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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > O2 Sensors...



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      06-06-2007, 07:20 PM   #1
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O2 Sensors...

I have no cats. I have a PROcede.

My AFR is running lean because the post-cat O2 sensors are reading ineffiecency (It is the post-cat o2 sensors that adjust AFR correct?).

I need a better understanding of how the sensor works (And if it isnt the post-cat I obviosuly just need to change the pre-cat sensor).

With the understanding of how the sensor works, would it be practical to add resistors to the circuit to trick the ECU/DME, or would I need to set up a variable operated system (Piggyback)?

Terry for once this is acutally a good time to get some input from you, if you know anything about the technical side of this circuit I would love to know.

Thanks
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      06-06-2007, 08:51 PM   #2
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Am I correct in thinking that with your theory, your car would be running lean even without the PROcede?... just because you dont have cats? Have you verified your AFR?
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      06-06-2007, 09:56 PM   #3
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Quote:
Originally Posted by schneid4323 View Post
I have no cats. I have a PROcede.

My AFR is running lean because the post-cat O2 sensors are reading ineffiecency (It is the post-cat o2 sensors that adjust AFR correct?).

I need a better understanding of how the sensor works (And if it isnt the post-cat I obviosuly just need to change the pre-cat sensor).

With the understanding of how the sensor works, would it be practical to add resistors to the circuit to trick the ECU/DME, or would I need to set up a variable operated system (Piggyback)?

Terry for once this is acutally a good time to get some input from you, if you know anything about the technical side of this circuit I would love to know.

Thanks
With no cats you increase volumetric efficency so the engine runs a bit leaner. The precat O2 sensors monitor the A/F ratio. The Post Cat O2 sensors monitor the efficency of the catalytic converter and in some cases might trim out the fuel and ignition... at least thats what I was taught at BMW school.

So if you remove the cats the DME will try to adjust by increasing injector on-time. If the injector on time has reached it's limit then a fault will be set followed by a service engine soon light.

How do you if you're running lean?
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      06-06-2007, 09:59 PM   #4
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Quote:
Originally Posted by RiXst3r View Post
Am I correct in thinking that with your theory, your car would be running lean even without the PROcede?... just because you dont have cats? Have you verified your AFR?
Yeah dyno'd it the other day. Getting a copy of the dyno is a bitch though.

Yes you are correct, reason I stated I have a procede is im not sure if there is an I/O on the PROcede to the O2 sensor, or an open I/O
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      06-06-2007, 10:04 PM   #5
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Quote:
Originally Posted by jon@themshop View Post
With no cats you increase volumetric efficency so the engine runs a bit leaner. The precat O2 sensors monitor the A/F ratio. The Post Cat O2 sensors monitor the efficency of the catalytic converter and in some cases might trim out the fuel and ignition... at least thats what I was taught at BMW school.

So if you remove the cats the DME will try to adjust by increasing injector on-time. If the injector on time has reached it's limit then a fault will be set followed by a service engine soon light.

How do you if you're running lean?
Dont get your question but I think i answered it in my previous post. So how would I go about tricking the DME, any way with resistors? Im pretty sure the Post Cat is triming the fuel, can the Pre Cat change the A/F or just monitor?
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      06-06-2007, 10:08 PM   #6
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Quote:
Originally Posted by schneid4323 View Post
Dont get your question but I think i answered it in my previous post. So how would I go about tricking the DME, any way with resistors? Im pretty sure the Post Cat is triming the fuel, can the Pre Cat change the A/F or just monitor?
Well what I meant to say is what is your A/F ratio?

Since you don't have a cat aren't you getting a service engine soon light?

Now the post cat may trim the fuel but in very very small amounts or none at all. The precat o2 sensor is a big input in controlling fuel injector on time so it does monitor A/F and can also control fuel injection.
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      06-06-2007, 10:19 PM   #7
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Quote:
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Well what I meant to say is what is your A/F ratio?

Since you don't have a cat aren't you getting a service engine soon light?

Now the post cat may trim the fuel but in very very small amounts or none at all. The precat o2 sensor is a big input in controlling fuel injector on time so it does monitor A/F and can also control fuel injection.
Not exactly sure what it is right now, but it is lean (My ever so trusted Performance guy has informed me, I wasnt at the Dyno). Yes, I am getting the CEL but only recently (Possibly a blown Pre-cat sensor, it used to come on and off when i hit the govenor but now i threw like 6 generic codes)
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      06-06-2007, 10:56 PM   #8
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If the 335 is like other cars the pre-cat sensors determine af ratio, post cat sensors make sure the cats are working efficently. If you have an af ratio issue, it's likely a pre-cat sensor issue. Also possible your af is fine and your guy is wrong.

On the post-cat sensor, it's not so easy on a 335. You can try the off the shelf simulators, and if those don't work perhaps a voltage reducing circuit (2 resistors) to show ~1v might do it.
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      06-06-2007, 11:29 PM   #9
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If the 335 is like other cars the pre-cat sensors determine af ratio, post cat sensors make sure the cats are working efficently. If you have an af ratio issue, it's likely a pre-cat sensor issue. Also possible your af is fine and your guy is wrong.

On the post-cat sensor, it's not so easy on a 335. You can try the off the shelf simulators, and if those don't work perhaps a voltage reducing circuit (2 resistors) to show ~1v might do it.
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      06-06-2007, 11:56 PM   #10
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Quote:
Originally Posted by schneid4323 View Post
Not exactly sure what it is right now, but it is lean (My ever so trusted Performance guy has informed me, I wasnt at the Dyno). Yes, I am getting the CEL but only recently (Possibly a blown Pre-cat sensor, it used to come on and off when i hit the govenor but now i threw like 6 generic codes)
Do you have a piggy back and do you know if the dyno operator is aware that a direct fuel injection system normally runs a bit leaner than a manifold injection system?
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      06-06-2007, 11:57 PM   #11
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Quote:
Originally Posted by jon@themshop View Post
Do you have a piggy back and do you know if the dyno operator is aware that a direct fuel injection system normally runs a bit leaner than a manifold injection system?
Yes I have a procede, no
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      06-07-2007, 01:34 AM   #12
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who made the downpipes for you? and also can you give us an idea of what you made with power gains.

no one with a 335 has Downpipes with no cats on this forum except you.

any info you can give us on, how it feels, who made them, what it cost you, power...etc would be great

thanks.

also if you can let us know exactly what your AFR was on the dyno.
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