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      04-06-2019, 07:07 PM   #1
ericbikes
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Identify part and loud air leak

Hi- I have E39 and I get loud hissing left side of engine coming from bottom hose of this silver part that looks like some kind of vacuum part. Can someone pls identify? The loud leak sound seem like it's coming from wherever the hose goes down to that under the car I can't see what it's connecting to.

The loud leak sounding noise stops after about 60 seconds of starting cold engine and does not happen starting warm engine. Never happened before.
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      05-19-2019, 05:02 PM   #2
hans_e39_530i
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The valve in question is called Secondary Air Injection Valve. The BMW part number is 11727540468
This is the EGR valve. It is pneumatically actuated and so, when starting, it should make some hissing sounds if it is still emptying the air in the accumulator. After the vaccum pressure is achieved, it should really stop.
If i recall correctly, the EGR opens in the high load area of the engine map, so that the temperature in the combustion chamber is reduced, say, from 750C to 400C. This happens because the EGR lets exhaust gases in the combustion chamber and so, reduces oxygen concentration. The reduced temperature reduces the formation of poisonous NO2 (the Nitrogen from the air ends up oxidized in high temperature).
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