Turbo back unitronic on a CARB version GTI

[gtrude]

Hi all. I’ve been running the stage 2 unitronic setup for a while now, and was never able to figure out the correct O2 sensor setup and was living with the CEL. For reasons involving an overlooked bad PCV and a new rear main seal, I’m motivated to resolve the sensor issue.

I’ve done this job n other cars using the spacer trick with a single CAT setup, but the second CAT and extra sensor on this one has me stumped.

Does anyone have any experience in how to put this together without the CEL (turns out that’s pretty important here in CT if I actually want to drive it)

Thanks

 

[JOHNDERS2586]

Seems to be varying luck to get rid of the CEL with spacers. So assuming like most aftermarket DPs you have 1 cat now. The first 02 is on your turbo , you don't do anything with that one. second is pre cat an third is post cat. The best way I've seen it explained is you are trying to show/trick a decrease in 02 readings as it progressively makes it's way down an out through the 3 check points essentially.. Some guys have had to fool with different spacers and spacer insert on both pre and post cat. Others like myself just did 1 J style spacer with the middle insert post cat an haven't had a cell since.. For reference I'm 14 CBFA with a KO4 and a catted DP.

 

[BudgetPhoenix]

It seems to vary case by case tbh. These cars are very sensitive to it. You will literally just have to keep experimenting to find what works but it seems like a lot of people have luck with the j-spacers. As for what direction they are pointing or how many is what you will need to figure out.


Or just do what most people do in cali do and just swap your stock parts back on for when it comes times for smog lol.

 

[Saabingti]

Hi all. I’ve been running the stage 2 unitronic setup for a while now, and was never able to figure out the correct O2 sensor setup and was living with the CEL. For reasons involving an overlooked bad PCV and a new rear main seal, I’m motivated to resolve the sensor issue.

I’ve done this job n other cars using the spacer trick with a single CAT setup, but the second CAT and extra sensor on this one has me stumped.

Does anyone have any experience in how to put this together without the CEL (turns out that’s pretty important here in CT if I actually want to drive it)

Thanks

What CEL do you have?

I have a CBFA engine, I'm on Uni Stg2, and in CT. Zero CELs, zero spacers, and zero issues at my last inspection. I'm due later this month, as well.

FWIW I believe the J-Spacer trick is: medium insert on the pre-cat and small insert on the post-cat.

 

[Grabbit]

K04 turbo and corresponding software fixes the CEL.... Just sayin..

 

[JOHNDERS2586]

Problem is most reputable tuners cant or no long choose to mess with emissions related things. It's not like it was before where they just program it to ignore it . With EPA cracking down a lot of these guys will not put things in place to ignore emissions...I've had 3 cars with Cobb AP going back to 2006, the first 2 the Cobb AP could and would ignore 02 code an I could run straight pipe no cat at stg 2 no problem.. Now in 2022 my Cobb Pro Tuner basically said they can't override emissions anymore. An advised a spacer .

 

[gtrude]

Thanks for the responses.

What CEL do you have?

I have a CBFA engine, I'm on Uni Stg2, and in CT. Zero CELs, zero spacers, and zero issues at my last inspection. I'm due later this month, as well.

FWIW I believe the J-Spacer trick is: medium insert on the pre-cat and small insert on the post-cat.

That's good to hear. I've got a Bank 1, Sensor 3 Slow response (P0145) and O2 sensor stuck rich on bank 1, sensor 3 (P2275). I'm at stg2 now...going back tonight to the stock. I'm gonna drive it for a bit and see if they come up again. Weird thing is I was getting it running stage 2, so i'm thinking it could be an actual bad sensor. I may just buy a new one and see how it goes since I don't have the tools or know how to diagnose it any further than that. I've got the urotuning 100 degree(ish) spacer on the downstream sensor, then the other two are just screwed directly into the bung.
I've heard a few variations on what you're suggesting. That's cheaper to try than a new sensor.

CT are bastards about this. Tying this to your registration so you can't put the car on the road (legally). And the $20 cash payment is shady AF...lol

 

[gtrude]

Problem is most reputable tuners cant or no long choose to mess with emissions related things. It's not like it was before where they just program it to ignore it . With EPA cracking down a lot of these guys will not put things in place to ignore emissions...I've had 3 cars with Cobb AP going back to 2006, the first 2 the Cobb AP could and would ignore 02 code an I could run straight pipe no cat at stg 2 no problem.. Now in 2022 my Cobb Pro Tuner basically said they can't override emissions anymore. An advised a spacer .

yeah, shop I was gonna use told me they only do cat-back systems. Some change in state law a number of years back I guess. Apparently I'm commiting some federal offense and didn't even realize it.

 

[BudgetPhoenix]

Thanks for the responses.

That's good to hear. I've got a Bank 1, Sensor 3 Slow response (P0145) and O2 sensor stuck rich on bank 1, sensor 3 (P2275). I'm at stg2 now...going back tonight to the stock. I'm gonna drive it for a bit and see if they come up again. Weird thing is I was getting it running stage 2, so i'm thinking it could be an actual bad sensor. I may just buy a new one and see how it goes since I don't have the tools or know how to diagnose it any further than that. I've got the urotuning 100 degree(ish) spacer on the downstream sensor, then the other two are just screwed directly into the bung.
I've heard a few variations on what you're suggesting. That's cheaper to try than a new sensor.

CT are bastards about this. Tying this to your registration so you can't put the car on the road (legally). And the $20 cash payment is shady AF...lol

IIRC those codes and a few others can pop from simply just bad o2 spacer placement too, depending which bung and their orientation the codes will differ. They will still get rid of the p0420 though

 

[Saabingti]

Thanks for the responses.

That's good to hear. I've got a Bank 1, Sensor 3 Slow response (P0145) and O2 sensor stuck rich on bank 1, sensor 3 (P2275). I'm at stg2 now...going back tonight to the stock. I'm gonna drive it for a bit and see if they come up again. Weird thing is I was getting it running stage 2, so i'm thinking it could be an actual bad sensor. I may just buy a new one and see how it goes since I don't have the tools or know how to diagnose it any further than that. I've got the urotuning 100 degree(ish) spacer on the downstream sensor, then the other two are just screwed directly into the bung.
I've heard a few variations on what you're suggesting. That's cheaper to try than a new sensor.

CT are bastards about this. Tying this to your registration so you can't put the car on the road (legally). And the $20 cash payment is shady AF...lol

Maybe more experienced heads will chime in but since you aren't throwing the P0420 code it sounds to me like your 3rd O2 sensor, the one closest to the rear axle, may be bad. Just so we understand correctly, your current setup from turbo to rear axle is NoSpacer->NoSpacer->Spacer?

 

[BudgetPhoenix]

Maybe more experienced heads will chime in but since you aren't throwing the P0420 code it sounds to me like your 3rd O2 sensor, the one closest to the rear axle, may be bad. Just so we understand correctly, your current setup from turbo to rear axle is NoSpacer->NoSpacer->Spacer?

Not necessarily. As I mentioned in my previous post, the main issue is that the spacers can get rid of the p0420 code but the CEL remains on because the spacers make it throw other o2 sensor codes if they aren't oriented perfectly.

 

[Saabingti]

Not necessarily. As I mentioned in my previous post, the main issue is that the spacers can get rid of the p0420 code but the CEL remains on because the spacers make it throw other o2 sensor codes if they aren't oriented perfectly.

OP could try removing the spacer he currently has installed and seeing if that changes anything.

 

[BudgetPhoenix]

OP could try removing the spacer he currently has installed and seeing if that changes anything.

Yeah that would work to rule out o2 sensor issue. Clear the codes and drive it around a while too after

 

[gtrude]

Maybe more experienced heads will chime in but since you aren't throwing the P0420 code it sounds to me like your 3rd O2 sensor, the one closest to the rear axle, may be bad. Just so we understand correctly, your current setup from turbo to rear axle is NoSpacer->NoSpacer->Spacer?

Yep.

Yeah that would work to rule out o2 sensor issue. Clear the codes and drive it around a while too after

I got impatient and bought a new one. Seems reasonable that it’s bad (car has 140k miles on it) and it was a pretty cheap part.

I’ll put it on tomorrow and see how it goes. If the code’s still coming up then it’s back to spacer arrangements.

 

[gtrude]

Yep.

I got impatient and bought a new one. Seems reasonable that it’s bad (car has 140k miles on it) and it was a pretty cheap part.

I’ll put it on tomorrow and see how it goes. If the code’s still coming up then it’s back to spacer arrangements.

so far so good after getting a new downstream sensor (left the spacer in). I'm 162 miles into the new sensor and all is well. I'm going in for my emissions test tomorrow. wish me luck!