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Old 01-18-2013, 04:01 PM   #6
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Join Date: Oct 2003
Location: Scenic Hudson Valley, NY
Posts: 115
My Ride: 328Ci, 328iC, X3
Originally Posted by glhx View Post
My SAP may have been bad for a long time and I not know it because i dont know what its supposed to sound like. I know ive never heard any distinct noises from that area while under the hood ever.

The SAP sends fresh air to warm up the cats....also sends fresh air to help burn the rich fuel when cold starting. This is where i could think they are related.

Did running rich for a long period of time on cold starts carbon foul the o2 sensor.....which is past its replacement date anyway. only speculating here.

my thoughts on this are that one or both of my precat o2 sensors are bad and went bad over time due to lack of SAP and wear and tear.

It could be the MAF....i found an app to measure MAF in g/sec. havent done this yet.
The SAP doesn't "warm up" the cats (can't warm something with cold fresh air), it just pumps additional air into the exhaust to help burn off uncombusted fuel until the cats get hot enough to do so on their own. I suppose it's possible that you have a bad O2 sensor, but for both to come up with faults at the same time makes me suspect that it's something else upstream that's causing both sensors to throw fuel mixture codes.

Also, if your SAP had not been working it should have lit up the SES light.
Got Miles?

2000 328Ci Steptronic
Original Engine & Transmission
Original Transmission Fluid
15K Oil Changes
So there!

Last edited by enzo_the_baker; 01-18-2013 at 04:03 PM.
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