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Charcoal Canister Removal
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TOPIC: Charcoal Canister Removal

Re: Charcoal Canister Removal 2 years, 7 months ago #63768

  • PDS
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I had a perplexing problem where my car would gradually lose power during a session and when I would pull into the pits I could hear the fuel pump screaming.

I disassembled the fuel pump - replaced the fuel pump and inspected the tank very carefully. The tank was clean as was the pump filter.

When I was at Summit last year the problem continued. Fortunately Paul Poore was there and suggested that I cut the vent line from the canister. Viola - the problem was gone!

Later that weekend I had the misfortune of coming in contact with a GTS Porsche (I'm being very kind to him here!) and went off outside of turn 6 and struck the embankment. After a breif period of beautiful blue sky I ended up on me head.

Fortunately, there was no fuel leak from the vent hose. The car was upside down for at least 10 mins and no evidence of fuel leakage anywhere. I had approximately 2/3 full tank.

Based on my experience I believe that the later models - mines a 89 - use the charcoal cannsiter as the sole vent for the tank. Or at least mine was buggered up enough that it would not vent at all.

I'll be taking the suggestion of placing an inexpensive fuel filter on the end of the line.

Re: Charcoal Canister Removal 2 years, 7 months ago #63772

  • Ranger
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PDS wrote:
I
Based on my experience I believe that the later models - mines a 89 - use the charcoal cannsiter as the sole vent for the tank. Or at least mine was buggered up enough that it would not vent at all.

In order to better understand our DME I've had some conversations with tuners that hack them and burn chips. Apparently the DME opens the line to the vent cannister briefly once each trip. IIRC correctly it was during or shortly after start-up.

My point is that it might be a mistake to think of this as a vent if the solenoid is normally closed. And if it's not normally a vent, I'm not sure we want to put a filter on it and turn it into one.

Later edit. PDS, that was a great story. You should go into more detail and post videos.
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Last Edit: 2 years, 7 months ago by Ranger.

Re: Charcoal Canister Removal 2 years, 7 months ago #63774

  • Foglght
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So, we need to look at a fuel system diagram here. This should tell us all we need to know.
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Re: Charcoal Canister Removal 2 years, 7 months ago #63776

  • PDS
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Ranger, wish I could post a video - Murphy's Law..... The time that you forget to turn on your video something spectatcular will happen....

Funny note - the morning of the crash my son purchased a helmet hook at the track vendor for a fathers day gift to me. I mounted it on the front halo tube. When the car came back on the wrecker the hemet hook was proudly sticking through the roof sheet metal. Had puched a hole right through and the hook was not bent or scratched in any way.

Re: Charcoal Canister Removal 2 years, 7 months ago #63777

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You need some form of venting, being canister of through the cap, but imagine the level of vacuum you would be pulling on the tank if it has no way of venting on a long drive!
If it was me I would fit a anti roll valve in lieu of the canister and a filter.
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Re: Charcoal Canister Removal 2 years, 7 months ago #63795

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OK, some confusion now. Last night I removed the cannister. Per my previous post, I had solved a fueling problem by cutting the vent line to the cannister. Tank was previously building neg pressure and i was losing fuel pressure.

After removing the cannsiter I checked to see if the remaining vent line on it was plugged. It was not. Air moved freely in & out of the cannister connections. Hmmmmmmm. If air moved freely how could the vent line be plugged?

I'm not sure how the internals of the cannister work however could it be possible that the electric valve under the manifold had failed and was always in the open position? Could this cause engine vacuume to create neg pressure at the tank?

Another point; the original fuel problem would be alleviated once the motor was turned off. I could start it right back up and the issue would not present itself until I went back out on track.

Is this one of lifes' great mysteries - I did so & so and the problem was fixed but I have no damed reason as to why.

Re: Charcoal Canister Removal 2 years, 7 months ago #63796

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PDS wrote:
OK, some confusion now. Last night I removed the cannister. Per my previous post, I had solved a fueling problem by cutting the vent line to the cannister. Tank was previously building neg pressure and i was losing fuel pressure.

After removing the cannsiter I checked to see if the remaining vent line on it was plugged. It was not. Air moved freely in & out of the cannister connections. Hmmmmmmm. If air moved freely how could the vent line be plugged?

I'm not sure how the internals of the cannister work however could it be possible that the electric valve under the manifold had failed and was always in the open position? Could this cause engine vacuume to create neg pressure at the tank?

Another point; the original fuel problem would be alleviated once the motor was turned off. I could start it right back up and the issue would not present itself until I went back out on track.

Is this one of lifes' great mysteries - I did so & so and the problem was fixed but I have no damed reason as to why.


Certainly if the purge valve was stuck open it would put a vacuum on the purge tank. I don't know how the purge tank is designed, but if it's entirely dumb then I supposed that would apply low pressure to the gas tank. Of course the gas tanks vent tube at right rear, if working, would prevent any low pressure zone from developing.

The purge valve being stuck up would be surprising. It's normally closed and doesn't open unless it gets 12V. Something that is held closed by a spring and opens only briefly should normally fail in the closed position I figure. But heck, anything can happen.

What if there was a short and the purge valve was getting 12V all the time? That would certainly do it.
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Re: Charcoal Canister Removal 2 years, 7 months ago #63811

  • AndrewK
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The canister purge valve is normally closed and opens only when told to by the DME. I always understood that occurs either during coast or cruise (i.e. part throttle opening, but not full throttle). Can't recall the details beyond that.

At other times, in order to prevent a vacuum, I believe the gas tank sucks air in through the holes at the bottom of the charcoal canister. That's the only place I know of where that action could occur. Everything else in the system is sealed up once the gas cap is on. This would also explain why people pull a vacuum when they plug that line shut.

For anyone that has not had a good look at all the myriad gas tank vent lines, the parts diagram on Real OEM will help explain the layout. You can derive the function from that as well. There is a small plastic vent line from the gas tank to the bottom of a plastic tank up above the right rear wheel. There is a larger vent line from the gas tank that connects to the top of the filler neck and the top of the plastic tank. Any vapors that condenses back to liquid in the plastic tank will drain back to the gas tank via the smaller hose at the bottom. Vapors that do not condense in the plastic tank are routed from the top of the plastic tank via the third line, to the charcoal canister, and finally into the intake. These three vent lines are what is hidden under the metal cover behind the right rear shock.

I plan to terminate my canister vent line the way it's done on euro E30s that didn't have a charcoal canister from the factory. They simply vent to the atmosphere through a rubber end on the small plastic line from the top of the plastic tank. The rubber end drops down next to the gas tank near the fuel pump. Although I may use a small filter instead of the rubber end in order to keep spiders out of my tank. I know I've seen pictures of said rubber end, but too busy to search the web at the moment.

The rubber end piece is shown as #12 here:

realoem.com/bmw/showparts.do?model=1231&mospid=47263&btnr=16_0104&hg=16&fg=10

As for gas spilling out of the canister vent line in a roll over, I don't see how that could happen. Gas would have to get to the plastic tank in the fender and then work it's way down the canister vent line. When the car is upside down the canister line is the high point and liquids don't flow uphill. If the car is lying on the passenger side, although the plastic tank would fill with gas, the canister line is still at the high point. When lying on the driver side the plastic tank is the high point and gas won't even leave the main tank.
Andrew Kratzer
1988 325is (Spec E30)
1988 M3 (Retired from track duty)
1989 325i (S52 swapped daily)
Last Edit: 2 years, 7 months ago by AndrewK.

Re: Charcoal Canister Removal 2 years, 7 months ago #63812

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That was good info Andrew, thx.
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Re: Charcoal Canister Removal 2 years, 7 months ago #63846

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I finished this mod last night. I capped the charcoal cannister line at the fuel pump and fire wall then vented the line from the top of the expansion tank to atmosphere with a small fuel filter. Fuel shouldnt leak out in a rollover unless the expansion tank fills with fuel.
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