What do the front 02's do? What do the rear 02's do?

Why do we use sims for the front 02's?

Are the 02's on a LT1 the same or different than the LS1's?

Thanks for your help.

Coach

 

I thought we used the sims in the rear ONLY after the cats are gutted or removed!?

 

Front O2s watch and measure oxygen coming out of the motor. They also help in the misfire tests.

Rear O2s watch what happens to the gases after they pass the catalytic converters.

The O2s on an LT1 are different (err, at least OBDI LT1's, not sure about OBDII).

You can use simms on the rears, but not the fronts. The PCM is really just watching the signal from the rears to make sure that they are transitioning across .45 volts (which is 14.7:1 AFR). The simms just sit there and toggle up and down around this voltage.

If you're running open loop, front O2s are ignored.

If you're at full throttle, front O2s are ignored.

If you're at partial throttle, front O2s measure oxygen content, and the fuel trims are updated correspondingly (rich / lean trends). PCM adjusts injector pulsewidth based on this info.

Fronts do all the work. Rears are... Optional.

Andrew

 

Thanks, Andrew!!!!!!!!!!!!!!!!!

Coach

 

the thing with the rears is for the obd2 testing. i had my rear o2's deleted from the computer and it passed inspection, in the computer at least. like he said they should read about .450 and thats a legal for passing emission testing. but pretty much the rears are there for cars who need state inspections and they read off the o2's now instead of the sniffer, on the 96 and up cars. anything older than 96 has one o2 before the cat to just monitor the engine and how rich/lean it is running. there is not one after the cat becasue it is obd1 and requires a tail pipe sniffer test....here in NC at least

 

I plan on running Cats with my LT's. Can I run without the rear O2's? I would have them deleted in EDIT. Or is it best to use them?

 

You can run with rear 02's and CATS with LT headers.
I am doing it now.

 

In Australia all LS1s run cats but don't run rear O2s.
In New Zealand even the cats are optional (although that may change soon).

Paul

 

So what is the point of running the rears? Emissions?

 

The post cat LT1 02's are the same part # as the pre and post cat LS1 02's. A friend bought the wrong ones for his LT1 (rear instead of front) and they were the same # as mine.