Running lean.

[Morphine]

So I had a catless downpipe installed last week and was getting a CEL for running lean error from the bank 1 #2 sensor (post cat). It was installed with the U-Spacer and the middle size restrictor, then I completely removed the spacer altogether…still got the code.

I then attached the O2 directly to the pipe, and I am still getting the error, so I put the JB1 on map 0 and no CEL. But when I do a VCDS scan I still get a running lean code, just no CEL (better I guess).

Bank 1, probe 2 (post cat, Part #06K906262AC fyi)

I have logged both sensors and they seem to be working ok.

I am very confused, how can I get a running lean code with no cat?

Car is a 2016 R, MT….Mods specific to this problem may be.
APR Intake + Carbon Pipe
CTS Intercooler
CTS catless down pipe
JB1

 

[Morphine]

Ok so I removed the post cat O2 sensor and stuffed it in a gas soaked rag.

Reading are about 2.15v with the rag and .88 without the rag.

Sensor 1 lambda spec vs actual looks ok.

Will yank the JB unit and see what happens driving tomorrow.

 

[SLOWR]

I have the same reading on my R, I got the CTS catless downpipe too and the reading on the VCDS shows lean too! You'll get rid of the CEL light with a proper ecu tune.

 

[Morphine]

I still have my Eurodyne flash tool from my gti, so I just need the credits.

As I understand it these cars run lean to begin with, but without a cat I should be getting a rich CEL.

I can’t see an exhaust leak being the problem, the two sensors are only a foot apart and the pipe is mounted well. There is a bit of back and forth play in my turbo inlet pipe after I really went to town on it putting the intake pipe once…I wonder if I broke something.

I don’t have any fuel trim logs from my gti, but I would assume that the tunes richen-up the mix a bit for all the heat…can anyone confirm this. Perhaps it will simply make my problem go away. I was planning on going stage 2 in the next while anyhow?

I cant shake the feeling that something else is going on here though.

If any experienced users can explain to my dumb ass what is happening that would be great. How can I be lean without a cat?

 

[Morphine]

Gonna slap in the AEM wideband gauge I have lying around and see what that tells me.

Damn replacement O2 costs about 200 bucks, I dont want to drop that without a good reason.

Why...why do I always get catless?

 

[Chris@Revo USA1]

A lean code for a rear o2 sensor does NOT in anyway mean the engine is running lean.

The rear o2 sensor is there to confirm that the cat is working properly and has nothing to do with your actual running condition in regards to lean or rich.

Your car has a factory wideband sensor already you don't need to add one.

 

[George Smooth]

The lambda probe faults only trigger the engine light after the third or fourth recorded event. There is a plethora of different codes you can get from catless which includes rich to lean, lean to reach etc.
The faults are triggered when the car runs in open loop so on cold start and light throttle. In general the lambda distance from the primary plays a role as well as how far the actual probe is from the exhaust gases.

In terms of full throttle driving and the car going lean you will get a fault on the primary sensor which sits in the turbo S1 B1. This will stop the car immediately in its tracks. There is very small allowance on this from the ECU and it is highly sensitive to target vs actual.

 

[Morphine]

A lean code for a rear o2 sensor does NOT in anyway mean the engine is running lean.

The rear o2 sensor is there to confirm that the cat is working properly and has nothing to do with your actual running condition in regards to lean or rich.

Yup yup.


Your car has a factory wideband sensor already you don't need to add one

But it makes me feel so cool...besides I put the gauge pack and all the wiring in a month ago, it is just running the boost readings at the moment. All I need to do is weld a bung to the pipe and plug it in.

 

[Morphine]

The lambda probe faults only trigger the engine light after the third or fourth recorded event. There is a plethora of different codes you can get from catless which includes rich to lean, lean to reach etc.
QUOTE]

I did not know that, thanks.

In terms of full throttle driving and the car going lean you will get a fault on the primary sensor which sits in the turbo S1 B1. This will stop the car immediately in its tracks. There is very small allowance on this from the ECU and it is highly sensitive to target vs actual.

I had a hunch this was the way it worked, as the 1st sensor is wideband. Great information, thanks.

 

[Morphine]

Well...the CEL comes on all the time, I will get used to it as I know nothing is wrong. So it kind of becomes useless for when something actually does go wrong it will not warn me, or I will not take it seriously.

The post cat O2 sensor must be damaged in some way, even though the readings look ok....that does not make much sense to me though.

There is no way it is not getting enough flow to produce correct readings in the pipe...it is way in there.

 

[flipflp]

Well...the CEL comes on all the time, I will get used to it as I know nothing is wrong. So it kind of becomes useless for when something actually does go wrong it will not warn me, or I will not take it seriously.

The post cat O2 sensor must be damaged in some way, even though the readings look ok....that does not make much sense to me though.

There is no way it is not getting enough flow to produce correct readings in the pipe...it is way in there.

If you're running an aftermarket downpipe, catless or not, without a tune that disables the rear o2 sensors you will throw a code. Typically it's a catalyst efficiency code, because that's what the rear o2s check.

Without a catalytic converter, that rear o2 is seeing emissions values way outside of what is acceptable, that's what throws the code.

As far as safety is concerned, your front o2 is the important one.

 

[Morphine]

If you're running an aftermarket downpipe, catless or not, without a tune that disables the rear o2 sensors you will throw a code. Typically it's a catalyst efficiency code, because that's what the rear o2s check.

Without a catalytic converter, that rear o2 is seeing emissions values way outside of what is acceptable, that's what throws the code.

As far as safety is concerned, your front o2 is the important one.

You are partly correct here...a tune will disable the running rich code, but not the lean code....I think.

But as George stated there are a plethora of codes that can get thrown without a cat...I just did not think lean was one of them, I guess I was wrong.

 

[flipflp]

You are partly correct here...a tune will disable the running rich code, but not the lean code....I think.

But as George stated there are a plethora of codes that can get thrown without a cat...I just did not think lean was one of them, I guess I was wrong.

So I'm partly correct, you think huh? Haha

A "stage 2" tune will out right disable the rear o2 in some way. Some tuners eliminate the catalyst monitor outright, others just turn off the sensor. Regardless of what code you're getting, a tune would eliminate it. Piggy backs don't mess with that stuff.

Sent from my Nexus 6P using Tapatalk

 

[Morphine]

So I'm partly correct, you think huh? Haha

A "stage 2" tune will out right disable the rear o2 in some way. Some tuners eliminate the catalyst monitor outright, others just turn off the sensor. Regardless of what code you're getting, a tune would eliminate it. Piggy backs don't mess with that stuff.

Sent from my Nexus 6P using Tapatalk

I don’t understand why anyone would disable a lean code, even on a secondary (post cat, O2) probe that has nothing to do with adjusting fuel trims (1st sender, wide band).

That does not make sense to me as lean conditions are very dangerous. That’s like taking a flammable sticker off a gas can because there is no gas in it.

I don’t really want to argue about this, as it is not going to help me with my problem.

Perhaps one of the major outfits may post some information.

 

[Morphine]

Will try a replacement gasket tomorrow.

On the bright side I can now remove the pipe from the turbo and yank the sensor in under 5 mins.