Third O2 on the V6, can it be disabled for tuning?

[guardsman01]

Hey Chris, Keith, or Ken,
Can we disable the third (after Cat) O2 on the V6s for tuning purposes......thinking about it, that O2 will skew the true readings from the engine.....

Or would it be better to just leave it in the loop, since it would change things when it was plugged back in?

Thanks. John

[arthansen]

You do not need it! You can take it out of the car if you wish or leave it in. It does nothing except test your Cat and throw a code if it sees a problem. It has no effect on performance. Just change all these codes to SES Enable "Off" and "No Error Reporting".

137
138
139
140
141

Good Luck.

p.s. Of course, this would only be true for "Off Road Use".

[guardsman01]

I commute with my car, so I don't want to remove it completely (risk destroying the cat - $$$$$$$), but I'm just wondering if it would be benficial to do the VE tuning without it in the loop.

And, of course, EVERYTHING I do to my car is COMPLETELY legal....... 8)

[arthansen]

The rear O2 won't save your cat, it will just tell you when it is gone. However, if you have your stock cat, just leave it alone. It will not effect your tuning at all.

On my car, the cat developed a 3" hole right through the middle of it (very strange) so I had to take the rear O2 out to keep it from getting hurt. You obviously have not had this strange phenominom effect your cat so just leave it alone and tune away.

[FastFieros]

The rear O2 won't save your cat, it will just tell you when it is gone. However, if you have your stock cat, just leave it alone. It will not effect your tuning at all.

On my car, the cat developed a 3" hole right through the middle of it (very strange) so I had to take the rear O2 out to keep it from getting hurt. You obviously have not had this strange phenominom effect your cat so just leave it alone and tune away.

This is correct that the rear O2 is for reference only. The PCM see's the signal and does a compare to a table. When it exceeds the table parameters it throws the code for CAT failure.

Turn off the code with the DTC tool.

Loyde

[guardsman01]

But I thought that it was also involved in closed loop fueling......

I understand that it will throw the code code if the difference between the pre-cat O2s and the after-cat O2 gets too big, but I thought that the PCM also used the after-cat O2 to adjust the trims, in order to keep the AFR in the proper range for the cat?

[FastFieros]

But I thought that it was also involved in closed loop fueling......

I understand that it will throw the code code if the difference between the pre-cat O2s and the after-cat O2 gets too big, but I thought that the PCM also used the after-cat O2 to adjust the trims, in order to keep the AFR in the proper range for the cat?

I have the GM video on EFI controls. It indicates no driveablity change in PCM parameters. The video was made in 96 however, and things change every year and with every model of car seems like.

I can tell you from experience of installing over 20 3800SC V6 engines in Fieros and taking the 2nd O2 out of the system and deleteing the codes via HPT, that they all seem to run fine. LTFT changes with MAF and IFR... Dont see it change with 2nd O2 off or on....

Loyde

[guardsman01]

Cool, thanks