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We I checked the pressure on the cats and the pressure was good. Was told they weren't clogged. Now I am wondering if the downstream O2 sensors are bad and that's causing the problems. I didn't realize the down stream O2 sensors were connected so far away from the cats. Order two new sensors today so I will try that out and see what happens. May need to replace the upstream O2 sensors as well. Thoughts???
Did you use a name brand gauge to test? I used a junk Chinese brand and my back pressure tested ok as well. The only time I saw abnormal back pressure readings was when I'd be at 2k rpm and then rev is fast to 4k or so. I still believe your cats are the issue. The code you are getting is the classic code. The BMW specific code is 28a2. Can you pull the BMW specific code using something like pa soft?

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Also, a bad post cat 02 sensor wouldn't throw the air path code you're seeing. It also wouldn't throw the car into limp mode.

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What was the pressure and RPM readings? Like everyone is saying, it***8217;s usually fine at low RPM but bad at higher RPMs. It doesn***8217;t take much either. There is a recent thread on bimmerfest where 3.5 PSI back pressure on just 1 bank was causing the problems.
 

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Hi Everyone,

I am new to this forum, however, I hear its awesome. Anyways, my wife's 325i starting to go into limp mode after reaching 45 mph or 4k rpms. The EML light, traction control light and brake light would come on and the car would go into limp mode. As soon as she pulled over and turned the car off and then back on, the problem would go away. I hooked up my Foxwell scanner to the car and received a P16A7 error code.

Here is what I've done to attempt to fix the problem. I changed the crankshaft sensor, both cam sensors (intake and exhaust), cleaned the throttle body and examined the disa valve. I also changed out the intake boots. Proud of myself, I took my wife for a ride after I put the car back together and 10 minutes later - BAM - it went back into limp mode.
montanakidd:
As several others have previously mentioned, most likely your cats are restricted. Here is the back pressure tester that I bought to find out that my cats were severely restricted:
https://www.amazon.com/dp/B01EMKFGZ2?tag=e46fanaticsconvert-20

Any measurement over 0 psi at idle or over ~1.25 psi at 2500 rpm means the cats are restricted. At these small pressures, a reliable tester is mandatory. Here is a link to a thread where another forum member went through the same sort of gyrations as you and ended up having to replace his cats:
https://forum.e46fanatics.com/showthread.php?t=1249699
After I replaced my cats, I tried cutting one of them open. The surface of the honeycomb did not show any clogs. Only when I held the honeycomb up to the sunlight, could I see that the passageways were somewhat obstructed. All this says to me is that using a scope to look at the cats through the pre-cat O2 Sensor holes is not a reliable test.
Hope you find the culprit.
 

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Discussion Starter #27
Hi Everyone,

Just wanted to let you know I've removed my cats and will be ordering new cats tomorrow. Does anyone have any suggestions on where to order them from? Reasonable price? I will let you know when they arrive and I get them changed out. Thanks guys.
 

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Montanakidd,
I'm going through the same issue you are currently and ready to pull my hair out because I can't definitively diagnose the issue. I tried an old-fashioned intake manifold vacuum test which in theory is a reliable test for exhaust backpressure (what goes in must equal what comes out) and it came back fine, but everyone on here is saying to do an actual exhaust pressure test, so I may do that.

Did the catalytic converters fix your issue? Did you end up going with OE or aftermarket cats?
 
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