Will O2 sims correct an over-rich condition at high revs/loads

[RockyTop]

I have very hi-flow through cats (the biscuit is gone in one and perhaps the other). I set no codes unless an 02 sensor is going bad (usually a front one). Nevertheless, I wonder if 02 sims would be a good idea in light of my nearly cat-less exhaust.

Can some on here bring me up the learning curve ?

 

[ewave]

No, O2 Sims will not correct your rich condition at WOT. Sims only make the PCM THINK that there are cats installed and working correclty. It will prevent the check engine light from comming on.

BTW not all check engine lights cause "limp home mode". A failure of a cat or the skip shift will not casue limp home mode. Limp home mode is triggered by detection of a failed sensor that is used to set FA ratio.

 

[Jack B]

Rocky Top:

The 97 PCM should not give you a problem. Many 99 and earlier cars are running catless (myself included) without any problems. I have numerous dyno pulls that include a/f. When I run on motor the a/f is the typical stock viper semi-lean (13-14) condition.

 

[RockyTop]

Thanks all for the input. It's time to get to the dyno and see what's up with rwhp, air/fuel, etc. The reason that I post is that in the heavy braking zones I am puffing blackish smoke which to me indicates rich condition. I undoubtedly must also have the oil puke in the air box thing going on as do all agrressively driver snakes. I get a lot of blackish sluge on the rear of my car just above the exhaust tips, etc. Feels oily to me so I have to think that my car is puking oil and ingesting it. Hopefully its not [just] attributable blow by as it is farily substantial. Further thoughts?

 

[RockyTop]

Ewave, I typically only the smoke under heavy decel at the track. Does this change your conclusion ?

 

[ewave]

There will always be a check engine light on when the car is in limp home mode. Basically the PCM figures out there there must be a malfunction with a sensor, so it goes to the most conservative guess at fuel and spark advance to minimize possibility of damage to your engine. This usually means running rich, and with lots of retard. Doing this for extended periods of time could damage a cat if way too much fuel is being dumped into it.

If you don't have a check engine light on, then your car is NOT in limp home mode, and the PCM is trying to do its best to set FA and timing for maximum performance.

Because the car has no knock sensor, the PCM has to be a little careful with FA and timing. The Stock (and Mopar) PCM are designed to run slightly rich. While not giving you maximum HP, running slightly rich has a lower risk of detonation... This is because rich conditions run slightly cooler than lean conditions... When you get things too hot in the cylinders and pistons, the extra temp contributes to detonation. When this leads to pre ignition you're phucked.... 1 second of pre ignition will destroy an engine....