Long tubes and CELs - help me understand

[gahammerle]

It seems like all the LTs eventually throw the CEL because the post-cat O2 sensor. From pics I've seen of some of the LTs, it looks like the pre-cat O2 sensor is in one of the tubes rather than in the collector or farther down-stream. Does this mean the pre-cat sensor is only sniffing 1/3 of the exhaust but the post-cat sensor is sniffing 100%? If the pre-cat sensor was moved to the collector or just before the cat, would that eliminate the CEL since both the sensors would then be sniffing 100%? Or does the O2 sensor measure a ratio rather than volume?

[Ivan @ Southwest Speed]

Originally Posted by gahammerle

Does this mean the pre-cat sensor is only sniffing 1/3 of the exhaust but the post-cat sensor is sniffing 100%?

In theory, yes. Since it is only exposed to the first "percentage or fraction" of the system, then in theory, it can only report that information.

Originally Posted by gahammerle

If the pre-cat sensor was moved to the collector or just before the cat, would that eliminate the CEL since both the sensors would then be sniffing 100%?

No. There are perameters, or sets of numbers, that the two sensors' readings must fall into to prevent a CEL initiation. If the readings are out of the specifications set forth by the "engineers" at GM, then the trigger is sent to turn the condition on.

Originally Posted by gahammerle

Or does the O2 sensor measure a ratio rather than volume?

It actually reads differences in exhaust gas and the "reference air" and that is transduced into voltage for the system to measure and determine if it is within specifications mentioned above.

Clear as mud?? LOL... It takes some getting used to and people get paid more money than I'll ever see to make sure it's not simple to cheat or manipulate easily.

Hope this helps a little.
-Ivan @ Southwest Speed

[usa1camaro1969]

My question then is how are some able to address it with the spacers? Is there a lot more power to be had with the long tubes verse the shorties?

[KMPrenger]

I don't know of anyone yet that can 100% say they cured the problem with 02 spaces on their LT setup. OUR BEE has been trying it out, but I'm pretty sure he got a CEL even with 2 spaces on each sensor. They seem to help though.

and yes, LTs will likely give you 75 to 100% (double) the power of a shorty setup. But then you get to deal with the CEL issue, and hope you can handle the new noise lol.