Discussion and questions related to the course Ethanol & Flex Fuel Tuning
As one moves from a good tune using Race gas (e.g. Sunoco GT 260 100 octane unleaded), to say a blend of that race gas and E85 to get to E50, I notice that the transient fueling is off now. For example, throttle tip in is a bit lean (1.15 lambda) and when letting off throttle, a lean spike happens as well (get a lambda of 1.18-1.20 briefly. Using a GM 3rd gen LS PCM and HP Tuners, there are several tables on transient fueling including fuel-to-wall impact, impact gain, and boiling time. It seems to me the properties of ethanol are different than race gas where it likely is sticking more to the port walls and doesnt evaporate as quickly off the port walls, causing the transient fueling lean spikes. Question is, what tables to I modify to correct the situation. My inclination is to increase the boiling time (maybe 20%) table and see if that fixes it. The Fuel-to-wall impact factor table, from what I understand, has an effect not only at a given MAP (kpa) (I am SD tuned), but also the magnitude of MAP transition (for example going from 30kpa to 95 kpa vs 30 kpa to 50kpa). Any insight would be welcome. Thanks in advance for any info.
Hi Alex you can give your idea a go and see if it works but most guys I have talked to up the PE to about 1.33 from 0-1500 unfortunately it will make the pump gas tune accel rich as but you will most likely have to compromise somewhere, another post I have read suggested to Try adding to the transient fuel mass impact tables. I am not familiar with doing this myself sorry
Yeah, I don't want to just rape the PE.
Also, the lean spikes happen outside of power enrichment as well. So for my PCM (Gen3 LS), if the STFTs are reading real lean when going into PE, the PCM will add a ton of fuel, giving inconsistent PE AFR ratios.
Just looking for someone who has experienced this, as I imagine it occurs