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Discussion Starter #1
So i'm troubleshooting my secondary air system related to codes pulled for a service engine soon light. I've checked the hoses and they are good. I disconnected the secondary air pump hose that connects to the check valve and did a cold start. A surprisingly large amount of air is coming out of the pump.

The next morning, I disconnected the small tube on the check valve and did a cold start and found no air exiting the fitting on the check valve. Does this mean that the check valve is bad? If so, can it be cleaned instead of just replacing it?

For reference I'm talking about item #1 in the following diagram.

http://www.realoem.com/bmw/showparts.do?model=DT43&mospid=47584&btnr=11_2203&hg=11&fg=45
 

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I disconnected the small tube on the check valve and did a cold start and found no air exiting the fitting on the check valve.
That is a vacuum line. Air will be sucked into pipe / vac line #4

That fitting allows air to be pulled on a diaphragm in the diverter valve (check valve) allowing air being pumped from SAS pump to enter the exhaust manifolds. This is done (SAS pump runs for 30-60 seconds) to burn clean through the cats until they get up to temp after cold start Better for the environment and all that...

If you are getting codes and the SAS pump is pushing air, replace the plastic POS hose from the pump to the diverter valve, the rubber vacuum line to the diverter valve and the diverter valve gasket and copper nuts.
 

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Discussion Starter #3
That is a vacuum line. Air will be sucked into pipe / vac line #4

That fitting allows air to be pulled on a diaphragm in the diverter valve (check valve) allowing air being pumped from SAS pump to enter the exhaust manifolds. This is done (SAS pump runs for 30-60 seconds) to burn clean through the cats until they get up to temp after cold start Better for the environment and all that...

If you are getting codes and the SAS pump is pushing air, replace the plastic POS hose from the pump to the diverter valve, the rubber vacuum line to the diverter valve and the diverter valve gasket and copper nuts.
To be clear the diverter valve is item 1 in the link I provided, correct?

And, if I remove the diverter valve should air be exiting where it is mounted?

If it's supposed to and doesn't, we can be sure the valve is frozen in the closed position and definitely bad, no?
 

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#1 is the diverter valve.

Don't remove it unless you are replacing it.

The large port on the left side of the valve in the parts diagram is where the hose from the SAS pump terminates.

The small port with the line to it from #4 is where the vacuum line terminates.

IF you remove the large hose from the SAS Pump and there is air coming out of it at cold startup ... your pump is fine.

IF you remove the small hose and there is suction on (in) it at cold startup, your vacuum lines is fine.

If you have never changed this part, and you are getting codes, and the plastic hose to the SAS Pump is FULLY intact, replace the diverter valve. The plastic hose from the SAS pump to the diverter valve fails OFTEN and is typically full of holes that the previous owner covered with black electrical tape. If your codes are for low air input ... most often it is the large hose that has failed. The SAS pump moves quite a bit of air .. even f the large hose from it has holes you'll still feel air coming from it at cold startup (SAS pump operation).

I recommend replacing it proactively as well b/c the valve, gasket, copper nuts and plastic hose are a LOT cheaper than the SAS pump.

Cheers.
 

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This is how the system works during COLD start. All of these parts are activated simultaneously during COLD start:

1. Electrical signal from computer ---> Check Valve #5, now it is open to allow vacuum from Intake Manifold to suck on the Air Valve #1.

2. The Air PUMP (Passenger's side wheel well) now pumps large amount of air into the medium-sized hose toward the Air Valve, waiting for the Air Valve to be opened by the Check Valve. Once the vacuum reaches the Air Valve, it opens.
Now the air can be pumped into the Exhaust system (Large Red Arrow).

- If you have alot of air coming from the Air Pump, it is good news, b/c the Air Pump is still good. The Air Pump is expensive ($250-350 range). BTW, I wrote a DIY for Air Pump replacement if you need it later.

http://www.bimmerfest.com/forums/showthread.php?t=459397&highlight=sas+air+valve

- With the medium-sized hose disconnected (as above) but vacuum hose still attached, run the engine and with a mirror, look into the Air Valve port, you should see the flap moving up to allow air from Air Pump. With your palm, you should feel some vacuum sucking on the Air Valve Opening. If this flap does not move it is either:
a. Bad Air Valve
b. Something wrong with the vacuum circuit (see below).

- If you have no vacuum (air sucking on the finger when you apply the finger on the vacuum hose) then it is either:
a. bad vacuum hose (cracked hose)
b. defective Check Valve #5.
This is why the pro, when dealing with a potential bad Air Valve #1, replace all 3: Air Valve #1, vacuum hoses, and the Check Valve #5 to simplify later diagnosis. Actually this is the procedure recommended in the BMW TIS.


 

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+1 on what everyone else says. A diverter valve failure is usually the primary culprit for SAP system failures. When that valve fails, hot exhaust air can enter the pump, where it condenses and then kills the pump. A very good idea is to proactively change your valve to avoid a pump failure ($300+). A very common failure mode is the cracking of the rubber vacuum hose (#4) that connect the plastic pipe (#3) to the valves. This leads to insufficient vacuum to activate the diverter valve. Every time I do a Vanos job, we tear that rubber vacuum hose as it gets very brittle sitting above the exhaust manifold. If you removed it from the diverter valve, I would bet it is cracked now, if it wasn't before.
 

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Discussion Starter #7
I neglected to mention that I replaced the short section of hose that goes from the diverter valve (item #1) to the long tube that runs parallel to the engine (item #3).

I'm having a hard time accessing the rear of the engine to fully examine the vacuum hose where it connects to the check valve (item #5). I took off the engine cover but it's really tight back there. Any hints? I borrowed an inspection mirror for the next time I find time to attempt it.

BTW codes were P0491 and P0492.
 

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If you remove the passenger side microfilter housing and air tube to the firewall it should give you more room to inspect.

Still, is sort of a blind operation.

Be careful in that area as the plastic firewall piece right behind the cylinder head becomes brittle with heat/age and will fall to pieces if you push on it. I've had to replace mine after barely touching it during the valve cover gasket/ dual vanos seals replacement.
 

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Discussion Starter #9
If you remove the passenger side microfilter housing and air tube to the firewall it should give you more room to inspect.

Still, is sort of a blind operation.

Be careful in that area as the plastic firewall piece right behind the cylinder head becomes brittle with heat/age and will fall to pieces if you push on it. I've had to replace mine after barely touching it during the valve cover gasket/ dual vanos seals replacement.
Thanks will try removing the housing. Doesn't help that I have XXL hands and sausage fingers. :)
 
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