Bimmerfest - BMW Forums - View Single Post - Secondary Air System Issues
View Single Post
Old 02-09-2013, 08:59 AM
540iman's Avatar
540iman 540iman is offline
resident, old fart
Location: N.W. Indiana
Join Date: Sep 2008
Posts: 1,873
Mein Auto: 2002 540i sport
Hopefully, you have saved your old pump and valve. Likely the mechanic that changed your old pump tossed it, but maybe not. FYI, these pumps are re-buildable and easy to take apart and inspect for moisture in them. If they are dry, I usually just lubricate, clean the foam filter, and back on the car. The valve can be soaked in the stuff Autozone sells in a 1 gallon can sold as carb cleaner (have a gallon of it in garage, but forget who makes it). If you go to Autozone and ask for the 1 gallon can of carb cleaner with the built-in basket, they will know. Costs $25. Just soak valve overnight. This stuff has been proven to remove carbon build-up and I can attest that it really works! Will not damage your valves inner parts, but will remove any carbon that can keep the valve from closing fully which is the cause (usually) of the Piersburg pump failing from water rot or water freezes inside pump causing it to lock-up. Just some random info on the SAP system.
Pump is actually being used in an "over-speed" condition to push as much air as it does (as the O2 sensors need to see). If the pump were to run for longer than about 5 minutes, it will burn-up and be toast. This is also why the entire pump electrical is fused at 50 amps
thru fuse 107 which is a bitch to get at under passenger seat rug. 50 amps to salmon-colored relay in ECU box under pass. side cabin air filter. ECU sends 12v to relay for a "normal" ~90 second cycle on cold start-ups. Relay handling about 34 amp draw of motor often gets contacts "welded" closed causing motor to run "forever" which in reality is about 5 minutes and then it is shot and may take the 50 amp fuse with it if the motor encounters "rotor lock" before the windings gets so hot they short.

Water gets to the motor NOT from moisture in the exhaust going past a partially-stuck-open check valve, but because of the heat in the exhaust stream getting past a check valve that is not fully closed and the motor shuts off after the 90 seconds. Now, there is no air flow from the pump to "push the exhaust gases back" and the gases are now free to flow with no pump air flow to stop them back into pump which is cold and simply forms condensation inside the pump. Over time, this small amount of water becomes a small pool of water in the pump. Left outside overnight in a cold climate and now you have a frozen pump waiting for you to get in and start car. 90 seconds of current flow to a frozen pump causes pump failure, possible relay welding due to excess current draw or fuse 107 blowing.

When replacing pump, always replace valve as well or you are really taking chances.

Last common problem which happened to me on my personal car was like this. Replaced my frozen pump, relay, replaced fuse 107, valve, and hose from pump to valve. Entire system new and working properly, but still getting low air flow bank one and two errors. New pump out of the box had ever-so-slightly less power than old pump when it was working. Lines from valve to heads and heads had CBU (carbon build-up). There was enough carbon in the air path to no longer satisfy the O2 sensors which must see the exhaust stream go lean (enough) while pump is adding air ahead of convertors to exhaust stream. Two fixes-there are no "simulators" or "sims" to fool this system. $8000 repair where BMW gun drills your heads and replaces lines to get better air flow to exhaust. $300 fix (for me) which was purchase of Powerchips modified ECU which is generally bought for a supposed HP gain or performance gain, but they also can change your USA software to Euro software that does not need to see as much air flow at the O2 sensors to be satisfied. On a Euro car, if SAP system fails partially, they get no SES! Just sets a code that will only show during a scan. If you opt for the Euro software for SAP when purchasing a Powerchip, you will no longer see SES as long as all the components are installed properly and some amount of air is flowing. It basically opens up the parameters of air flow necessary to satisfy the O2s and ECU and our local emmissions people! Sorry to be so wordy, but in case there are others wanting to understand or are having similar issues.
Reply With Quote