What is the normal state of the Evaporative Purge Valve?

[the cheat]

Is it normally closed or normally open? I have been trying to track down (another!) vacuum leak and I have a pulsing vacuum on the hose coming out of the EPV into the charcoal canister. Is the valve supposed to allow vacuum all the time?

How difficult is it to open the valve to clean it? I have read a writeup on opening it and it essentially says to just pry it apart - is that correct?

Any input? I have the testing method from the service manual which states it should hold vacuum from the manifold side when 12v is applied but under what criteria does the 12v get applied? I can't find this component in the ETM.

[shogun]

If the valve is working properly, it is sprung closed and powered open.

1. Fuel vapour is created in the fuel tank when the engine is not running. The EVAP system stores this fuel vapour in a charcoal canister.
– when engine is cruising: purge control valve opened, small amount of fuel vapour is drawn into the intake manifold and burned.
– when the engine is idling (starting cold): purge valve prevents any vapours from entering the intake manifold and causing excessively-rich fuel mixture.
2. A faulty EVAP system will only affect engine driveability when the engine is warm.
http://diychamber.com/2010/03/how-bm...-system-works/

http://www.ricksfreeautorepairadvice...it-malfunction
Read more: http://www.justanswer.com/questions/...#ixzz0mjQdecKT


Canister Purge Valve Part Description
The Canister Purge Valve is a computer controlled solenoid valve that allows any stored fuel vapors in the Charcoal Canister to be recycled back in to the engine combustion process. This valve is controlled by the Power Train Control Module or PCM. The Canister Purge Valve is closed each time the Power Train Computer runs the OBD-II ( Onboard Diagnostic Generation II ) EVAP Monitoring self-test. This valve is typically located on or near the Throttle Body.

System Overview

The Evaporative Control (EVAP) System captures any raw fuel evaporating from the fuel storage system (e.g. the fuel tank, the filler neck, and fuel cap). Under precise operating conditions dictated by engine temperature, speed, and load, the EVAP system stores and purges these captured fuel vapors back into the combustion process.

How Part Functions In The System
The Evaporative Control System is designed to not only capture, store and purge any raw fuel vapors that leak from any areas of the Fuel Storage System but also to run a series of self-tests that confirm or deny the Operational and Vapor Holding ability of the System.

The Canister Purge Valve performs 2 important functions. It meters the flow and amount of stored Fuel Vapor that gets recycled or 'purged' back in to the combustion process from the Charcoal Canister. It also plays a role in the 'leak-test' by allowing a vacuum to be created in the entire Fuel Storage and Evaporative Systems when the Canister Shut Off Valve has closed and is preventing any outside air from entering either system. This is an important task because at least 20% of the Vehicle produced Air Pollution originates from malfunctioning Vehicle Fuel Storage Systems.

There are many ways for vehicles to 'leak test' the Evaporative System, but most perform the leak test either when the vehicle is sitting, say over night, or shortly after initial start up after the vehicle has been sitting over night. The Evaporative Systems operational performance is also tracked by the Power Train Computer by reading the change in the Oxygen Sensor voltages and Short Term Fuel Trim when ever the stored Vapors are released or 'purged' back into the combustion process. These values should indicate that fuel is being added to the system and that the over all mixture is getting richer. The purging process occurs when the vehicle is under acceleration, which is when most vehicles require additional fuel.
http://repairpal.com/canister-purge-valve
http://www.bimmerwerkz.com/forum/3-s...lem-68637.html

Diagnostic Trouble Code (DTC) P0444

EVAP Purge Control Circuit No Signal





Features of the Circuit


The evaporative emission (EVAP) system comprises the following components:

Fuel tank.
EVAP vent solenoid.
Fuel pipes and hoses.
Fuel vapor lines.
Fuel cap.
EVAP canister.
Purge lines.
EVAP canister purge valve.
EVAP service port.

Further Details:

The evaporative emission system is probed by applying vacuum to the EVAP system and monitoring for a vacuum decay.
The engine control module (ECM) monitors the vacuum level through the fuel tank pressure sensor signal.
The EVAP canister purge valve and the EVAP vent solenoid are turned on at the nick of time, allowing the engine to suck up a small vacuum on the entire EVAP system.
After the requisite vacuum level has been obtained, the EVAP canister purge valve is switched OFF, locking the system entirely.
If sufficient vacuum level cannot be derived, a large leak is indicated. This can be caused by the following conditions :
Missing or faulty fuel cap.
Disconnected or flawed fuel tank pressure sensor.
Disconnected, damaged, pinched, or blocked EVAP purge line.
Disconnected or erroneous EVAP canister purge valve.
Disconnected or faulty EVAP vent solenoid.
Open ignition feed circuit to the EVAP vent or purge solenoid.
Damaged EVAP canister.
Leaking fuel sensor assembly O-ring.
Leaking fuel tank or fuel filler beck.
Any of the above conditions can set DTC P0444.

The test is aborted if the tank vacuum is < 10 in H20 for 15 seconds and the manifold vacuum integral is > 49512 (proportional to purge mass from the tank).

and more http://www.bba-reman.com/content.asp...NEXT_DTC_P0444

[the cheat]

I felt around under my charcoal canister housing and didn't feel a bottom, just what felt like foam.

Should I be able to create and maintain a vacuum if I block one of the ports on the canister? In other words, is it completely sealed? I have a feeling that my can may have a hole in it and isn't allowing the system to keep a vacuum.

Update: I removed the EPV, applied 12v to it and attempted to put a vacuum on both sides. Both sides leaked very quickly. The service manual suggests it should be 20 seconds so I think I found my leak - or at least another leak.

[shogun]

from my charcoal cannister there goes from it's cap a plastic pipe to the front of the car under the lower washwater container, that is the drain. When you remove the lower wash water container behind the headlights, you see the pipe.

[the cheat]

I have repaired my EPV and am going to post a writeup on it.

My canister seems to have nothing underneath it.



Guess it should

[shogun]

pipe number 24

[the cheat]

I don't have anything under the canister itself... but I did fix my valve!

[shogun]

then the pipe broke off the cap, have seen some lose pipes when the plastic of the cap broke, anyway, that is not too important, it is for moisture drain.

[whiteghost1]

I don't have anything under the canister itself... but I did fix my valve!

Did you just take it apart and clean it? I used to have a 'pulsating' vacuum from the EPV at idle that was quite significant, I took it apart and cleaned it and the pulsating is still there albeit miniscule, but it is still there.

Has your pulsating disappeared completely when you fixed your valve?

[shogun]

here is a sketch of all the vacuum hoses on the 735
http://www.nmia.com/~dgnrg/hose_map.jpg

[the cheat]

Did you just take it apart and clean it? I used to have a 'pulsating' vacuum from the EPV at idle that was quite significant, I took it apart and cleaned it and the pulsating is still there albeit miniscule, but it is still there.

Has your pulsating disappeared completely when you fixed your valve?

I haven't been out to the car to reinstall it yet but according to the service manual my valve failed the diagnostic by not holding a vacuum. After fixing it (look here) it now holds vacuum. I did have a significant pulsing vacuum from it before - I believe the valve should be normally closed to hold vacuum durin engine operation and opens to pull in the fumes from the canister. If the valve won't hold vacuum, there is a leak in the manifold and should affect engine performance.

I haven't had a chance till just now to reinstall the valve. Let me just say that I think I finally have no more vacuum leaks! I had the WORST hesitation when I first pushed on the pedal and an almost diesel-like idle. Car hasn't idled this good since I've owned it!

So aside from the exhaust smelling like it's running rich, it seems to be running pretty damn good. I'm sure I have something else to repair - probably related to the o2 sensor.

I had NO hesitation at all during my normal ride in. The engine used to lose power when I would get on the gas from idle because of the vacuum leak. Now it's smooth until I sharply let off the gas, which I think is something not vacuum related and more of a fuel delivery issue.

[whiteghost1]

"You will have two halves - one side has a little plastic thing that holds a spring against a rubber stopper. Not sure what this is supposed to do - maybe prevents backflow."

I think I might have lost a small piece of the puzzle (rubber stopper) as I don't remember that being in there during reassembly, hence after cleaning I am having a small pulsating instead of the large pulsating felt before - when it was probably stuck open.

[the cheat]

I don't think the rubber piece really does much, other than keep errant fumes out of the valve when the engine is off. You might not have used enough RTV and still have a leak somewhere.

Does it hold vacuum? There really isn't an easy way to verify this but if you can get a squeeze bulb and attach it on the large end it should hold vacuum.

[whiteghost1]

I don't think the rubber piece really does much, other than keep errant fumes out of the valve when the engine is off. You might not have used enough RTV and still have a leak somewhere.

Does it hold vacuum? There really isn't an easy way to verify this but if you can get a squeeze bulb and attach it on the large end it should hold vacuum.

I can check if it holds vacuum, it should when the engine is off correct? How's about during running or at idle, should it hold vacuum as well?

I will plug the vacuum line from the EPV->intake manifold and see if my idle/driveability changes, that way I'll know if it is the source of my intermittent rough idle + engine roughness at ~2500rpm.

[the cheat]

if you energize the two posts on the valve with 12 volts that will close the valve and it should hold vacuum. Otherwise the valve is open.

The valve should be closed when the engine is idling, you can confirm this with a test light.

[fcubaiii]

hey i was just going through this post n saw a picture of the charcoal canister. i rebuilt my bmw 318i n im trying to figure out where the front tube (#24) gets connected to.

[shogun]

you should ask on the E36 forum. In case you mean the same tube like on the E32, on my 750 there is one which just ends in nowhere under the chassis to drain moisture/water.

[shogun]

quick test of fuel tank breather valve:The fuel tank breather valve should have a resistance of 45 ohms ± 20 and be closed in de-energized state.

https://web.archive.org/web/20130724...DME11-735i.pdf see page 13
in stromlosen Zustand ist das TE-Ventil durch ein Rueckschlagventil bis zu einem Saugrohrunterdruck von 20 mbar geschlossen

that means even without 12V the TE valve is closed by a back pressure/check valve up to a suction pipe vacuum of 20 mbar, = over 20 mbar it will open

[shogun]

Just found some good pics here from the webpage of a member here from an E31 850, copied text and pics:

The charcoal canister on these cars are notorious for rusting due to being located under the washer tank (which often leaks). The purpose of this canister is to absorb any fumes from the gas tank when the engine is not running. When the engine is running these fumes are fed into the intake manifold and burned off. It is a very simple device that is simply packed with activated charcoal and some gauze filters. They cost about $130 to replace but can be rebuilt for a lot less and so that is what I did...
http://www.km5tz.com/images/850i/char1.jpg
The washer bottle (located above the charcoal canister) was cleaned with hand cleaner. I replaced the grommets that seal the washer pumps and level sender and also replaced one of the pumps which appeared to be leaking.
http://www.km5tz.com/images/850i/washerbottle.jpg
The charcoal canister was sanded and primed with rust reformer. http://www.km5tz.com/images/850i/char5.jpg
I then drilled out the 4 dimples that retain the end cap. http://www.km5tz.com/images/850i/char4.jpg http://www.km5tz.com/images/850i/char10.JPG
This is the end cap and filter that hold the charcoal granules in place. http://www.km5tz.com/images/850i/char12.JPG http://www.km5tz.com/images/850i/char13.JPG
Looking down inside the canister with the charcoal removed you can see a removable gauze filter..http://www.km5tz.com/images/850i/char14.JPG
This is the activated carbon I used. It is a bit coarser then the original stuff but should be fine. It is primarily used to clean aquarium water and this cost me only $14 on Ebay (shipped). http://www.km5tz.com/images/850i/char20.JPG
I refilled the canister, re installed the white filter and end cap (now held in place with 4 x 4-40 SS hardware), then cut out and installed a new outer filter as the original disintegrated when I removed it. http://www.km5tz.com/images/850i/char21.JPG
Here's the finished rebuilt and painted charcoal canister with new hoses ready to be re-installed in the car http://www.km5tz.com/images/850i/char22.JPG

[shogun]

Symptom - Cold Engine - start Ok - idles at 750 for 1 sec then hunts 8 to 11

found this info posted on the E34 Bimmerboard forum by BMW-Test-Pilot, who owns an E34 535 with the M30 engine, same applies to the E32 735:

Symptom - Cold Engine - start Ok - idles at 750 for 1 sec then hunts 8 to 11 Author: BMW-Test-Pilot Posted on: 2016-12-07

Symptom - Cold Engine - start Ok - idles at 750 for 1 sec then hunts 8 to 11 times between 750 and 1000, then idles at 750 rpm - runs great, instant pickup when given a squirt, drives as it should.

Warm to hot engine - start - idles 750rpm.

It was the EPV - or Evap Purge Valve stuck open.

12v at terminal to EVAP PV, could blow gentle air both ways through.

Apply 12v to EVAP PV - no click - no close - still open air both ways

Started with Carb cleaner, then brake cleaner then WD40 small amounts of compressed air - LOTSA BLACK expelled from both sides. Sprayed WD40 into both tubes - left over night - repeated several times until clear WD40 was expelled. let dry.

Apply 12v and CLICK - no air either way. Re-install and no more idle hunt.

'89 535

[shogun]

MAINTAINING YOUR FUEL VAPOR RECOVERY SYSTEM
Government-mandated emissions standards were put in place in the early ‘70s. Since then, automobiles (including our BMWs and MINIs) have been subject to ever more stringent requirements regarding substances that are released to the atmosphere. While exhaust emissions have gotten the majority of the attention, there are indeed other emissions which have also come under scrutiny and control. The most important of these is the evaporative fumes from the raw (or unburned) gasoline.

Almost all vehicles on the road today have a raw fuel, vapor recovery system. The fuel tank on your BMW or MINI needs to vent as the fuel is drawn out and used in the engine. If there were no provision for venting, a vacuum would develop in the tank and soon the fuel pump would not be able to draw the fuel out and deliver it to the engine. In the old days (before the government mandates), car manufacturers handled this with a simple vent tube from the tank to the outside air. Unfortunately, this allowed raw fuel vapors to go directly into the atmosphere. To prevent this, car fuel systems now employ a closed venting system that, in the end, burns the collected fuel vapors in the engine.

As with the various other systems on our BMWs and MINIs, the vapor recovery system requires maintenance. All passenger vehicles 1996 and later have rather elaborate systems which include such things as pressure and leak sensors and valves that are monitored by the On Board Diagnostic (OBD) system. The basic system, found on almost all BMWs and MINIs, consists of the fuel filler cap (gas cap), fuel and vapor separation tank, charcoal canister, purge valve and the associated rubber tubing connecting the system together. Later models include pressure sensors and self testing systems that can detect leakage in the vapor recovery system.

In the vapor recovery system, the gas cap seals the fuel system, the charcoal canister receives and stores the raw fuel vapors, and the purge valve (in the line between the canister and the intake manifold) controls the flow of vapors from the canister to the engine for burning.

A faulty gas cap – one that does not close properly, has a missing or damaged seal, etc. – will allow vapors to escape to the atmosphere and will compromise the vapor recovery system. But it can also cause a fuel smell, poor emissions and fuel economy, and possible damage to the fuel pump and pressure regulator.

Over time, the charcoal canister will become saturated by the fuel vapors and will no longer be able to contain the vapors and fumes. If you have raw fuel smells but can detect no fuel leaks, you may indeed have a saturated charcoal canister. The canister can also become clogged, or plugged, by over-filling the fuel tank. If you (or the prior owner) had been in the habit of filling the fuel right up to the top of the filler neck instead of stopping when the nozzle first clicks off, raw fuel can enter the vapor recovery system and saturate the charcoal. If this happens, the canister must be replaced. A saturated canister not only causes noxious fuel smells and poor fuel economy but, left for a longer period, can cause damage to the fuel pump and fuel pressure regulator.

Charcoal canister on mid '80s BMW, located in the engine compartment.
Charcoal canister on late '90s BMW (96-99 3-series E36), located under spare tire in trunk.

The purge valve: Also known as the Fuel Tank Vent Valve or Breather Valve, this valve controls the venting of the stored vapors (in the canister) to the engine (via the intake manifold). Upon command from the Engine Control Unit (ECU), the valve opens and the vapors are drawn into the engine to be burned along with the standard fuel and air mixture. A faulty purge valve that stays open all the time can effectively cause a vacuum leak. If it remains closed all the time, it can cause pressure in the venting system and/or the same symptoms as a saturated charcoal canister.

When to replace these items:
• Replace your gas cap if it does not snug down tight to the filler neck or if the seal is dry and hard, cracked, or missing.
• Replace the purge valve if it is not functioning properly (see the appropriate manual for diagnostic procedures) or if an engine fault code points to it.
• Replace the charcoal canister if your BMW or MINI is older than 10 years, has more than 150,000 miles – or if you suspect the fuel tank was ever over-filled. Also, if you smell gas but cannot find any leaks, the canister is a good bet.
• Finally, inspect the vacuum and vent hoses for looseness or cracks, which will cause vacuum leaks.

article from http://blog.bavauto.com/11767/bmw-an...rs-diy-how-to/