lean A/F on trans-brake

[quickstrike]

I have been noticing a lean spike for the 1-2 seconds the car is held on the transbrake/2 step rev limiter.

Is this a normal condition, due to the unstable condition the motor is in. I figured since spark was being pulled out by the revlimiter, that it would cause an overly rich condition for a couple seconds but it doesnt seem to work that way.
I should mention that I have my closed loop set to come in at 500 RPMs above the launch RPM, and this is verified because I have no O2 correction untill I launch.
I have changed the VE numbers a little, but it doesnt affect it a great deal. It is spiking to about 15-1 on TB, and it makes me very nervous to see that on a data log.
Can I maybe pull alot of timing out in these cells, to help? Maybe the o2 readings are not accurate at this point?

I have even been told of people somehow using the nitrous controller function during the TB launch, to force an A/F ratio. This baffles me.

Any tips on best way to tune for a good TB launch would be appreciated. Car is running quite well in all ranges of RPM.
P.S. Love this forum!........You GM guys are ok!
Randy

 

[TurboTR]

Well the sensor doesn't read fuel, it reads O2 basically. So if you send several cyls worth of raw uncombusted air down the exh every couple of revs that's just what you might expect to see IMO.
If you are in open loop anyway at that point then the lean spike from the misfires won't be "winding up" the closed loop control. Sounds like it's working right to me, and the approach you're taking is good.

TurboTR

 

[Craig Smith]

Being on a rev limiter basically removes the validity of any O2 sensor reading. The "garbage in, garbage out" theory applies here. The airflow signal being applied to the sensor is not one that is representative of how the motor truly runs. This is to be expected. If you have the areas around that point well tuned, it's really all you can do.

 

[quickstrike]

Thanks guys I will tune those cells without the transbrake on and it should be fine during the TB time. ie: same boost and rpm point............

I wont worry about it then. Its just a little un-nerving to see that big old lean spike.

Randy