Car is commanding a 12.5 AF before the cats
Car is commanding a 12.5 AF before the cats Would I be safe to try and command 12.8-12.9 to get some more power out of the engine? I believe my car was tuned with a sniffer after teh cats which leans out the reading on the dynojet wideband.
TECH Resident
Joined: Aug 2003
Posts: 970
Likes: 4
From: England UK
Try what works best for your car, somewhere between 12.5 and 13.1. You may wany it richer around peak tq, and lean it out to 12.8 / 12.9 around peak hp.
I've heard a few peoeple mention about the Wideband sensor reading leaner after the cats, but is there proof? how does the extra air enter the system? after the cats?
I've heard a few peoeple mention about the Wideband sensor reading leaner after the cats, but is there proof? how does the extra air enter the system? after the cats?
I think of AFR as just a number are you using in order to make a calculated change. I believe the number on the WB loosely follows what it is in real life. There is error in it. Your WB could say 12.00 but in reality it could be 12.21 if you counted every particle. Just want to tune for max power. Provided you aren't trying to tune for 16 against 1 and run it for long periods of time.
But I guess alot of people shoot for a number. I just wonder if that number equates to the same thing if you tune over a variety of days and the lifespan of the sensor.
But I guess alot of people shoot for a number. I just wonder if that number equates to the same thing if you tune over a variety of days and the lifespan of the sensor.
Teching In
Joined: Sep 2004
Posts: 7
Likes: 0
The cat burns the extra fuel left over from the detenation, that's why it reads differently. The thing is, there is no way to know how effective the cat is doing this. Less fuel, leaner read on the sensor. This is also the reason some people say their car smells like gas when they get rid of the cats.
IF you have a unit that does free-air calibration then sensor drift is inconsequent to some extent. If your wideband relies on the calibration resistor on the sensor, then it will surely drift.
The cat burns the extra fuel left over from the detenation, that's why it reads differently. The thing is, there is no way to know how effective the cat is doing this. Less fuel, leaner read on the sensor. This is also the reason some people say their car smells like gas when they get rid of the cats.
That's really not the case, the sensor doesn't measure fuel content in the exhaust, *ONLY* oxygen. This is why a misfiring engine that pours straight unburned fuel into the exhaust will read lean, because unburnt oxygen is present with that unburned fuel.
I somewhat regularly tune with my LM1 precat (car in open loop) and since I'm on the dyno anyway it either gets one in the secondary spot or the "probe up the butt". Normally they are close, close as in within a few tenths. When I have to pick between one or the other to belive, the nods goes to the LM1 in the pre-cat bung over the pipe insert unit for the dyno.
Teching In
Joined: Sep 2004
Posts: 7
Likes: 0
That's really not the case, the sensor doesn't measure fuel content in the exhaust, *ONLY* oxygen. This is why a misfiring engine that pours straight unburned fuel into the exhaust will read lean, because unburnt oxygen is present with that unburned fuel.
I somewhat regularly tune with my LM1 precat (car in open loop) and since I'm on the dyno anyway it either gets one in the secondary spot or the "probe up the butt". Normally they are close, close as in within a few tenths. When I have to pick between one or the other to belive, the nods goes to the LM1 in the pre-cat bung over the pipe insert unit for the dyno.
I somewhat regularly tune with my LM1 precat (car in open loop) and since I'm on the dyno anyway it either gets one in the secondary spot or the "probe up the butt". Normally they are close, close as in within a few tenths. When I have to pick between one or the other to belive, the nods goes to the LM1 in the pre-cat bung over the pipe insert unit for the dyno.
Last edited by jsk96z28; Apr 8, 2008 at 06:11 PM.
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