05-18-2018, 02:00 PM | #1 |
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Understanding Datalogs
I know that Datalogs are a vital thing for tuning, and also to asses the general wellbeing of your vehicle.
I've posted several times about my recent BM3 experiences, and I feel like I'm starting to understand things a little more. It's a steep, but interesting and exciting learning curve. I'm not expecting to become a tuner, but I'd like to understand a little more about the various things typically logged in a Datalog, and what conclusions / suggestions you can take away from the data. Some are obvious, and some are not. As far as I'm aware, there is no definitive articles or forum threads on this, so I guess I'm offering to write one and I think everyone in this sub-forum would benefit. Having said that, I'm not an expert by any means, and therefore need some help from others. I'll be updating this first post as more information is added... Let's start: BM3 Default Logged Data Additional Data that can be Logged Datalog Capturing Guidlines In general, datalogs are most valuable if captured during sustained high load acceleration without interference from control systems like stability control, traction control etc.Interpreting Data There are many things to look for within a datalog. Perhaps the easiest way to break this down would be to look at a logged data trace, and its relationship to others at the same time. Please comment if you see any errors, and please add to this post by offering additional explanations. I'll copy your text into the first post and give credit when I do.
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Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings Last edited by Nezil; 05-25-2018 at 01:19 PM.. |
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05-18-2018, 05:56 PM | #2 |
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Reserved in case additional space is needed.
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Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-18-2018, 06:14 PM | #3 |
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STFT is your short term fuel trim - its short term adaptations the ECU is making to the fuel table usually measured in Lambda - usually environmental / different gas / etc etc.
Lambda is your AFR - the proper way to measure AFR is in lambda. |
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05-18-2018, 06:17 PM | #4 |
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Thanks, added and credited!
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2018 ///M2 LCI, LBB, 6MT...
Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-19-2018, 08:46 AM | #5 |
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Nezil, maybe my eyes are failing me, but I dont see an entry in your compilation for LTFT (Long Term Fuel Trim) ? This value is crucial for examining the influence of adaption on your other values and vice versa.
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05-19-2018, 10:43 AM | #6 | |
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Quote:
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2018 ///M2 LCI, LBB, 6MT...
Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-19-2018, 11:20 AM | #7 | |
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In normally aspirated engines, a stoichiometric mixture is one that is 14.7 parts air to 1 part fuel to create the air/fuel mixture (AFR). Obviously, one that has less air is richer and more air is leaner.. .in NA engines, the most power generally occurs when the AFR is a hair richer than stoichio. Now, engines with forced induction require a richer mixture.. Turbos turn up the heat, and a mixture often between 11.5 and 13/1 is required to cool things off and keep knock at bay .. If it runs lean and hot, knock risk increases and timing will be pulled, both of which loses power. So, back to the fuel trims.. The STFT is calculated on a momentary basis and when logging, you will see rapid variations as it shoots high, and then low to dither into the best mix.. Over time, these values get inculcated into the LTFTs through the process known as Adaption. These are useful for diagnostics in that if the trims tend toward too rich or too lean, there could be an issue with various sensors, MAF, O2, or vacuum leaks, or a tune that is not maximized for the conditions. That's basically it at a very high level. There may be some inaccuracies, but in general, thats how it works, at least thats how it did work back about 20 years ago when I was involved.
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'18 LBB MT M2 Exec pkg, Moonroof, Production 7/6/17 Last edited by boostm3; 05-19-2018 at 11:29 AM.. |
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05-19-2018, 11:58 AM | #8 |
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That's perfect, thank you! Any others that you'd like to have a go at? Or corrections to the post as it currently stands?
I'm really hoping this can be a valuable reference to owners of tuned cars that can take datalogs.
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Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-19-2018, 11:59 AM | #9 |
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It looked good to me; really valuable and great of you to post!
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05-20-2018, 01:51 AM | #10 |
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I think I just worked out that Ignition Cyl 1[deg] is a trace of the map's timing target. The Ignition Timing x[deg] traces are for the actual timing for each cylinder.
I'm not 100% sure this is correct, but looking at a number of datalogs, this seems to make sense.
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2018 ///M2 LCI, LBB, 6MT...
Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-23-2018, 11:38 AM | #11 |
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cookiesowns, are you able to provide some help with this thread?
I know you were reluctant to give advise on tuning, but tuning requires an understanding of datalogs, and there is less risk associated with sharing that knowledge, and it's equally, perhaps even more valuable!
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2018 ///M2 LCI, LBB, 6MT...
Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-25-2018, 12:29 AM | #12 | |
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Should include knock sensor voltage Lambda[AFR] - Lambda converted to AFR ( based on gasoline stoich of 14.7 ) ( may be target, or another derived value ) Lambda Act. (Bank 1)[AFR] - Same as above Lambda Control Factor (Bank 1) - Faster[AFR] - Lambda converted to AFR with factor Load Act. (Rel.)[%] - Relative load value in %. 100% means car is hitting load ceiling Load Target (Rel.)[%] - Current Load target % MAF HFM[lb/min] - Mass Air Flow in pounds per minute MAP[psi] - Manifold Absolute Pressure in psi ( actual boost in manifold ) Oil Temp[F] - Oil Temperature in Fahrenheit (or Celsius) Relative Air Filling[%] - Correlate this with MAF HFM. Important to diagnose boost control STFT - Short Term Fuel Trim measured in Lambda credit bovairdf87 Throttle Angle[%] - Angle of the Throttle Butterfly valve in %; not to be confused with Accel. Pedal[%] Vehicle Speed[mph] - Vehicle Speed in miles or kilometres per hour Wastegate Duty Cycle (Bank 1)[%] - Wastegate Duty cycle of Bank 1 ( N55 only has 1 bank ) ( basically percentage of wasgate. 100% means wastegate is 100% closed in general ) Here's a very good simple article of load. http://stratifiedauto.com/blog/load-...-based-tuning/ DME controls boost based on load. This is how it manages torque from the motor.
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Last edited by cookiesowns; 05-25-2018 at 12:34 AM.. |
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05-25-2018, 12:33 AM | #13 | |
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I know that MAF is Mass Air Flow, and is a measure of the amount of air flowing through the intake system, measured before / upstream of the MAP sensor. What I don't know, is what the relevance of this data is. What are you looking for when you read this data, and what are some possible implications. Knock Detected was listed; is Knock Sensor Voltage a different trace? Load I am quite confused about, because the numbers don't seem to be a percentage. I'm not sure what the units are, or what it really means. Torque target must be another trace that's non default, how is this different from Load target?
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2018 ///M2 LCI, LBB, 6MT...
Current Performance Mods: CSF FMIC, ER CP, Fabspeed Cat, Aquamist WMI, GFB DV+, NGK 97506, BM3 (Stage 2 93 OTS), CDV delete, UCP, M2C/M3/M4 Strut Brace, M3/M4 Reinforcement Rings |
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05-25-2018, 12:37 AM | #14 | |
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Yes knock sensor voltage is also a different trace. As I've responded on your other threads, knock sensor is very good to log ( although the accuracy can be debated due to the logging speed ) as it allows you to see "anomalies". Voltage in general should be pretty close together. If it isn't, and you see spikes/dips, that's when you know there is some pinging/knock going on. Torque target is also a non default trace, it is different from load target because torque can be rescaled in the map to get by load/torque limiters in DSC/TCU. Important for 8AT tuners. I like logging this as you can tell if the DME is doing something you don't want it to do. I highly advise you to do some research on load based tuning, as well as general combustion engine principles, as it will really help you with understanding datalogs as well as important/critical values.
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