N54 JB4 Data Logging Guide

BMW N54 Ultimate Data Logging Guide – JB4 Data Logging

About Zach Mayock - DieselIQ

Meet Zach

Zach is a BMW enthusiast with a passion for performance. With over 10 years of experience modifying and performing DIY work on BMWs, he’s developed a deep understanding of virtually every BMW engine. He’s also the proud owner of a 600whp N54 with upgraded twin turbos and an E30 325i drift car and has a particular affinity for the S58 engine. Zach is highly knowledgeable about all things BMW, but his expertise in tuning and performance mods sets him apart. His experience as an enthusiast, combined with his technical knowledge, makes him an essential resource for anyone looking to improve the performance of their BMW.

We recommend Burger Motorsports JB4 tune not only as an excellent stand-alone tune, but also for its advanced safety, boost control, and data logging. The JB4 works wonders whether you are running the JB4 as a stand-alone tune or coupling it with a back-end flash tune. Data logging is essential to ensure your tuned and modified BMW N54 is running well. However, data logging may look complicated and overwhelming at first sight. With so many parameters where do you even start? In this post, we will discuss setting up your N54 for data logging, examining the various parameters, and highlighting examples of data logs with useful tips.

Setting up BMW N54 JB4 Data Logging

  1. Install JB4 tune
  2. You must have a wired BMS Data Cable or Wireless Connection Smartphone Kit
  3. Install JB4 mobile app
  4. Ensure you are running the most current JB4 firmware
  5. Launch the app and connect to JB4

Another important step prior to data logging is enabling 6-cylinder timing mode. This will show individual cylinder timing and assist in tracking down any potential issues. However, there are a few steps to enabling 6-cylinder timing.

Setting up N54 JB4 6-Cylinder Timing

Prior to setting up 6-cylinder timing you must determine your ECU/DME model. Typically N54s built prior to mid-2008 will have the MSD80 (I8A0S). Models built after mid-2008 typically feature the MSD81 (IJE0S). There are a few ways to determine your DME:

  1. Use MHD app and plug KDCAN cable into OBDII port. The MHD app will clearly display whether you have an I8A0S or IJE0S DME.
  2. Check your DME directly. The DME will indicate MSD80 or MSD81.

Once you determine the correct DME, move onto the following steps:

  1. Launch JB4 app and connect
  2. Go to “Settings” tab and click into “User Adjustment”
  3. Scroll down and locate “6-Cyl Timing Setting”
  4. Input 4 for I8A0S or 5 for IJE0S, as stated just below the setting

How to Data Log with N54 JB4

Starting the data log is pretty self-explanatory. On the “Display” tab of the JB4 mobile app, you will see a large green button that states “Start Logging”. However, there is one additional tip to note. Back in the “Settings” tab, you will find the option to click on “Logging Settings”. Contained within you will notice an option “WOT Autolog Threshold (Pedal)”. You can set 80%, for example, and the JB4 app will automatically begin data logging when you are connected and the pedal position exceeds 80%. This may be a useful option for those who want to keep their eyes on the road rather than fumbling around with their phone to begin data logging.

Now that your settings are in place we will move on to how you should data log. You want as much information as possible within the data log, including an overview of as much of the RPM range as possible and a gear shift. Therefore, typically the best way to log is as follows:

  1. Fully disable traction control
  2. Start in 3rd gear and go WOT around 2000-2500 RPM’s
  3. Pull through entire gear (at least 6000+ RPM’s)
  4. Shift into 4th gear and remain WOT for at least a couple seconds
  5. Let off and end log

*Consider logging at least a few runs while you are out

**While you can data log on any JB4 map, there are some benefits to logging Map 1 or 2

One caveat we forgot to mention before. Unless your N54 has some odd gearing you’re likely doing 90mph+ by the end of the data log. As such, you may consider renting an airstrip. Of course, the drive from Colorado to Mexico is beautiful so we tend to opt for the latter.

How to View Your JB4 Logs

Once you have your logs you should e-mail the .csv files to yourself. We prefer to view the .csv logs directly, however the logs may look a little intimidating at first. You may opt to use a website such as datazap, which will graph the logs for you and you can choose individual parameters or a group of parameters to view. We found datazap useful when we were first learning. Additionally, we will use some screenshots of Datazap logs throughout the post to discuss the various parameters.

Another option, and the one we will use most frequently throughout this post, is to install the JB4 interface on your computer. This may be found at the below link:

JB4 Interface Download & Instructions

BMW N54 JB4 Data Logging Parameters

What are all of the data logging parameters? What do the logging parameters mean? Holistically observing a log and coming to a proper conclusion may be overwhelming at first – at least it was for us. Worry not, though. We will break down all of the various parameters with descriptions and examples of each.

N54 used for Datalogging:

2007 335i AT w/ 113k miles

JB4 only in lower boost logs. JB4 + MHD Pump Gas back-end flash in higher boost logs

25-40% E85/91 octane

VRSF Catless Downpipes


MMP Stock Location Inlets/Outlets

XHP Stage 3 Transmission Flash

*Going from left to right on .csv file.

**Values at top of spreadsheet are at the bottom of this post


A rather unimportant data point, the timestamp represents time in tenths of a second (.1 seconds). Therefore, a timestamp of 10 equals 1 second. The JB4 also calculates MPH, so the two may be used in conjunction to estimate your N54’s 0-60, 0-100, and 60-130 times (or whatever speed you choose to measure).

Data Logging Timestamp

Here we see the N54 reach 60mph at a timestamp of 24.75 and 100mph at 81.5. We can then calculate the 60-100mph as: 8.15 – 2.475 = 5.675 seconds.


Engine speed measured in revolutions per minute.


ECU_PSI is boost pressure (psi) as observed by the ECU. This is not the actual boost pressure, but rather the JB4 alters ecu_psi to control the throttle blade.

**DME (Digital Motor Electronics) and ECU (Engine Control Unit) mean the same thing – the N54’s computer.


The PSI the JB4 is targeting. Actual boost should remain within roughly +/- 1psi of target. Boost over-target likely indicates a tuning issue that should be addressed. More frequently, the N54 will see issues with boost under-target. Often times, under-target boost represents a boost leak. However, N54’s on old OEM turbochargers with frequent under-target boost may suggest the turbos are simply tired.


Actual boost (psi)  as measured in the chargepipe before the throttle body. The OEM N54 TMAP sensor is only able to read boost up to 20psi. A 3.5 bar TMAP sensor is required for boost above 20psi and up to 36psi. Maps 1, 2 and 5 are most common on bolt-on N54’s; map 1 will target 13psi peak, 14.5psi for map 2, and map 5 will target 12-17psi depending on mods, fueling, and conditions. Map 7 requires straight 100+ octane race gas and will target 18.5psi peak. Boost should taper a few psi moving towards the top-end. The exact amount of taper depends how aggressive you are running the turbos. A 10psi peak target will generally taper less than an 18psi peak boost target.

More aggressive boost targets will require a back-end flash tune. Generally, we recommend keeping stock turbos under 17-18psi if you are on stock inlets and outlets. With upgraded inlets/outlets, we recommend pushing no more than 20psi peak. Anything over 18psi without inlets/outlets, or 20psi with them, is beginning to push the stock turbos well outside of their efficiency range. This will put additional stress on the turbos with minimal performance gains.

Boost vs Target

The above log shows a standard boost-curve for stock turbos. This N54 is targeting 15psi on the low-end and mid-range with some minor overboost to 15.8psi. Target boost tapers to about 12.5psi on the top end and the turbos are under target by about 0.5psi. This is pretty normal boost as it remains within +/- 1 of target.


Pedal position measured from 0-100%. 100% pedal input is typically referred to as WOT (Wide Open Throttle).


Intake air temperature as measured by the TMAP sensor. The stock N54 intercooler typically results in IAT temperatures 20-40°F above outside air temperatures. WOT pulls through multiple gears cause IAT’s to jump 60-100°F above outside temps. IAT’s increase at idle (especially after spirited driving) and in boost. Lightly accelerate from a red light or cruise at constant speed and IAT’s should drop back to 20-40°F above outside temps.

The below graph demonstrates an N54 with a stock intercooler running in ambient temperatures of 30°F. This pull begins in 3rd gear at ~2850rpms, shifting to 4th at 6850rpms, and ends just after 100mph.

N54 IATs

IAT’s start at 69°F, or roughly 39°F above ambient temperatures. This N54 was heat-soaked from multiple 2nd-4th gear pulls prior to the above log, which is why IAT’s already began on the higher end. By the end of the pull, IAT’s reach 132°F. An upgraded FMIC comes into play as an important supporting mod at higher than stock boost.

Larger and more efficient aftermarket intercoolers keep temperatures significantly lower than the OEM FMIC. High quality FMIC’s keep the N54 IAT’s to roughly 5-15°F above ambient temps. However, the most noticeable difference is during multiple gear pulls; upgraded intercoolers should keep IAT’s down to only 20-30°F over outside temperatures. Additionally, running meth injection may enable the N54 IAT’s to drop below ambient temperatures; though meth injection comes with its own risks.


Measures the amount of fuel added, from 0-100%, through port injection. This value should always read 0 if you are NOT running port-injection.


Waste-Gate Duty Cycle as measured from 0-100%. The turbocharger waste-gates are responsible for diverting exhaust flow around or into the turbochargers. As the waste-gate closes, more exhaust flow is directed to the turbine. The N54 waste-gates are controlled by vacuum and waste-gate solenoids (AKA pressure converters or boost solenoids). Vacuum is applied to the waste-gate actuators thereby allowing the waste-gates to open or close. 0% WGDC means the waste-gates are completely open and allowing minimal or no boost. 100% WGDC means the waste-gates are completely closed allowing maximum exhaust gas airflow through the turbine and maximum boost.

High waste-gate duty cycles of 80%+ are normal when the turbochargers are building boost. All else equal, higher WGDC during spool will cause the turbochargers to spool faster. The more exhaust flow you force into the turbine, the quicker you are going to build boost. As boost nears and reaches target the WGDC’s should drop to the ballpark of 30-75%. This may vary quite a bit between each N54 as boost targets and other factors greatly influenced WGDC. For example, running stock boost at ~8psi should result in lower WGDC as compared to the same stock turbos at 18psi. This makes sense given you need to flow more exhaust gases through the turbine to run higher boost. In order to flow more exhaust gases (again, all else equal), the waste-gates must close further (higher WGDC).

For the most part, WGDC is unimportant unless:

  1. Is WGDC consistently high? Is boost also under target or taking unusually long to reach target?
    1. Indicates a potential boost leak. Remember from above, boost pressure is measured in the chargepipe just before the throttle body. As such, a boost leak will cause a lower boost reading even though boost (if measured at the turbo outlets) is actually on target. It is extremely important to be on the look out for any potential boost leaks, especially if pushing OEM turbos towards their upper limits at 18+psi. It is possible to overspin your turbos with a boost leak when you are targeting aggressive boost.
  2. Is WGDC too low? Is your N54 also making minimal or no boost?
    1. Indicates potential waste-gate solenoid problem or failure (boost solenoid) or vacuum issue. If vacuum is not applied or the solenoids are not functioning properly then the waste-gates will remain open and build minimal boost.
    2. Additionally may indicate an actual waste-gate issue. N54 waste-gates are designed to fail in the open position and will not build boost.


Position of the throttle blade as measured from 0-100%. WOT (100% pedal input) on the N54 should result in throttle values of 90-100% when boost is on target. Typically the value will remain pinned at 100%.


This value represents the fuel pressure supplied from the N54 high-pressure fuel pump. The JB4 actually generates the HPFP pressure by reading the voltage of the pump. Each unit of measure is equivalent to roughly 150psi. Therefore, a reading of 10 represents 1500psi.

Under WOT, fp_h values of 10-14 (1500-2100psi) are typical. Anything under 7 at WOT indicates a potential fuel delivery problem. The fail-safe on the JB4 is set to 700psi and will bump you into Map 4 if values drop below 700psi at WOT. As an additional note, when the N54 is not at WOT the value typically remains at 5 (750psi).

IGN_1 & IGN_2-6

Ignition advance measured in each individual cylinder. Ign_2-6 are further right on the .csv file, however, they all represent the same thing – ignition advance. Ignition advance refers to crank degrees before top dead center (BTDC) when the spark is generated to ignite the air/fuel mix in the cylinder. The air/fuel mixture is actually ignited during the compression stoke before the power stroke begins. Ignition advance, or ignition timing, simply indicates exactly when the mixture is ignited. Advancing timing means the mixture ignites further from top dead center; retarding timing means the mixture ignites closer to TDC.

Too Much Ignition Advance

Timing is one of the most important factors in tuning. Too much ignition advance may cause the air/fuel mix to reach a complete burn before the piston begins the power stroke. You now have powerful gases trying to push the piston downwards while the piston is still traveling upwards. Too much timing increases the risk of knock and pre-detonation, which is a recipe for blown motors. This is not to scare anyone and it should be noted the N54’s knock sensors are very sensitive and the DME is incredibly good at reacting and pulling (retarding) timing when the slightest knock is detected.

Too Little Ignition Advance

Ignite the air/fuel mixture too late and you are leaving power on the table. When the mix ignites too late, the piston is already moving downwards before the cylinder reaches a complete burn. Therefore, there is less force pushing the piston down thereby generating less power and torque.

N54 Ignition Advance – What to Look For

As stated above, the N54 has sensitive knock sensors and the DME reacts quickly. However, all N54’s will encounter knocking and timing corrections from time to time. Here is what to look out for with ignition timing:

  • Timing corrections of 3° or more
  • Consistently poor timing on one or two specific cylinders

Timing corrects of 3° or more typically indicate potential knocking activity. Although, even bone stock N54’s will see timing corrections. Don’t panic if you see timing pulls on various cylinders from time to time. However, if the timing corrections are consistently occurring that may indicate your tune/boost targets are too aggressive for your fueling. Additionally, consistently poor timing or timing pulls on a specific cylinder may indicate an issue. Common causes of poor timing and/or timing pulls include:

  • Tune too aggressive for fueling
  • Spark plugs
  • Ignition coils
  • Leaking injector(s)
  • Dirty intake valves in need of cleaning/walnut blast

N54 Ignition Timing Curve

The graph below shows an N54 running a modest tune with peak boost around 11psi on 25% E85.

*Pull ends at 5500rpms. Timing should continue to increase in the upper RPM’s

Ignition Timing Curve

This is pretty strong ignition timing for the N54 and do not expect to see this on more aggressive tunes with pump gas or low E85 mixes. The overall curve should look relatively similar with more of an up-slope on the right side (assuming you pull to redline or close). Timing typically starts high and slowly drops a few degrees in the mid-range, where it reaches its lowest point around 4,700-5,300 RPM’s, before increasing on the top end. This is not exact science and it will vary from N54 to N54, tune to tune, etc.

Lastly, cylinder 1 is in purple while cylinders 2-6 appear orange and track perfectly. Cylinders will not always track perfectly – it just so happened 2-6 did. It is not concerning that cylinder 1 is off by a bit as it is within a reasonable range of the other cylinders. Additionally, there are no timing drops over 3 degrees. To re-iterate, the above graph shows aggressive ignition timing and is not always “normal”. More on this in the very next parameter.

Aggressive Tunes & Ignition Timing

The next JB4 interface graph shows a much more aggressive tune on an N54 running only 25% E85/91 octane.

Poor Ignition Timing

This tune is too aggressive for the fueling. Timing falls flat on its face as boost nears target. Though, as boost tapers off throughout the mid-range and top-end, timing also begins climbing. Notice cylinder 4 experiences a timing drop of roughly 4° in the mid-range. This is likely the DME picking up potential knock activity and quickly pulling timing. Following the timing pull, cylinder 4 slowly works its way back up.

Additionally, you will notice the timing pull on the 3rd to 4th shift. It is normal for timing to drop to 0° during the gear change. Cylinders 2-6 immediately recover, however cylinder 1 remains at 0° timing. It’s tough to see but you can see a small bump where cylinder 1 tries to recover, but immediately pulls back to 0. This is referred to as flat-line timing. Unfortunately, based on our knowledge, there is no one solution to solve the flat-line timing issue. This particular N54 is very well maintained; spark plugs and coils are new, injectors are index 11+, the engine was recently walnut blasted, and cylinder compression checks out. The flat-line timing in this case is likely tune related, and may require custom tuning to correct.


AVG_IGN represents the average timing below the absolute maximum possible curve during a short period. Lower numbers indicate more aggressive timing. A value of 0 indicates the N54 is running the most aggressive timing allowed by the tune. Average ignition of 6 means the engine is running 6° under the maximum timing allowed. A modest tune with high E85 mixtures will typically result in values around 1. An aggressive tune with pump gas will usually result in values over 5.

This is an important variable for JB4 map 3 and map 5. Values below 1.5 result in map 3/5 targeting maximum boost allowed on each map. Anything over 1.5 results in lower and lower boost targets as average ignition increases. Lets tie this back into what we discussed about ignition timing above.

First timing example = 0.8 AVG IGN

Second timing example = 3.0 AVG IGN

Though both logs were done with the same 25% E85 mixture, the first log only targeted 11psi while the second log was target 17psi and overboosting to 18+psi. The modest 11psi tune resulted in an average ignition of 0.8, indicating aggressive timing. Higher boost resulted in higher average ignition. The N54 was basically retarding ignition timing 3° below the maximum since the tune is on the aggressive end for the low E85 mix.


Calculated engine torque from 0-100 lb/ft. Don’t panic – this is not your actual torque, but rather the torque the DME thinks it’s making. Back-end flash tunes on the JB4 communicate higher than actual torque to the DME. This ensures transmission line pressures are maxing out. Relatively unimportant N54 parameter, so we will leave it at that.

Trims/Trims 2

Short-term fuel trims calculated from 0-50 for bank 1 and bank 2, respectively. 0 = -33% trims. 25 = 0% trims. 50 = +33% trims.

Fuel trims are essentially the adjustment the DME is making to fuel flow and fuel mixture to maintain balanced AFR’s. This parameter may vary a decent bit, which is normal. However, if trims stay pinned in the upper 40’s or 50 then pay attention to AFR’s. Maxed fuel trims often cause the N54 to run lean – not good. The trims parameter is also used to calculate another JB4 parameter – FOL (fuel open loop). More on this later, but high trims will cause FOL to trend up.

If trims are high along with lean AFR’s:

  • Tuning changes may be needed
  • Check codes; O2 sensor issues may cause lean AFR’s and trims pinned to 50

Below we see an N54 running about 40% E85 on the MHD pump back-end flash (pump flash only intended for 30% E85 max):

N54 Fuel Trims

As boost kicks in you can see AFR’s running on the lean side. Trims max at 50 briefly in order to bring AFR’s back on track. The high and low pressure fuel pumps are keeping up with the requested fuel flow. As such, the high fuel trims are likely a result of an E85 mix too aggressive for the given tune.


DME BT shows the DME/ECU’s boost set point. The parameter is determined by the DME and flash tune (if you are running a JB4 back-end flash). DME BT only affects the JB4’s boost target if it drops significantly, usually due to traction control events or limp mode. Otherwise, this is generally an unimportant parameter for reviewing logs.


Represents methanol injection flow from 0-100%. If you’re not running meth you should not be using map 3 on the JB4 and you can disregard this parameter completely. We won’t go into this parameter any further as we recommend doing some extensive research prior to running meth. Meth injection is a suitable option for those who do not have easy access to E85. However, we prefer to run E85 and recommend others do the same rather than relying on meth injection for octane and knock prevention.


This parameter displays the fuel pressure supplied from the LPFP (low pressure fuel pump). Normal values are about 55-70psi. Values below 50 typically indicate an issue with the LPFP, or your E85 mix is too aggressive for the pump. The stock LPFP can generally handle about 30-40% E85 on a bolt-on N54 with stock turbos. Though, with the age of N54’s on the road today there is a chance the pump is exhausted and cannot handle that much E85. If your LPFP is showing its age and you plan on running E85 mixes consider upgrading to a stage 2 LPFP. We recommend Fuel It.

The below N54 datazap log shows a healthy stock LPFP running ~40% E85.

N54 LPFP Fuel Pressure

As shown by the pink line up top, this OEM N54 LPFP remains in the ballpark of 60-70 throughout the entire pull. Despite the 113k miles on this pump and demanding fuel flow from the upgraded inlets/outlets the LPFP manages to hold up even on 40% E85.


Air-Fuel ratios for bank 1 and bank 2, respectively. Under lower engine loads AFR’s are typically around 14.5-15:1. AFR’s of 20:1 are typical when coasting/off the throttle. Under WOT on pump gas, AFR’s commonly sit around 13.5-14:1 at peak torque and 12.5-13:1 at peak horsepower. These air-fuel ratios may seem lean to those coming from non-direct injected engines. However, higher (leaner) AFR’s are normal on direct injected engines like the N54.

**The N54 O2 sensors read lambda NOT actual AFR’s. Therefore, E85 mixtures will not read richer AFR’s even though actual AFR’s are richer on E85. For example, if you are running 100% E85 at a 0.90 lambda then you will see AFR’s of 13.2:1 (14.7 x .9 = 13.23). However, the stoich for straight E85 is 9.765 so your actual AFR is 8.8 (9.765 x .9 = 8.7885). This could be a post of its own, but we will leave it at that for now.

N54 Lean AFR Causes:

  • Faulty O2 Sensor(s)
  • Faulty fuel injector(s)
  • Maxed fuel trims
  • Old/worn fuel pumps or too much E85

This is by no means an exhaustive list of issues that may cause lean AFR’s, but they are some of the more frequent causes.

The below log shows healthy AFR’s on the N54 with 30% E85:

N54 AFRs

Air-fuel ratios start right in the ballpark of 15:1 at lower engine loads as the turbos build boost. Soon after boost reaches target, AFR’s dip down to roughly 13:1 and hold there throughout peak-torque. Peak power on this N54 should occur in the low 5000rpms where we see AFR’s in the ballpark of 12:1 where they remain for the rest of the log.


The gear your N54 is in from 1st through 6th gear.


*You’ll notice FF also appears at the top of the JB4 log spreadsheet. The two values are different. We’ll touch on the one up-top later and is the more important FF.

FF stands for feed forward. FF on the spreadsheet (just right of gear) represents the FF curve. This is the base WGDC before the PID output is added. The FF curve is a function of boost target, RPM’s, pedal input, and other various undisclosed data. This FF can be ignored for the most part; we will revisit the other FF later.


Load displays the DME’s load index. With JB4 only you usually do not need to pay attention to load. However, it is an important parameter when working on back-end flash tunes to identify where tuning changes may be required.


Ignore – this is an internal JB4 value and has no meaning to anyone other than BMS.


The current JB4 map your N54 is running.


Engine oil temperature. Ideally, once fully warmed up, oil temperatures should remain in the 210-240°F ballpark, however it is not uncommon for oil temps to reach 250+° – especially on N54’s without a factory or aftermarket oil cooler. Our N54 335i is equipped with a factory oil cooler and during Colorado winters temps rarely exceed 240. However, aggressive driving during the summer causes temps to reach 250-255. Limp mode will engage if oil temps exceed ~275°. We recommend allowing the N54 time to cool down when temps exceed 260°F.

*We strongly advise against pushing your N54 prior to oil temps reach at least 160°F. If you’re going to push the N54 extremely hard (i.e multiple gear high speed pulls, aggressive cornering, or tracking) consider allowing oils temps to reach 180°+.


Engine coolant temperature. Once fully warm, coolant should remain in the 200-220°F ballpark. Temps may exceed 220° on hot days when pushing the N54 hard. Per BMW, ideal coolant temps are 212-221°F to keep friction as low as possible.


Transmission fluid temperature. The typical range on a warmed up transmission may vary from 175-240°F. Highway driving usually results in temps on the lower end. City driving, aggressive driving, tracking, etc may result in temps reaching upwards of 240°F. Per ZF, the transmission will not throw codes for overheating until nearly 265°F. Although, we recommend allowing a cool down period if temps exceed 240.


This parameter displays your N54’s E85 mixture from 0-170 (divide by 2 for ethanol content. E40 fuel would show as 80). If you are using a flex fuel sensor then the JB4 parameter will show the exact ethanol content as read by the sensor. For those of us who have not installed a flex fuel sensor, the E85 reading is virtual. It essentially uses the various parameters and data to back into the E85 mix. It is typically within a +/- 5% range.


Actual vehicle speed in miles per hour.

Other JB4 Values/Parameters (At Top of Spreadsheet)

*Left to right, top to bottom


Current JB4 firmware version


JB4 interface used for log (Android, iOS, etc)


Your engine. Ex: “E Series – N54”


TMAP voltage


Same as discussed above. The average ignition displayed at the top of the spreadsheet is simply the average ignition the moment the data log ends.

DWP – Default Wastegate Position

Waste-gate position when off the throttle. This is a user adjustable value with a default setting of 60. Can be used to minimize off throttle waste-gate rattle. Lowering the setting may help reduce rattle, but the waste-gate will remain more open when getting back on the throttle. This may cause a bit of extra turbo lag.


Only relevant when running meth injection.


As discussed above, FF is short for “Feed Forward”. The FF displayed up top is a user adjustable variable that also adjusts itself over time as part of JB4 learning. It is the starting point for boost control and PID adjusts WGDC above or below the FF value for more accurate tuning. This value should be left alone for the most part as it learns and adjusts on its own.

MethSafeMode, MethAdd, Methscale, MethPSI 

Only relevant for meth injection.


Your BMW’s VIN. May just show ….. if no VIN is input.


User defined value found on the WMI (water-methanol injection) tab. Should read “NONE” unless running flex fuel or meth injection sensors.


Virtual sensor offset as found on WMI tab. This value has a default of 132 on E85 back-end flash maps or 142 on pump gas maps. This value helps the JB4 determine the virtual E85 reading.


Fuel bias for each 500rpms starting at 3000 and ending at 7000. Typically used on map 6 for troubleshooting. The values should all read 0 unless you are experienced/knowledgeable adjusting these parameters and/or instructed to do so by an experienced tuner.


User adjustable boost safety value. Default value of 18psi. JB4 will default to the safety map, map 4, if boost exceeds 18psi. If you are running an aggressive back-end flash you can bump this value up. Remember, boosting over 20psi requires an upgraded TMAP sensor. We also do not recommend pushing stock turbos past 18psi unless on upgraded inlets/outlets.

PID Gain

Represents how far away from the FF curve WGDC is allowed to stray. User adjustable value of 25 on the N54. Do not adjust unless experienced or directed to do so.


Automatic shift boost reduction for AT cars. On auto transmission N54’s you may experience a boost spike upon up-shifts at WOT. If the boost-spike causes boost to shoot too far over target you may experience timing pulls, throttle closures, etc. This user defined variable has a default value of 60 and may be adjusted to correct drastic boost spikes on up-shifts. This is a part of the PID tuning parameter, and is best left untouched. Post on the forums for advice on how to adjust parameters if you are experiencing issues.


Short for fuel open loop. This is a user adjustable value that also adjusts over time as the JB4 learns. Fuel open loop is a bias applied to the HPFP – higher Fuel_OL values cause the DME to see lower HPFP fuel flow. As such, the DME will increase fuel flow. This value adjusts itself based on the trims signal discussed above. If fuel trims are high then Fuel_OL will trend upwards. If trims are below 25 then Fuel_OL will trend down.

The default value is 70 and the maximum value is 100, however it will only auto adjust up to 90. If you are still having issues you can adjust Fuel_OL to 100, however this is not necessarily recommended. You are better off narrowing down the actual issue. A few common causes of Fuel_OL pinned at 90 include:

  • Weak LPFP and/or HPFP
  • Too much E85 for stock fueling
  • O2 sensor faults

1st_limiter, 2nd_limiter, 3rd_limiter

Boost limits by gear. Values of 0 disable this feature (no boost limit set). Our 335i is RWD running 17×7.5″ snow tires during the winter. Traction is a major issue in 1st gear, so during winter time we limit 1st gear boost to 12psi. If you’re having issues with traction in 2nd gear this feature may be used for the same reason.

3rd gear boost limits may also be used if you’re having traction problems in 3rd. However, 3rd gear boost limits actually come in handy for diagnosing issues. For example, let’s say you’re having issues with consistent/frequent timing drops on logs running 15+psi. You could try setting a 3rd gear boost limit of 10psi, for example. If the timing issues resolve then you 15+psi is likely too aggressive for your fueling. If timing issues still occur on lower boost, then you have have a hardware issue such as old/faulty spark plug(s), coil(s), fuel injector(s), etc.

FUD – Future Use D

This could be a post of it’s own. For most of us, there is no need to use the FUD feature. You can essentially opt to change/disable some JB4 features with this. For example, bit0 (FUD 1) disables JB4 steering wheel controls. Bit2 (FUD 100) can be used to replace oil temperature warm-up safety with water temp. In layman’s terms, the JB4 defaults to using stock boost until oil temps reach 160°F. This FUD option would change the oil temp default to using coolant temps.


Displays 0 if you are on stock TMAP sensor. If you install a 3.5 or 4bar TMAP sensor you must adjust this value accordingly.


As discussed initially in this post, this is the value input to enable 6 cylinder logging. If your DME is I8A0S you should have input 4 in the user adjustable settings, or 5 for IJE0S. The value you entered should show up on the log under 6CylMode.


When the JB4 detects an issue it will bounce you into map 4. The LastSafety simply shows the reason your N54 was last bounced into the safety map. This value will range from 1-5, and references the following safeties:

  1. Boost Over Safety
  2. AFR too Lean
  3. Fuel Pressure Low
  4. Meth Flow Low
  5. Fuel Trim Variance

If you are frequently bounced into the safety map you should pay attention to the reason. That will help you determine where to being with diagnostics to correct the issue.


Similar to fuel_30-70, this is a duty bias applied each 500rpms from 1500-7000. Typically used in conjunction with map 6 for troubleshooting purposes. These values should read 0 unless you are experienced altering these values, or receive direction from an experienced tuner.

Summary on JB4 Data-Logging

**We will expand on this post in the near future with additional examples of data logs and what to pay attention to.

Data logging is an important and useful feature for those looking to push their N54 while ensuring the engine is running well. The N54 is an extremely tolerant engine. As such, even when AFR’s run dangerously lean or timing drops occur all over the place the N54 usually keeps chugging along without any serious consequences. However, constant abuse over years may cause premature wear on your N54. You definitely do not want the engine to be leaning out consistently.

This is where data-logging comes into play. It is always a great idea to get a few data-logs from time to time and take a look at all of the parameters. If you are not comfortable reviewing logs on your own, feel free to e-mail them to us or post on the forums. Additionally, any time you make tuning changes or additional mods it is a good idea to data-log. The more power, torque, and boost you are making the more important data-logging becomes. Running lean on 10psi likely will not cause any harm; running lean on 20+psi may be a different story. Have some fun data-logging your N54 and please be safe. We will expand upon this post in the future, but feel free to reach out with any questions in the meantime.

Check out our post about building a 500hp N54 for under $1,500

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  1. CALC_TORQUE – It cannot only be from 0 to 100 lb/ft. Surely it must be from 0 to 1000lb/ft. The value is typically low value double digits in the logs. It would be close to accurate if multiplied by 10.

  2. Current JB4 firmware for N54 data log does not any longer provide E85 %. BMS has collaborated with Fuel-it forcing us to purchase Fuel-it’s ethanol kit (at a substantial price) in order to obtain E85% info. I’m not happy about this.

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