turbo cruise tuning
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turbo cruise tuning I'm tuning a turbo silverado for speed density and am confused as to how the pcm determines the fuel.
The way I understand it is that during closed loop cruise the VE table provides a fuel amount to send the cylinder and then the O2 sensors measure the result of that combustion and make adjustments to try and maintain 14.7 AFR.
My concern here is that since my engine is turbo charged that while cruising I'm high up on the pressure range of the VE table under light TPS positions. Is the pcm adjusting my LTFT and STFT to try and get to the 14.7? I feel like if I'm close to boost conditions that I should have a richer AFR but am unsure how this accomplished. I don't want the the pcm to try and send 14.7 at 100 kPA as this would be lean.
The way I understand it is that during closed loop cruise the VE table provides a fuel amount to send the cylinder and then the O2 sensors measure the result of that combustion and make adjustments to try and maintain 14.7 AFR.
My concern here is that since my engine is turbo charged that while cruising I'm high up on the pressure range of the VE table under light TPS positions. Is the pcm adjusting my LTFT and STFT to try and get to the 14.7? I feel like if I'm close to boost conditions that I should have a richer AFR but am unsure how this accomplished. I don't want the the pcm to try and send 14.7 at 100 kPA as this would be lean.
Last edited by fire67bird; Jul 27, 2014 at 09:10 PM.
Thread Starter
On The Tree
Joined: Feb 2014
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That is exactly what I was looking for. I was getting hung up on the open loop eq ratio but knew that I was looking for the a closed loop condition to change. This explains why I have been able to get a decent AFR tune at WOT thus far. Now I should be able to get the transition dialed in better by lowing the TPS when it kicks in. Thank You!
Actually, the VE provides an estimated filling of the cylinder against full fill, or higher if in the boost VE table. It calculates how much fuel to inject based on this amount of air in the cylinder and the size of injector.
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Joined: Mar 2010
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My tune was done originally by speed inc around chicago, it was done with no enrichment until 105kpa I think which is the tipping point from vac to positive pressure.
I was wondering what the deal was with that once I started tuning myself. Message a reputable tuner that has had multiple turbo ls setups in varies platforms and he said he always has run 14.7 up until boost without issue.
Retuned my own car like that after I changed turbos and injectors and it runs great. Nice and clean all the way up too boost. The car almost enters BE as it is when I drive with traffic at 30% or less throttle.
I was wondering what the deal was with that once I started tuning myself. Message a reputable tuner that has had multiple turbo ls setups in varies platforms and he said he always has run 14.7 up until boost without issue.
Retuned my own car like that after I changed turbos and injectors and it runs great. Nice and clean all the way up too boost. The car almost enters BE as it is when I drive with traffic at 30% or less throttle.
