02 simulator question

[97ss497]

I'm trying to understand what O2 sims do as far as relaying fuel/air mixture back to the PCM. I'm installing a Random Tech dual cat y-pipe and headers on my 97 SS, and was wondering if replacing the stock after cat 02 sensors with 02 sims would be of any benefit. Does an 02 sim relay back to the PCM that the air/fuel mixture is at perfect nominal conditions? Would there be any negative effects of adding 02 sims?

[97ss497]

ttt

[fastTa]

I will do my best to explain this, bear with me.

The "pre-cat" o2 sensors measure the air / fuel ratio coming through the exhaust manifolds. These provide the PCM with accurate data to enable correct fuel trim as well as the proper fuel tables.

The "post cats" have nothing to do with the fuel management but simply provide the PCM with the info on the efficiency of the catalytic converters to store or trap oxygen. Since oxygen sensors read low voltage when they sense oxygen, and high voltage when there is a lack of oxygen, you would see a high voltage reading on the rear or post catalytic O2 sensors with a good converter because it has absorbed the oxygen in it's effort to clean the exhaust.

So basically the "post cat" o2 sensors" make a comparitive reading to the "pre-cat" o2 sensors" regarding the oxygen concentration respetively within the exhaust stream.

So in essence the rear o2 sensors are there to simply warn you about an SES warning light/code that your cats are no longer storing oxygen properly.

So an 02 sim fools the PCM into thinking your cats are working just fine!

Just for tuning reference if you were interested, if you are running pump gas the IDEAL air/fuel ratio is 14.7:1. This is 14.7 pounds of air to 1 pound of fuel. This is also referrred to as a "Stoichiometric Mixture".

Hope I helped and didn't confuse you

[Joe 1320]

Re: 02 simulator question

Originally posted by 97ss497
I'm trying to understand what O2 sims do as far as relaying fuel/air mixture back to the PCM. I'm installing a Random Tech dual cat y-pipe and headers on my 97 SS, and was wondering if replacing the stock after cat 02 sensors with 02 sims would be of any benefit. Does an 02 sim relay back to the PCM that the air/fuel mixture is at perfect nominal conditions? Would there be any negative effects of adding 02 sims?

The 02 sims have been covered, but there is something to watch out for. Some cars seem to throw a low EGR flow code when the cats are removed if that is your plan. It appears that backpressure in the exhaust system is responsable for aiding the flow of the exhaust gasses through the EGR and it only seems to affect dual cat OBDII cars. The two ways around this are simply re-installing the cats or a new computer program with EGR delete.

14.7 to 1 is an ideal cuising ratio for economy, but not for maximum power. Depending on the motor setup, 11.8-12.8 to 1 is typically the range that you'll see performance increases. Too lean, and power drops off due to knock. Too rich, power drops off and it also may knock.

[97ss497]

Thanks Kevin! Thats exactly the info I was looking for. Thanks too Joe; and yes I will have brand new Random Tech cats on my y-pipe so an EGR fault should not be an issue.

Brian