Now how did you come the conclusion you needed to replace the bank 2 converter? Usually its the pre cat sensors that go before the post cat. And don't you have relatively low miles?

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Now how did you come the conclusion you needed to replace the bank 2 converter? Usually its the pre cat sensors that go before the post cat. And don't you have relatively low miles?

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The post-cat O2 sensor code was what got this investigation underway, but it is in no way related to the driveability issue. It was merely a "clue". If you think about it a lean code makes sense if the cat is clogged.

I also spent a few good hours researching the very rare P16A7 code. Almost all conclusions were clogged cats, and one scenario was a MAF. I pulled the MAF to test, car should've ran fine on the "default" engine management map, but it still went into limp mode.

 

If you look at fuel trims, look to see if your STFT is positive and LTFT is negative at idle, and then see if they trend negative with an increase in engine load.

Some quick tests of the cats (at operating temperature): using an infrared thermometer, measure in welds on the input and output sides of the cat; the output should be hotter than the front. If they're the same, or the rear is colder, you have a clog. Test both cats to compare.

If you have a vacuum gauge, attach it to the brake booster. at idle you should see 18-22 in-Hg. If you increase engine speed up around 3k RPM, vacuum should drop but then rise back quickly. If it stays low, you have confirmed an exhaust restriction. Next return to idle, but stab the throttle quickly to raise to 2500 RPM and let off; if the gauge drops to zero, restriction confirmed.

Loosen an upstream O2 sensor to see if the condition improves (despite the CEL for lean condition). If so, cat is faulty. If not, try the rear sensor; if the condition improves, the restriction is downstream of that sensor (muffler).

Same goes for your pressure tests: normal pressure should be 0, at most 3 psi, with the tester screwed in place of an O2 sensor. Run the engine up to 2500rpm; if pressure starts climbing north of 3 psi (especially getting close to 8), you have a clog downstream of the pressure tester. Check at both upstream and downstream sensors to isolate the variable.

Were all the O2 sensors in the car when mechanic was hammering about, and were all replaced? They don't handle any vibrations well (been there with an air chisel, got the T-shirt), they're less resilient than the Cats.

 

Hey Duke, good to see you.

I've never looked up STFT or LTFT, but I believe they're reported in INPA right? My E83 module comes up all German, despite the E46 module working in English.
An infrared thermometer is something I didn't think of, but I do have one. At this point I'm almost afraid to let it run but at idle there shouldn't be too much pressure to worry about.

I watched a couple videos on YouTube (EricTheCarGuy) for the vacuum gauge test so that's another option. Hopefully the exhaust back pressure tester arriving today will confirm the issue.
The SAP pump is out and the pre-cat O2 sensors came out easily as well. Took about 10-15 minutes to remove them.

In regards to your question about the sensors being out, the post-cat O2 on Bank 2 was removed when he did the hammering. Pre-cat O2 was still in its place.
With the car being higher up in mileage, I'm dreading the idea of removing the manifold. The nuts and studs next to the engine block look like crap..

Wonder if I have much of a case to take it back to my mechanic and have him replace the manifold with a new one I purchase, labour on his dime.

 

I’ve never used INPA but I’d have to assume you can see due trim values. Many generic scanners can access that info if you have one.

Tap the cats with a rubber mallet and see if you hear anything rattling around, as another test; you should be able to hear anything.

If all the above tests point to cats, the ILLEGAL option (have to say that) is to gut the cats, install defoulers and call it good. Removing the manifolds can be a total nightmare, especially considering the tight space for tools or heat. What I’ve had to do in the past when studs snap in an Al head is to just say hell with it, snap them, place a nut over the broken stud and fill the hole in the head with weld to extract the buried stud. But that requires the welder. For a lot of guys, it’s less work in the long run to yank the motor so you have easy access to everything. The fasteners could come out easy, or not, with the engine in place. Sometimes it’s also easier to just cut the cats off and weld new ones on rather than deal with removing the manifolds.

Another option is to disconnect the down pipe where it meets the exhaust pipe (2 studs which may have been replaced with bolts), and get a boroscope up the pipe so you can physically see the cats.

If you were to pull out the inner fender, would that provide access to get in there? If so, it may not be terrible.

I certainly would exhaust all tests before dealing with rusted, aged manifolds. I have to pull both manifolds and fill exhaust off my VW in the coming weeks, and I’m not looking forward to it.


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Just wanted to provide an update for anyone running into this issue in the future.
From all my internet research, yes P16A7 does 9/10 times point to the catalytic converters being clogged up, but not always.

Fortunately for me and for my pocket, I'm the 1/10 example.
I conducted the Exhaust Back-pressure Test and had good results. 0 psi at idle, and almost 0.5-1 psi at 4,000 RPM (gauge says to conduct at 2,500 RPM but I wanted to be sure).
I also drove around without the pre-cat O2 sensors (thereby bypassing any clog), and the car still went into limp mode, so that told me it wasn't the catalytic converters.

If you're doing the back-pressure test yourself, it should be done without any load to the engine (i.e. in Park or Neutral). I don't recommend driving without O2 sensors as you can start a fire.
Out of curiosity, I hooked up the gauge and went for a drive, trying a couple of WOT pulls as well - The gauge will start to climb in those circumstances, as mine did up to 6 psi.
If you think about it, that makes sense... this is what enables a turbocharger to work, so obviously your exhaust would create some pressure especially when you're accelerating with load.

Now.. onto the remedy:
It was the MAF (Mass Air Flow) sensor after all. I was extremely lucky to find a 2005 BMW 325i in the scrapyard which had just arrive & wasn't picked, so I took its OEM MAF.
If you have an MS45.1 vehicle with the 5-pin MAF, you'll know these are hard to come by. Don't ever buy a Chinese knock-off. Even a junkyard OEM one is more likely to work properly.


So that solves this problem. Car has full power again and no limp mode.
As luck would have it though, my trifecta of ABS, 4x4, and Brake lights came on the next day (intermittent), which so far I believe is pure coincidence.
BMW Scanner 1.4 is reporting it is a right rear wheel speed sensor, so a new Bosch one is in the mail. New transfer case fluid on the way as well.

Fingers Crossed!

 

Update 2: Right rear wheel speed sensor was grinded down by the axle.

New sensor installed and I used one of the transfer case crush washers to space it out a bit. No lights on dashboard, trifecta gone.

 

Did you clean and check the reluctor wheel? Sounds as if it is rusty and may be damaged. If so, look on eBay for replacement rings, from the UK last I saw.

Without a properly functioning ring, that sensor will send poor info to the computers. And you don't want the sensor raised so high, to clear hazards, that it misses creating impulses. Engine, auto trans, TC, and brakes will all be confused.

 

Yep, the rear passenger reluctor wheel is not a perfect circle - There must be some rust underneath it pushing it up on one side.
I cleaned all the surface rust and paint chips off of it, and also cleaned the rear driver side as PM. (added the 2nd TC crush washer on that side, lol)

Can these rings be replaced without removing the axle?
Almost seems like at my mileage if I need to change them, I might as well change the rear axles, no?

My speed sensor had it's metal contact exposed, so it was a gonner. As a side note.. the wheel speed sensor design on this vehicle seems very dumb.
I feel like a pebble or any sort of road debris can get between the reluctor ring and ruin it and the sensor at the same time.. am I the only one thinking this?