Flying Blind Part II: What To Data Log When Tuning A Vehicle

In our first article, Flying Blind: What To Data Log When Tuning A Vehicle, we took a look at some of the basic parameters to look at when tuning a vehicle with EFI Live. This article will expand on this subject matter as we take a look at different operating parameters and tables with the FlashScan V3. So, let’s dive in.

The keys to using logged data successfully to develop an optimal tune file are understanding the operating parameters of various sensors and relating data to actual working conditions. 

EFILive’s FlashScan and Autocal systems provide “black box” and pass-through data logging capabilities. “Black Box” logging is done directly to the hand-held device and does not require a laptop computer to be connected. As the name implies, pass-through data logging passes data through the hand-held device to a laptop. FlashScan and Autocal devices can also be used to read and reset trouble codes.

Typical GM control systems rely on narrowband oxygen sensors (O2) to control fuel flow during idle and part throttle operations. Consequently, data logs should show that the system was in a closed-loop state, which means O2 feedback to the ECM is used to control fuel flow. If the system is in an open loop, the engine hasn’t reached normal operating temperature, the throttle has been depressed far enough to cause a transition out of closed-loop, or a mechanical or electrical problem is preventing the system from activating closed-loop operation. More than one tuner has chased an air/fuel management problem only to eventually learn that the cause was the system not being in a closed-loop.

Closed-loop operation intends to control idle and part throttle air/fuel ratio so that a stoichiometric ratio (+/-14.7:1 with pure gasoline and +/- 14.1 with E10, gasoline containing 10% ethanol) is maintained. Back in the day, before inexpensive wideband O2 sensors were available, many tuners used narrowband voltage readings to adjust wide-open-throttle air/fuel ratios. Those readings may get you close but are not reliable enough to achieve the desired result.

A wideband O2 sensor is required for accurate wide-open throttle air/fuel ratio data. The output of most wideband systems can be fed into a Flashscan system so data can be displayed on Flashscan’s dashboard. This greatly simplifies tuning because actual and commanded air/fuel ratios can be displayed on the same graph.

When logging wide-open throttle data, it’s essential to install a wideband O2 sensor and connect its output to a FlashScan or Autocal. That allows the data to be displayed on the same data log as the other ECM data. Wide-open throttle testing should then be done on a racetrack or chassis dyno with the transmission in fourth gear, or the ratio closest to a 1:1 ratio. The longer, slower rate of acceleration in the upper gears will allow more data to be collected during acceleration runs. Be mindful that public streets and highways aren’t the proper places to be doing wide-open throttle tuning.

If long-term fuel trim (LTFT) readings are out of the desired range, the best way to correct fuel flow will differ depending on the complexion of the out-of-range readings. Assuming you’re not dealing with a “whacked” volumetric efficiency (VE) table or a damaged Mass Air sensor (MAF), if the trims are way off across the board (in the same direction), incorrect injector flow rate (B4001) values may be the culprit. In instances with LTFTs being excessively positive at some points and overly negative at others, the most likely suspects are the VE table (B0101) and the Mass Air Flow calibration table (B5001). (Note: in EFILive tuning software, all tables are numbered for easy reference. The numbers in this article refer to LS1 operating systems.)

Flashscan’s virtual dashboard contains a variety of gauges that can be altered to fit the specific needs of a tuning operation. On this dashboard, indicators for fuel system status have been added. When the indicators turn orange, the system is in open loop status. When the system switches to closed-loop, the indicators turn dark.

Several other tables can affect fuel flow. So if the data in the tables mentioned above appears to be correct, or if extreme changes are required to bring LTFT numbers in line, you should look elsewhere:

  • B3701- Injector Pulse Width Voltage Adjustment
  • B3702- Injection Timing
  • B4002- Injector Voltage Correction
  • B4003- Minimum Injector Pulse Width

Air/fuel ratio and ignition timing are most commonly the areas of prime interest in a quest for improved performance (and fuel economy). But other “challenges” also exist, so it may be necessary to change the selection of gauges displayed on FlashScan’s virtual dashboard. One of the many advantages of this software is the ease with which existing dashboards can be changed and new ones created. 

The Injector flow rate values for stock injectors are typically very accurate. However, when injector size is changed, that’s usually not the case. Although there are a variety of factors controlling injector output, the flow rate table establishes the basis. This table is for a Corvette which does not have a vacuum-referenced pressure regulator. Consequently, adjustments to compensate for manifold pressure are done electronically. In systems with a vacuum-referenced pressure regulator, all values in this table would be the same.

The system is supplied with many default dashboards with gauges configured for either metric or Imperial data. However, it is possible to alter the “language” displayed in individual gauges. For example, suppose you’re most comfortable with temperatures being displayed in Fahrenheit. In that case, those gauges can be reconfigured to display Imperial data while gauges displaying air flow rates “speak metric” (grams per second). 

Notice that the dashboard shown below has been configured as described with temperatures displayed in Fahrenheit and vehicle speed in miles per hour, while air flow and manifold absolute pressure readings are shown in metric units.

Regardless of the flavor of displayed data, it must be consistent with the relevant tables in the tuning program. For example, you don’t want to log temperature in Fahrenheit and correlate data to a table in the tuning program that references Celsius (centigrade back in the day). 

Even if the values in the injector flow rate table match actual injector flow exactly, fuel trims can be excessive if the values in the voltage adjustment table are not accurate. This is a common problem when stock injectors are replaced. Different brands and styles of injectors typically react differently to system voltage. If the actual injector flow rate has been verified on a flow bench, but fuel trims are excessive, the voltage adjustment table should be modified.

In addition to spark and fuel calibrations, the idle quality frequently requires a good bit of tuning work—particularly in vehicles equipped with an automatic transmission. When logging data for use in idle quality tuning, the relevant parameter identifier (PID) is known as Running Air Flow in Gear (RAFIG), which measures the airflow correction performed by the system. If the value in table B4307 is too far off the mark, an excess correction is necessary to provide the airflow required to support the commanded idle speed. The amount of change is shown when RAFIG is displayed on the virtual dashboard.

Running Air Flow in Park/Neutral (RAFPN) is another PID available in FlashScan. Both RAFIG and RAFPN are computed by adding long-term and short-term airflow correction, so those PIDs must also be selected. However, these values don’t have to be displayed when setting up a dashboard for monitoring or data logging idle airflow correction. RAFPN is the relevant PID when an engine is idling and the transmission is either Park or Neutral. 

After a data log has been recorded, the best way to find calibration problems is to review the data in chart mode. The values listed correspond to the cursor position. In this chart, the cursor has been placed at the upper rpm recorded during the test drive. It shows that the knock retard (KR on the chart) had tapered down to 7.6 degrees after peaking as the throttle was opened. If you don’t speak metric, note that most values, such as temperatures and pressures) can be easily changed to “American” units. Many tuners prefer to see temperatures in Fahrenheit and airflow and pressures in grams and kPa and this can be easily accomplished with EFILive’s dashboards and charts.

Two other PIDs of interest are RAFACIG and RAFACPN, which display airflow correction when air conditioning is turned on. These PIDs consider the airflow modification activated to compensate for the additional load put on an engine when engine air conditioning is switched on. Tables B4354 through B4370 relate to air and spark compensation for air conditioning load. Although spark settings have no direct impact on airflow, they can indirectly affect the amount of airflow compensation required to maintain commanded idle speed.

When troubleshooting, it is often advantageous to zoom in on scale size to provide a better definition. To demonstrate this, the chart shown in the previous photo has had the maximum displayed rpm reduced to 2,000 from 8,000. This is helpful when working with idle and part throttle conditions because it makes small changes more obvious.

The need to address idle quality usually arises after a long duration camshaft is installed, especially if the torque converter isn’t “loose” enough to accommodate the increased idle speed necessitated by the cam. When an automatic transmission is in gear, a relatively high idle speed played against a “tight” converter puts the engine under significantly more load than exists at lower speeds. That additional load increases an engine’s demand for air, and consequently, desired idle air flow must be increased, as specified in table B4307. Even with a high stall converter, or a manual transmission, idle airflow usually has to be increased, if for no other reason than to support an uptick in desired idle speed. 

This is an older chart recorded with version 7.5 software (because a deadline was looming). Note the cursor position (red arrow) at the point where 2.4 degrees of knock retard was recorded.

Another special-purpose configuration option the scanning program offers is setting maximum and minimum values for a gauge or chart. Default settings for gauges encompass the entire range of normal operations. However, it may be advantageous to narrow the scope, thereby increasing definition, for specific tasks. For example, when working with issues related to idle, throttle position will remain in the lower end of the range. Minor changes will become much more apparent if the maximum reading is reduced from 100- to 20-percent. Minimum and maximum values are easily changed, so there’s no need to create a unique gauge. However, you may want to do just that and incorporate it into a dashboard that you design for a specific tuning operation.

When monitoring idle airflow, you’ll most likely find a discrepancy between the observed and commanded data due to adjustments initiated by the data in various tables. LS1 PCMs adjust idle airflow to compensate for engine and vehicle conditions changes and can also learn idle airflow correction. These modifiers may cause actual airflow to be higher or lower than the value in table B4307. Consequently, it may require considerable time and effort to bring RAFIG correction to minimum levels. As long as the necessary amount of correction is within limits, proper idle quality can be achieved; the airflow correction (as shown on the RAFIG gauge) deemed acceptable is primarily a matter of personal preference.

This is the high octane timing table for the calibration that was in control when a knock was recorded in the scan program. Note the red arrow pointing to the gray overlay on one of the cells. The value in this cell was controlling spark timing when a knock was recorded. This makes it much easier to home in on the cells that need to be modified to eliminate a problem. The appropriate cell would also be wearing a gray overlay on all other tables that were controlling engine operation at the cursor position.

During the set up of a custom dashboard, you may well find that the gauges incorporated on “Page A” differs from the charts shown on “Page B” and “Page C.” These pages must be set up separately and allow you to view data in a continual graph format. In addition, you may find that you want different PIDs displayed on each page. Fortunately, it’s possible to accomplish that fairly easily. Extensive dashboard setup and PID selection guidelines are provided with the FlashScan software package.

Correlating Logged Data to Cells in a Table

When tuning, one of the challenges is determining the location of the specific data that must be altered to correct a problem or enhance engine operation. The integration of FlashScan’s scanning and tuning programs simplifies this process by highlighting the cells in a specific table corresponding to the operating conditions selected on a graph of logged data. 

Another nice feature of FlashScan software is its mapping capability. This map shows the average spark advance at the various rpm and engine load conditions encountered during the data log session. The red lines correspond to the cursor position in the data chart.

For example, if knock retard is evident, click hold and drag the cursor across the appropriate section of the graph. Then switch to the tuning program (both can be open simultaneously) and open table B5913 (High Octane Spark Table). Again, the cells containing spark advance settings for the operating conditions (rpm and engine load) that existed when knock was detected will be highlighted. 

As noted previously, the parameters for the PIDs displayed on a chart must be in the same units like those used in the relevant tuning table. Separate metric and Imperial PIDs exist for all parameters expressed in either type of unit, so be sure to select the correct one. Most tables have rows and columns within the tuning program, and unit types may be specified for each.

With these two articles under your belt, you should have a much better understanding of what to data log and what tables to use with EFI Live’s FlashScan V3. In our next article, we will take a look at what’s involved with a remote tune, the process, and the tools needed from EFI Live.


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About the author

Dave Emanuel

Dave Emanuel learned about working on cars the old fashioned way- by breaking them, and making them go faster. He has written over 2,500 articles and seven books and currently owns four vehicles, all powered by LS engines.
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