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Discussion and questions related to the course Practical Reflash Tuning
I am new to tuning and was wondering how much of a difference is acceptable from cell to cell on the ve tables ? any tips on smoothing or interpolating would also be greatly appreciated !
VE values diference in the tune file depend on 2 things- actual engine efficiency and map resolution. Having both of them verying from engine to engine and from ECU to ECU gives you so many combinations that it makes very hard to advise on... In general it can by anything. In reality it shouldn't be too much of the difference but again it depends on map resulting and actual ve at specific rpm.
ok that makes sense but what would you consider to much of a difference ? for instance if the one cell is at 120.0 and then it drops to 91.7 or something far off would that create a hesitation in how the vehicle runs ? like a flat spot in the throttle ?
it depends. If the 120 was at 2000 RPM, and the 91.7 at 2050 RPM, then probably yes. But you would confirm with logging that showed there was a lean spot in the Lambda results around that RPM probably would show up just beyond it due to transport delays in the exhaust system.
Or, are you talking about at the same RPM, so 100kPa is 120, and 95kPa is 91.7 that's not believable, but it's not likely to causing a driving problem.
Please share some pictures of your fuel map so we can see what you are working with. How was the map determined? (dyno steady state, road tuning, provided from somewhere else, some ECU auto-learn, etc)
Here are some tips: For a given RPM, the VE (or fuel pulse width) will only increase or stay the same with increasing manifold pressure (load).
Exhaust and intake system resonances can cause valley's at particular RPMs, often these are very narrow. Many times steady state tuning will produce a deeper valley as it is interpolating to nearby cells that are vastly different, this isn't always seen when accelerating through a specific RPM, so don't hesitate to let's those RPM's run a little rich, you don't need to have a perfectly flat lambda trace to have a good running engine.
If you are going to run steady state at those valley RPMs, then spend the time to tune it the best you can. Don't be afraid to add additional RPM break points in the table to increase the resolution in places where the efficiency is changing rapidly.
i am just asking in general and do not have a map i can share at this time. i am learning how to tune harley davidsons using powervision and the auto tune set up. i am trying not to rely on auto tune though. sometimes after an auto tune run though i will see spikes in the ve map and thats what is concerning me. i see other tuners maps and they look way smoother from cell to cell then the results from the auto tune. so im practicing smoothing and interpolating to try and get a smooth map if that makes sense. part of this question that i didnt state in the initial post, is it more important to get the ve results dead on to the target afr or for the map to be smooth ? i would think they would coincide with each other but being as new as i am i am not sure
The key to using an auto tune feature is trying to run as much smooth steady-state as possible. The longer you "stay on a cell", the more accurate the "average" information of that condition will be. Short runs, running up and down the RPM range can easily result in that "spikey" results you are seeing.
So, lower the spikes, and perhaps raise the VE values slightly at the cells surrounding the spike.
Thank you David. i will keep that in mind on my next tune. i appreciate the input !