Quote:
Originally Posted by arghx7
There's a lot of discussion here among different people and scenarios that I'm trying to unravel.
First question: is this a matter of the fuel trims moving around more than would be ideal or is there an actual driveability, knock, etc problem?
Second: Are we talking about stock port injectors, obviously stock DI injectors, and stock MAF scaling or scaling that has been judged ok before the PI and DI balance was changed?
I suspect there's a bunch of wall wetting compensation, gas flow model, or injector flow compensation that is poorly understood because we don't have actual block diagrams of how the software works, just whatever has been reverse engineered.
My position is, generally speaking and subject to case by case revision--if the fuel trims are just moving around more who cares? That's their job. They're compensating for some inscrutable fuel calculation that hasn't been unraveled, or more likely, production tolerances in injectors, given that the stock values were for some mean spec part most likely.
 Is there an actual problem with the car here or are we just trying to make the fuel trim lines on an excel graph look pretty |
1. Aside from increased LTFT causing the car to run richer than desired OL operation under certain conditions (average to cooler temps) there is not much perceptible drivability issues or increase in knock that I've noticed.
2. I don't think the stock MAF scale has been very good for anyone that I can remember. For my case, it's a maf scale that worked well while running less PI (more like the table below), but experienced a good amount of increase in fuel trims in areas where Port injector ratio was increased. This somehow led to an increase in LTFT in OL operation causing it to run even more rich than before the changes to the port injector ratio tables.
One would suspect one would spend less time "chasing one's tail" if I simply modified the port ratio table to run 100% DI at .20 load and lower, but where is the fun in that right? lol
It's seems that many of the guys that have already done some "tail chasing" had pretty good success balancing the port injectors to the direct injectors after dialing their MAF scale while running 100% DI. This is what I've decided to do now, but I will take it one step further by taking the IAT compensation into account. I've dialed my MAF while running 100% DI at IAT of 66~70*f by making sure my IAT don't go below 66*f throughout the entire range and not using any of the data with intake temps above 70*f. I think this will give me a good base before making changes to the IAT compensation and port injector scaling.
