Hi , i want swap my 200 cel cat with catbypass in my tuned 996 tt , since i don't want reflash the ecu ( i run very well with my actual program ) i'd like to use an O2 spacer to make CEL light stay off .
So since i've heard that those O2 spacers works well usually but NOT always , i'd like to know in the case they shouldn't do right their job , my only problem should be The CEL light on the dash or if i could have other most serious like fuel trim problems .
Like in the title question is if the ECU use also the post cat O2 sensors signal to correct Fueling / fuel trim or it does not.
Thank you very much

 

post O2 is used for emissions . the light that stays on can be turned off via the dme but passing emissions if required will be an issue. the O2 spacer may work some do some don't. rear O2 shouldn't affect the tune file

 

I know

Do you mean Reflashing the Ecu or just deleting Error code with cable in diagnosis ? And if so , can it be turned off DEFINITIVELY ?

Emissions required , but not an issue passing it ( see my location )

I know

This is the most important and what i was looking for

 

With a stock tune the #2 sensor readings do affect fueling. The DME will adjust fueling to get the readings it expects from the sensors.

What affect installing the 200 cel converters, bypass and the sensor spacers will have on fueling I have no idea. Things may just work out to where the fueling is ok. But maybe not. Ideally the fueling should be checked by instrumentation -- on a dyno with 4-gas analyzer perhaps.

 

its turned off in the computer by your tuner. not exactly a reflash but an adjustment

 

correct

 

i did the same thing, and those 90 angled bung extenders didn't do sh*t. i replaced the pre cats w new, turned off the post cat 02's ( iirc?? ) and no issues. i sure wouldn't roll up to a tester station like that tho...

the sheer joy of elimination the 200 cats though is worth any of the hassle, but those mini cats didn't ( again ) do a dang thing. just gave me cels if memory serves? P0420 P0430 (?!) something like that but thats my failing memory at work.

 

how much could bad o2's affect the injector DC? and is the DME still using these figures to determine fuel t WOT?

 

Yes the post cat O2s do affect fueling, sometimes even on a flashed ecu if you still had cats on that tune.
I found out my car had a mild unknown tune when I bought it since it was hitting 1 bar.
I swapped in a catless exhaust and it ran rich and slower.
Tried mini-Cats which were useless and threw CELs and 90-degree extenders. the 90-degree extenders kept the CEL off for a while but data logging still showed the car running rich. The secondaries weren't seeing enough exhaust.
I got an EPL tune and he "coded" them out, car ran way better, no CEL and good A/F's now.

 

any clue what your injector duty cycle looked before tuning out and after?

Here's what i'm dealing with. Stock tune (99.8% sure) and after my first logging I was in the 100%+ dc range. I replaced fuel filter, that helped a bit, then did the fuel pump and venturi pumps and am now in the 88-90% range. I'm pretty stumped, i've looked over the fuel system,e verything looks proper. Wondering if it's now the sensors.

 

I will check later, I did some logs with an innovative LM2 before the EPL tune but have to look for those files. I don't remember if I selected dc as I had a limited number of values I could record using it. I do remember the Long term fuel trims were 7-10% after swapping in just the catless exhaust.
Since the tune, I picked up a duramtric and pretty sure I had DC in the logs, I emailed them to tony after doing some 3rd gear logs, send me your email and I can shoot them over...

what are your A/F's looking like?