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Discussion Starter #1
Hey guys and gals.
I would appreciate some input here. I am experiencing a strange situation with my E46 N42B20 (4cyl).
I failed the MOT bc co values are high.

I pulled out my scan tool to read the values. Cyl 1 and 4 are bank 1.
B1s1: - 0,20 mA indicating rich condition
B2s1: - 0,04 indicating slightly rich condition.
But the short term fuel trims on idle are:
B1: 5%
B2: - 5,5%

Downstream narrow band sensor gives me 0,68 v which confirms the rich exhausts.

So the b1s1 sensor is telling the ecu that the exhausts are rich, but the stft indicates that the ecu is ADDING MORE fuel. What in the world is going on here?


Appreciate any ideas.
 

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Discussion Starter #3
Thanks for the reply.
STFT
B1 5%
B2 - 5,5%
LTFT
B1 0,0 %
B2 - 3,9 %

Dont have maf values right now can post them later if you need it for analysis. The only trouble code is an intermittent catalyst conversion rate on pre-cat bank 1. I dont think that should impact fuel trims bc its just a check on the catalyst no?

The thing that jumps out at me is that the ecu is adding fuel but the sensor is reporting rich on bank 1.
The maf affects both banks thats why I did not suspect it first.

Thanks
 

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Discussion Starter #5
Great idea. I had the manifold off ths weekend to change the downstream sensor (stuck is an understatement) and I was not 100 sure which wire went where. I put them back what seemed most reasonable bc of the length of the wires but did not double check with the scanner.

I appreciate your help BaliDawg. Will post back in a couple of weeks when I had the chance to test it.
 

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Discussion Starter #6
Found the time now to check it. Unfortunately everything looked ok. They only fit one way, wires are not long enough to mix them up.
The maf hot idle value is 2,25 g / forgot the value but second?
The rest of the values are very similar to what I posted before.
I had the intake off a few weeks ago when I changed the ccv if that helps. And The engine keeps a steady 105 degrees C which it should.
 

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Hey guys and gals.
I would appreciate some input here. I am experiencing a strange situation with my E46 N42B20 (4cyl).
I failed the MOT bc co values are high.

I pulled out my scan tool to read the values. Cyl 1 and 4 are bank 1.
B1s1: - 0,20 mA indicating rich condition
B2s1: - 0,04 indicating slightly rich condition.
But the short term fuel trims on idle are:
B1: 5%
B2: - 5,5%

Downstream narrow band sensor gives me 0,68 v which confirms the rich exhausts.

So the b1s1 sensor is telling the ecu that the exhausts are rich, but the stft indicates that the ecu is ADDING MORE fuel. What in the world is going on here?


Appreciate any ideas.


Are you sure that's true. I have not looked it up, but balancing the load on the crank would dictate to me that the firing order would be 1-3-4-2. The DISA splits the intake into Bank 1 and Bank 2, but B1 and B2 are driven by the exhaust manifold, not the intake. On the Inline 6, 1 and 4 are different banks of exhaust, the only diagram I have of the I4 are a different engine family than you have, and the engine you have is not offered in the USA market.k If you have a split exhaust manifold, then you surely have B1 and B2, but if the manifold is a single unit then you should only have B1.
 

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Discussion Starter #8
The car is a euro-4 version with 2 pre-cats on the exhaust manifold. Cyl 1 and 4 go into one cat and 2-3 go into the other.
Cyl 1-4 has a sensor 1 and a diagnostic sensor 2 post cat. Cyl 2-3 only has a pre-cat sensor.

I am pretty sure. Only Europe had these euro-4 models. US got the Euro-3 without pre-cats if Im not mistaken.
 

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Thanks for the reply.
STFT
B1 5%
B2 - 5,5%
LTFT
B1 0,0 %
B2 - 3,9 %

Dont have maf values right now can post them later if you need it for analysis. The only trouble code is an intermittent catalyst conversion rate on pre-cat bank 1. I dont think that should impact fuel trims bc its just a check on the catalyst no?

The thing that jumps out at me is that the ecu is adding fuel but the sensor is reporting rich on bank 1.
The maf affects both banks thats why I did not suspect it first.

Thanks
No, the Pre-CAT B1S1 is reading the exhaust immediately after leaving the combustion chamber. This is the sensor where rich and lean are measured. The Post-CAT sensor (B1S2) is the check on the CAT. P0171/P0172 is fuel trim (lean or rich, respectively) on B1, P0420 is CAT efficiency, B1.

QUESTION
Is the fuel trim reporting that the mixture is rich, or is it reporting that it is trying to add fuel because there is too much air? Didn't you say that you replaced the intake manifold gasket, or something? This would tend to indicate you have a vacuum leak that is sending the fuel trims high to add gas to correct the lean condition.
 

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The car is a euro-4 version with 2 pre-cats on the exhaust manifold. Cyl 1 and 4 go into one cat and 2-3 go into the other.
Cyl 1-4 has a sensor 1 and a diagnostic sensor 2 post cat. Cyl 2-3 only has a pre-cat sensor.

I am pretty sure. Only Europe had these euro-4 models. US got the Euro-3 without pre-cats if Im not mistaken.

I would agree that only the EU, and maybe other markets that are not North America, got your engine.

You say at the beginning of the sentence that 1&4 have sensor 1, and only 2&3 have a pre-CAT sensor. Sensor 1 and Pre-CAT sensor are the same thing. One of us is confused. I see here that you have 2 sensors, both are B1, one is S1 the other is S2.
 

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Discussion Starter #11 (Edited)
Jdstrickland Thanks for your reply. I reread my posts and I fail to see what I have got wrong. I am confused? Please be more mindful of your language. I said there is one manifold with two integrated cats on it and three sensors.
Cyl one and four go to the same cat. For that cat there is a sensor one and two. The pre cat sensor is a wide band and The second a narrow band.
Cyl two and three go into the same cat. That cat only has a upstream wide band sensor but not after.
As far as I can tell this is what I tried to say from the start.
Btw the link that you sent does not even picture the euro4 model so it doesnt help.
 

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Discussion Starter #12
No, the Pre-CAT B1S1 is reading the exhaust immediately after leaving the combustion chamber. This is the sensor where rich and lean are measured. The Post-CAT sensor (B1S2) is the check on the CAT. P0171/P0172 is fuel trim (lean or rich, respectively) on B1, P0420 is CAT efficiency, B1.

QUESTION
Is the fuel trim reporting that the mixture is rich, or is it reporting that it is trying to add fuel because there is too much air? Didn't you say that you replaced the intake manifold gasket, or something? This would tend to indicate you have a vacuum leak that is sending the fuel trims high to add gas to correct the lean condition.
Aha I see where you got me wrong now. Ok. You see the euro4 model has THREE cats. Two are on the manifold and The third is further down. I wrote pre-cat and meant first cat, you thought I meant the pre-cat sensor.

My bad I could have been clearer
 

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Thanks for your reply. I reread my posts and I fail to see what I have got wrong. I am confused? Please be more mindful of your language. I said there is one manifold with two integrated cats on it and three sensors.
Cyl one and four go to the same cat. For that cat there is a sensor one and two. The pre cat sensor is a wide band and The second a narrow band.
Cyl two and three go into the same cat. That cat only has a upstream wide band sensor but not after.
As far as I can tell this is what I tried to say from the start.
Btw the link that you sent does not even picture the euro4 model so it doesnt help.

What I am reading has a conflict in my head. Did you look at the link I gave you to realoem.com? I just made some guesses as to what you have, and posted the result. At the top of the page there are links, one of them is Select Another Car. Choose that one and plug in your VIN and the result should be exactly your car. Copy and paste the page and I can see what you are working with.

According to the diagram I gave you (based on the guesses I made), you have 2 sensors, one on each side of the CAT. If I have the wrong diagram of your engine/exhaust, then that would explain why I am confused by what you are telling us (me). It's entirely possible to have a split manifold with a sensor on each branch that goes into a single CAT, which is what you seem to be describing, but I have never seen such a configuration so I am confused.
 

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Discussion Starter #16
Like I said those two on the manifold are just the first cats. There is a Main one downstream. The manifold has three sensors. Two for bank one and one for bank 2. You can see on the pic it is divided into cyl 1-4 and 2-3.
 

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Holy confusion, Batman, there are sensors at Items 1, 2, 3, 12, & 13. 1 and 2 are giving B1 and B2, respectively. I'm not sure what 3 is telling you. 12 is telling you that the CAT efficiency is okay (it's Sensor 2), and 13 is telling you that the secondary CAT is okay, I think OBD II refers to it as Sensor 3 but I don't know. I have heard about this configuration, but have not seen it.
 

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Discussion Starter #20
Holy confusion, Batman, there are sensors at Items 1, 2, 3, 12, & 13. 1 and 2 are giving B1 and B2, respectively. I'm not sure what 3 is telling you. 12 is telling you that the CAT efficiency is okay (it's Sensor 2), and 13 is telling you that the secondary CAT is okay, I think OBD II refers to it as Sensor 3 but I don't know. I have heard about this configuration, but have not seen it.
I noticed sensor 12. There is no 12 on my car. Never has been. I dont know why it is in the schematic. There is only a narrow band after the Main catalyst. It is referred to as b1s3 by the ecu.
Yes the configuration is a complete clusterf*ck and has given me a lot of headache. But the Main problem as I said seems to be in bank 1. The wideband sensor there gives me - 0,20 mA and so is detecting a rich condition.
I checked the fuel rail/injectors and they are not leaking. I pulled the rail out and turned on the ignition to pressurize them.
I am leaning toward a bad WB sensor.
Any ideas are appreciated.
 
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