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Thread: Fuel Vapor Purge Charcoal Canister System Questions

  1. #1
    Join Date
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    E34 540i 6sp 1995-03-28

    Fuel Vapor Purge Charcoal Canister System Questions

    I have been hunting down a recurring O2/Lambda fault CEL bad running issue.

    When I bought this car last year one of the two lines IN to the canister was open not being connected to a hard line to the tank and so back at the fuel tank the other rubber segment is likewise free hanging open.

    I wondered if the CEL was happening when the purge valve opens and draws air in through the one open hose.

    Until I can fit a hard line between the two ends I pulled the hose off the Throttle Body Port, capped it and tightened a clamp over it... it seems to be running normal again but I left the hose just zip tied back over near the brake booster and so its just releasing whatever it draws from the tank right there.

    Maybe a naive question but is there any real risk of a spark igniting anything or is it never going to be concentrated enough?
    Last edited by jehu; 06-23-2019 at 12:59 PM.

  2. #2
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    11/88 E32 750iL+98 E36M3
    this is how it should be http://bmwfans.info/parts-catalog/E3...e/fuel_supply/
    the charcoal cannister actually has 3 connections, 2 for vapour in/out, and one open end hose for the moisture.
    Check the valve
    to test the valve: The tank breather valve should have a resistance of 45 ± 20 Ohm and is closed without volts/connector not attached. When it works, you can feel it clicking when touching by hand.
    From Test Instructions DME 1.1: Tank Vent Valve (TE = Tank Entlueftung Valve) Check: The TE valve is activated every second. The timing is palpable by hand.
    Check for tightness: Connect the vacuum supply from the service tester to the 8-mm connection (observe flow arrow). Adjust negative pressure to 600 mbar and supply TE valve with 12V. Switch off the vacuum pump, after 20 seconds the pressure drop must not exceed 50 mbar. When de-energized, the TE valve is closed by a check valve up to a suction pipe vacuum of 20 mbar.
    Test drive phases: The TE valve is activated in idle mode (display ON) and is thus closed. As soon as the lambda control is active and the speed is increased up to approx. 1600 rpm, the stepwise opening can be observed (display OFF).

    I disassembed such a valve and we tested it, see here on an M70 engine http://e32b12.blogspot.com/2012/09/m...ble-fix_5.html

    Maybe a naive question but is there any real risk of a spark igniting anything or is it never going to be concentrated enough?
    When I had the hoses brittle there and the breather valve basically bypassed due to cracked hose the engine idle was bad, as there was uncontrolled air/fuel mixture/vapor coming into the engine, also had a O2 fault code with the code reader.
    I don't assume that you risk spark ignition with that but the fuel/air mix is definitely not correct.
    Last edited by shogun; 06-23-2019 at 01:08 AM.
    Shogun tricks and tips for the E32 series are HERE!

  3. #3
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    E34 540i 6sp 1995-03-28
    Quote Originally Posted by shogun View Post
    this is how it should be http://bmwfans.info/parts-catalog/E3...e/fuel_supply/ but the fuel/air mix is definitely not correct.
    So this will be because the engine software has a value programmed for the volume of input from the purge system and whether I have cracked hoses which is possible and likely or I cap it off at the throttle I will still get faults?

    I'll try replacing the hoses and see how that works. I did get some idle changes when using propane gas around that area but considered it was the throttle gasket..

    Thanks for clearing up that the open hose is correct for moisture. I saw the impression of a clamp around the end in the wheel well and assumed it had been on a hard line.

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