifold connection which is behind the oil filter cannister, the droopy section of the intake plenum and the under the intake pipes.... it's truly an ass of a place to get to. Looks like I'll be pulling the plugs to check for lean burnt look. I always think Frieda's under powered and using too much gas, so am suspecting leaks. I guess it is called the hunt for absolute perfection.... :( Sacre bleu!

[Rustam]

Good work Rustam. So if one suspects poor economy, poor power, go pull the purge valve and clean or replace? I've had this problem (suspected vacuum leak for a very long time)

I am sure I need to replace the Charcoal canister in my car, am tempted to buy a new valve and canister and be done with it. Have you done yours yet? How much was it and where is best to get it? Anyone else doing it? Here we go again, I have to buy (another item) from the US again... :p

- is the valve you opened up easily cleaned without destruction? (ie I'm awaiting your write up!)

EDIT; As you called it a purge valve Rustam I got confused. Somehow couldn't find any such sucker on realoem so ended up thinking this must somehow be the fuel tank purge valve (non-return valve) instead, which is in the tank. Doh! feeling a bit woozy as it is right there staring me in the face: This is the sucker we're on about: Item 1.


Thank you Nick. I am not reposting the pictures - we can save some space.

I was not able to get to my website to start with new things, as I was a bit busy with my AFM partially in light of Bill R's comment. My car will have inspection done on Monday, so I also had to make sure things were adjusted, particularly because I cleaned the valve.

Now since the valve is cleaned, I noticed - stable startup in colder weather (still cold nights in NYC), stable idle, better response at acclereration and I think a bit better MPG.

I have yet to take a few pictures of a video I shot of the valve for the website.

I want to answer your questions:

Nick - DO NOT buy new valve, as the valve is extremely easy to fix. At least give it a shot.

I have not gotten new canister. I will be ordering mine from a place called BAVAUTO.com. I've ordered things from them a number of times - I like the way they treat customers - they are willing to listen and be patient. I don't mean to hint that a place or two mentioned above in this thread are bad - I simply don't know how they and I am not able to comment about them.

The valve opened up realtively easy. I did not take pictures for the opening procedure. Because it is too simple. Here it is:

(maybe redundant - see right after the procedure)

1 - Use small screw driver to push its tip at the seam between two halves of the valve. The edge of one half is formed as a cap - its rim wraps the other half along the circumference.
2 - Push the screwdriver along the circumference gradually, creating a trench between the rim of one half and the body of the other half.
3 - Once all circumference is separated, insert the screw driver and pry gently all around.
4 - The charcoal simply falls out once the petal is moved...
5 - Clean with alcohol and q-tip as needed.
6 - Check.
7 - Reseal.

Check:

I took a power adapter for wall outlet capable of producing 12V. My particular one was good for 1A. By attaching the leads to the adapter to the valve connector I got the reaction - the petal gets attracted to the opening of the outlet that leads to the intake manifold. This was enough for me to know that he valve was in good shape. I attached a flexible rubber pipe to the same outlet, and sucked the air out - with the valve open and then energized - simple test made me know it was good...
_________

Now, this whole procedure may be in fact redundant. I opened the valve becasue I had no idea of its exact construction. BUT! I imagine that spraying carb cleaner in side (from the thinner nozzle - in the direction of air flow through) and simply blowing through may take care of the problem without the trouble of opening. I would wait for a while to let it dry inside before applying current.
_________

I am attaching a picture for clarification before opening:

[Rustam]

OK, just removed the valve from the car and checked its operation on my benchtop power supply. It works like a champ, applying 12V closes the valve and without power applied it allows air into the engine, not out. Will check the connector on the car tommorow for power at the right time of course. So no leaky valve.

However the hose snapped under the manifold when I was removing it (old and brittle) so now I have to find a way to remove the hard, shitty bit left around the manifold connection which is behind the oil filter cannister, the droopy section of the intake plenum and the under the intake pipes.... it's truly an ass of a place to get to. Looks like I'll be pulling the plugs to check for lean burnt look. I always think Frieda's under powered and using too much gas, so am suspecting leaks. I guess it is called the hunt for absolute perfection.... :( Sacre bleu!

And I typed and typed...

Anyway, it is good to know that the valve is fine. Yes, that place on the manifold is absolute hardship to get to... I replaced this hose long ago - when I first got the car. I was tempted to start doing things with it so I took the manifold off. Just beacause I wanted to. I replaced that hose with simple plastic hose with nylon lining, that I boutght at a hardware store and it works just fine (tough though - 1000psi rating). The original hose seems to be the type used for gas delivery - at least it is that tough to compress.

My point is, having my hose there for a while perform up to expectations, I see no reason in getting exact BMW uinit.

[Alexlind123]

Thank you Rustam, i will clean my valve soon. I have had a rough idle for awhile now, worse in cold weather.

[Rustam]

Thank you Rustam, i will clean my valve soon. I have had a rough idle for awhile now, worse in cold weather.

Alex you are very welcome.
Every one is very welcome, I am delighted to be able to contribute...

[jbourke]

By carefully tapping a small screwdriver around the rim I managed to separate the two valve halves quite easily. Clean as a baby's bottom inside and it is the original. With 215 K's I doubt this valve will be causing much trouble.

My 2 cents,

John

[genphreak]

By carefully tapping a small screwdriver around the rim I managed to separate the two valve halves quite easily. Clean as a baby's bottom inside and it is the original. With 215 K's I doubt this valve will be causing much trouble. My 2 cents, JohnThanks John, mine was fine too, looks newer than the car and is clean and dandy inside. You can look down the pipe when inspecting if you have the right light behind you. Tested w 12V and it seals just fine too. I suspect if they get bits of carbon in there it might be the fault of the carbon filter (from the factory even) it wouldn't take much to upset that little sealing mechanism. :) Nick

[Mordan]

Interesting thread. Digging it out because I would like to fully understand the charcoal purge valve.

So can someone do a summary by filling the blanks :)?

Normal State =

DME Activated State =

When does the DME active it ?

Symptoms of stuck Open =

Symptoms of stuck Closed =

Thanks a lot.

[genphreak]

Interesting thread. Digging it out because I would like to fully understand the charcoal purge valve.

Normal State = Closed

DME Activated State = Open

When does the DME active it ? During startup- may be throttle related to prevent pushing fuel mixture down the line during 0-occasioanlly positive pressure situations (gearing down, engine braking, perhaps)

Symptoms of stuck Open = Always draws fuel vapour into the manifold, destruction of the charcoal effectiveness (needs repalcement each year anyhow) and yet another soucrce of unmetered air going into the manifold. (Slight fuel economy impact)

Symptoms of stuck Closed = Doesn't draw fumes from the fuel tank, so tank will pressurise regulalry instead of very occasionally depending on the weather/use pattern.



Good questions! :)

[ss2115]

I just replaced my charcoal canister after reading this thread.
Ever since I aquired the car, its always smelt of petrol after a fillup and for the first couple of days and then disappears.
We've been over the tank plastic tank for leaks and also the air breathers etc in the wheel arch with no stains or signs of leaks. Checked the fuel sender gasket as well - no leaks.

So I'm hoping this is the cure.

by the way - seems to me that if charcoal pellets are a problem being suchked out of the canister and into the purge valve, inserting a cheap inline fuel filter between canister and purge valve would prevent this. In my M50 it would sit under the power steering resevour and not even be seen.

[Mordan]

great answers! thx genphreak

let us know if it solved your gas smells!