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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Fri, Apr-08-2016, 06:18:42 PM   #51
Jrrrrrrr
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Default Re: Vapor Trails: code FD, evap valve stuck closed

Pictures are fixed.

Quote:
Originally Posted by mkm3 View Post
So I would recommend others having this problem to purge the emission lines and driving the car for a bit before replacing parts.
It seems to do the trick again and again for me. I've had to do this several times over the last few years and each time a little bit of compressed air keeps the CEL away from months-a year. I would bet the issue is the charcoal canister media disintegrating and flowing off into the fuel evaporative plumbing. Replacing the canister might be the ultimate fix, but isn't cheap of course. On the other hand, throwing parts at the problem doesn't always work. My car passes smog easily and never ever throws and other emissions monitor-related codes besides the one that is the subject of this thread.

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Originally Posted by Nipps View Post
Noob question, but can anyone help me by explaining how to get the 12v to the canister and the shut off valve?

Thanks!
You only need to power the purge valve (not the canister or its shutoff valve) in order to allow airflow to pass through. Use a AC-DC 12v power supply and a female bosch fuel injector harness pigtail. You can get the pigtail from various volvos, VWs, Audis, Saabs, and other Euro makes from a junkyard. I use the PS from this HDD kit for auto electric troubleshooting, as just one example:

http://www.ebay.com/itm/IDE-SATA-to-...3D220764567409

Last edited by Jrrrrrrr; Fri, Apr-08-2016 at 06:24:11 PM.
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Old Sat, Sep-24-2016, 08:27:08 AM   #52
LivesNearCostco
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Default Re: Vapor Trails: code FD, evap valve stuck closed

Thanks to all who contributed to this thread. I've had the Peake 11-Fd code (P0446 on regular scanner) on and off for some months. It happens more often right after filling the gas tank and tends to go off after several drive cycles with the tank not full. I replaced the vent valve on the charcoal canister and that didn't help.

Then I blew some air through the vent tube (black tube attached to charcoal canister by vent valve) and into the blue line that leads from the purge valve to the charcoal canister, but without disconnecting that line from the canister. At that time I didn't understand the hose routing so I thought the black hose by the vent valve was the one going to the purge valve up front (silly me). After that, the CEL light seemed to come on less often but the P0446 code was still often pending even when the light was off.

After more research I understood the system works like this. For the actual E36 OBD setup, just add a vapor-to-liquid tank above the fuel tank with a pressure sensor and a second line from the liquid-vapor tank to the charcoal cannister.


There are only 2 relevant valves--vent valve and purge valve--and 2 relevant sensors --fuel tank pressure sensor and O2 sensors. The O2 sensors check if the mixture gets richer when the purge valve is energized, but they cannot really be used to test the vent valve. The vent valve is normally open to the atmosphere and the purge valve normally closed. When the car is stopped and heating up or you're filling the tank, vapors from the gas tank flow through the liquid-vapor separator then into the charcoal canister (via one blue line) and out the black vent tube. When you're at higher speeds the DME opens the purge valve to suck fresh air into the vent tube, through the charcoal canister and into the intake manifold.

The normal way to detect a stuck-closed vent valve is to apply vacuum by opening the purge valve and closing the vent valve with the engine running. Then close the purge valve, check the fuel tank pressure (vacuum) and open the vent valve to see if the vacuum disappears quickly enough. If vacuum doesn't disappear quickly enough, it reports vent valve stuck closed. If the system won't hold vacuum with both valves closed, it reports an EVAP leak. If energizing the purge valve during high speed driving doesn't lead to a richer mixture, it reports a problem with the purge valve. If your vent valve is actually stuck closed, you will have trouble filling the fuel tank (unless one of the other hoses is broken) and will often hear a whoosh when opening the fuel cap.

There is no way for the DME to directly pressurize the system. While it could theoretically close both valves and see if rising temperatures increase tank pressure, I am fairly sure the DME uses only the one method described above. So when this error comes up there can only be a few causes:
  • Vent valve stuck closed or failed, or wiring to vent valve shorted
  • Vent hose clogged
  • Blockage of line from charcoal canister to liquid-vapor separator
  • DME got old and is too demanding to the pressure-drop test
  • Pressure sensor failed
  • Purge valve broken or leak in one of the hoses (or fuel filler cap) prevents DME from setting vacuum for the test. But then I think it would set a leak code and not P0446.

With this understanding, I disconnected 2 blue lines and one large black hose from the charcoal canister, took it out, and blew air into both ports where the blue lines connected. Dumped some dust out of the canister vent opening. Blew air into the blue purge line from the front and verified air came out of the other end by the canister. Removed right rear wheelwell liner and verified the hoses all seemed intact. I forgot to blow air into the 2nd blue line (goes to liquid-vapor separator) with the gas cap open.

Then I found a big spider egg sack in the exit of the black vent tube. It was stuck in there pretty well, and as you know spider silk has a very high strength-to-weight ratio. Obviously it didn't completely block the vent tube or I would have trouble filling the tank, but maybe it was enough to prevent vacuum from being filled quickly enough during the test? I then went to fill the tank and drove around a little without any CEL. But it's too soon to tell if the problem is fixed.

Remaining question is why would the P0446 code come on more often right after filling the tank? My only guess is a full tank temporarily blocks liquid-vapor separator so when the vent valve is opened after a vacuum test, it doesn't increase pressure in the fuel tank quickly enough to satisfy the DME.

Last edited by LivesNearCostco; Sun, Sep-25-2016 at 01:40:43 AM.
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Old Tue, Oct-18-2016, 11:22:25 PM   #53
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Default Re: Vapor Trails: code FD, evap valve stuck closed

In the last 3 weeks I've filled up at least 2 times and situation is same as what Jrrrrr reports: Pending P0446 code most of the time but no CEL. I'll have to go through a few more fill-up and drive cycles to be sure this is fixed (or at least not so blatant to turn on the CEL).
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Old Tue, Jun-13-2017, 09:40:54 PM   #54
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Default Re: Vapor Trails: code FD, evap valve stuck closed

I like your theoretical info in the previous post and agree with most of it. The exception is that my car would throw the CEL for FD/P0446 at seemingly random times - recently filling up had nothing to do with it.

Also, four years later, and the CEL is still gone. It hasn't come back in well over a year and a half and I haven't even had to do my compressed air-purge procedure. At some point a pending FD code did come back which I can only see with the Peake tool. There is no standard pending P-code. I haven't cleared codes or lost battery power in a long, long time, though, so I have no clue when that pending Peake code may have showed up.
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Old Wed, Jun-14-2017, 06:30:41 AM   #55
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Default Re: Vapor Trails: code FD, evap valve stuck closed

Hey that's great to hear. I haven't had the P0446 code since last October, so I guess clearing out the black vent tube fixed it for me.
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Discussing Vapor Trails: code FD, evap valve stuck closed in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)