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Old 02-05-2012, 06:45 AM   #41
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Join Date: Jul 2011
Location: Charlotte NC
Posts: 2,747
My Ride: 2001 BMW 330ci
Originally Posted by Kirk330i View Post
So does anyone know the real operation of the vacuum circuit for the SAP system? I'm trying figure out why I'm have no resistance in the line from the vacuum actuated valve at the SAP and the electric solenoid valve under the intake runners. Let me see if I get this straight, and anyone with the knowledge please correct me, here's how I see it working;
- On a cold startup, the SAP turns on to flood the exhaust manifold with air (oxygen) helping to reduce emissions and help heat the CAT.
- Simultaneously, the DME sends an "open" signal to the solenoid valve under the intake runners. When this opens, it vacuum actuates the vacuum valve by the SAP to open, allowing air into the manifold.
- After approx. 90-120 sec., the SAP turns off (via DME command), and I'm assuming, the DME closes the intake solenoid valve thereby shutting off vacuum to the valve at the exhaust manifold and air into the manifold.
- Car warms up, all systems go.
Simple, right? So I'm trying to figure my best odds here before I start throwing $$ at it. If it's just a vacuum line gone bad, no problem (yeah right, if you're Houdini and can reach under there!). If the solenoid valve is shot, then I would like to buy it before ripping into the teardown (still haven't figured out the best way to get at the valve) and they aren't cheap! Sorry to all if I'm rambling, I just think that if I find out what's up with my shudder issue then it might help someone else with lean running issues. Thanks again for the thread!
You pretty much have the sequence of events right. I had to replace my solenoid, because the plastic hose had degraded, and pieces of it had been sucked into the valve. I was not comfortable using it, even after cleaning it out, so I replaced it. It is a ***** to get at. I would try reconnecting a new hose first, and see if it is strong enough to activate the valve at the SAP. It is a pain to work on, because the car has to be cold when you test it, so it takes a while. If the hose has been open, then it may have been sucking trash into it, especially if the plastic hose has been breaking down, and pieces of it have landed in the valve. But try replacing the hose first. It helps to have someone with small arms, to reach around to connect it to the valve. Removing the entire cabin filter housing helps too. Clean out the valve at the SAP too, so you can be sure it is not sticking closed. I used carb cleaner to do that. If you do not get enough vacuum to open that valve, then you will have to replace the vacuum solenoid. But unless you had an issue like mine, where pieces of the vac line were being sucked into the solenoid, it should be OK. The solid section of that vac line, the plastic tube, is pretty expensive too, so I replaced the entire line with Teflon vac line, covered with braided stainless steel to withstand the heat. I think I already mentioned that somewhere in this thread. I found it on eBay. They sell it here:,940.html
And here:,4294950883
But Speedway also has an eBay store. This is where I got mine:
You will have to cut off the ends they have on the pieces they sell.
Now, I have not driven my car more than a few hundred miles with this stuff, so I can not say for sure it will stand the test of time. But it does have a high heat resistance, and I liked the idea of replacing that multi-piece assembly with a single line. There were too many places for the factory piece to fail. If yours is like mine, then you have a rubber line, connected with the plastic section (which I am guessing was used because of the heat in that section of the line), and then another connection to the second rubber line that ran to the SAP valve. The connectors at both ends of the plastic pipe were broken on mine, and the pipe had become so brittle that it was cracking and pieces of the plastic had broken off, and I found some lodged in the solenoid. So, the stainless shielded Teflon line was an experiment on my part, and if it held up, I was going to create a post about it. But it seems to be coming up more and more on the forums, so I guess it is starting to fail quite often on the older cars. I think this may be the source of vacuum leaks that people can't seem to find, even after replacing their other lines and intake pipes. But that is just speculation on my part. I had been getting codes for a long time, even though my other vac lines were fine. I only found this because my SAP started sounding a lot louder, because the valve was not opening. I thought the SAP itself was going bad. I know the PO of my car had replaced his SAP just before I bought it, because he gave me the old part. After I found this, I hooked up the old one, and it was fine, so I suspect this issue was occurring when he owned the car, and the BMW techs just replaced the SAP and called it a day. Sorry for the long post, but like you, I am rambling on a bit too. tL/dnr: replace the line first, before buying a new solenoid.
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