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      05-18-2018, 02:00 PM   #1
Nezil
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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
  • Accel. Pedal[%] - Position of the Accelerator Pedal in %; not to be confused with Throttle Angle[%]
  • Ambient Pressure[psi] - The current ambient air pressure in psi
  • Boost (Pre-Throttle)[psi] - The current intake manifold pressure in psi
  • Boost pressure (Target)[psi] - The boost pressure being targeted by the DME map in psi
  • Coolant Temp[F] - The coolant temperature in degrees Fahrenheit (or Celsius)
  • Engine speed[rpm] - The spped of the engine in crankshaft revolutions per minute
  • Gear Actual - The transmission gear currently selected
  • HPFP (Target)[psi] - The High Pressure Fuel Pump pressure being targeted by the DME map in psi
  • HPFP Act.[psi] - The High Pressure Fuel Pump actual pressure in psi
  • HPFP Act. (Raw)[psi] - The raw data of the High Pressure Fuel Pump actual pressure in psi
  • IAT[F] - The Inlet Air Temperature in Fahrenheit (or Celsius)
  • Ignition Cyl 1[deg] - The timing advance (or retard) target in degrees before TDC
  • Ignition Timing 1[deg] - Timing advance (or retard) for cylinder 1 in degrees before TDC
  • Ignition Timing 2[deg] - Timing advance (or retard) for cylinder 2 in degrees before TDC
  • Ignition Timing 3[deg] - Timing advance (or retard) for cylinder 3 in degrees before TDC
  • Ignition Timing 4[deg] - Timing advance (or retard) for cylinder 4 in degrees before TDC
  • Ignition Timing 5[deg] - Timing advance (or retard) for cylinder 5 in degrees before TDC
  • Ignition Timing 6[deg] - Timing advance (or retard) for cylinder 6 in degrees before TDC
  • Knock Detected[0/1] - Information on if Knock has been detected by the knock sensor
  • LPFP Act. (Raw)[psi] - The raw data of the Low Pressure Fuel Pump actual pressure in psi
  • Lambda[AFR] - [Lambda converted to AFR (based on gasoline stoich of 14.7), may be target, or another derived valued. credit cookiesowns
  • Lambda Act. (Bank 1)[AFR] - Same as Lambda[AFR] credit cookiesowns
  • Lambda Control Factor (Bank 1) - Faster[AFR] - Lambda converted to AFR with factor credit cookiesowns
  • Load Act. (Rel.)[%] - Relative load value in %. 100% means the engine is hitting its load ceiling credit cookiesowns
  • Load Target (Rel.)[%] - The current load target credit cookiesowns
  • MAF HFM[lb/min] - Mass Air Flow in pounds per minute
  • MAP[psi] - Manifold Absolute Pressure in psi
  • Oil Temp[F] - Oil Temperature in Fahrenheit (or Celsius)
  • Relative Air Filling[%] - ???
  • 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)[%] - Percentage of Wastegate actuation; 100% usually means that wastegate is fully closed credit cookiesowns
Additional Data that can be Logged
  • LTFT - Long Term Fuel Trim measured in Lambda credit boostm3
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.

A dyno capture is ideal, but often impractical and expensive, so many logs are captured on the road. In these cases the most common gear to use is 3rd, as a compromise of the speed reached by redline in this gear, and the duration (and therefore data points) required to get there. DSC Off should be selected. Try to capture logs from 2,500rpm up to redline at Wide Open Throttle (WOT).
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.

IAT
As the turbo charger compresses air, the temperature of that air increases. This has a negative impact on the combustion process, and can contribute to the onset of pre-ignition or knock. The Front Mounted Intercooler (FMIC) on our cars is intended to reduce the temperature of the compressed air, but is considered slightly undersized for our cars.

In a datalog, you would typically see the IAT temperature rise during a hard pull, and then provided the car is moving, and therefore ambient air flowing over the FMIC, the temperatures should drop when coasting or cruising. It is not unusual to see the IAT increase when stopped, because no air is flowing over the FMIC and the FMIC is mounted close to the hot radiator.

One thing to look for in the datalogs, is if the increased IAT is causing the engine to reduce power. Look for reduced timing advance when comparing two pulls with different IAT levels. If the timing advance is reduced when the IAT increases, it would be worth looking at your FMIC setup to see if there is anything that can be done to improve the situation.
Timing
Timing can be one of the most useful indicators of engine optimisation. In basic terms, advanced timing (starting the ignition process before the piston reaches top dead center) can improve performance and / or economy and / or emmisions. Retarded timing (starting the ignition process after the piston reaches top dead center) can create burble sound effects.

Very advanced timing is often used when not much power is required from the engine, such as when cruising or coasting. Under heavy load however, very advanced timing can cause pre-ignition or knock. This is where the air fuel mixture, rather than burning cleanly as a controlled flame front starting from the spark plug and progressing through the combustion chamber, instead ignites in multiple unpredictable places around the combustion chamber. Knock is bad for engines, and can be prevented by reducing the timing advance so that the spark starts combustion later in the cycle, at the expense of torque.

As you look at the datalogs, ideally you should see your timing consistent across all 6 cylinders, and maintained throughout the rev range and throughout the pull. If the timing of all cylinders deviates significantly, or the overall timing drops unexpectedly, this is a sign of the engine protecting itself and therefore reducing power.
STFT & LTFT
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. credit boostm3
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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      05-18-2018, 05:56 PM   #2
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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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Quote:
Originally Posted by bovairdf87 View Post
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.
Thanks, added and credited!
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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:
Originally Posted by boostm3 View Post
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.
Thanks boostm3, would you be able to explain how you would use this trace and what it's implications are, similar to what I've written for Timing and IAT. I've added the item to the first post and credited you.
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      05-19-2018, 11:20 AM   #7
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Quote:
Originally Posted by Nezil View Post
Thanks boostm3, would you be able to explain how you would use this trace and what it's implications are, similar to what I've written for Timing and IAT. I've added the item to the first post and credited you.
Sure, Ill take a crack at it, although I may be a little rusty since its been years since Ive been directly involved with tuning using it.

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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      05-19-2018, 11:58 AM   #8
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Quote:
Originally Posted by boostm3 View Post
Sure, Ill take a crack at it...
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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      05-19-2018, 11:59 AM   #9
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Quote:
Originally Posted by Nezil View Post
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.
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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      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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      05-25-2018, 12:29 AM   #12
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Quote:
Originally Posted by Nezil View Post
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!
What exactly do you want help with.

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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Quote:
Originally Posted by cookiesowns View Post
What exactly do you want help with.

I don't see MAF HFM lb/min being logged/referenced as well as the knock sensor voltage. Another very good log value is load actual, target, as well as torque target.
Well some explanations on those things.

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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      05-25-2018, 12:37 AM   #14
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Quote:
Originally Posted by Nezil View Post
Well some explanations on those things.

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?
I responded above. ( updated )

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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