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Wideband EFI Tuning
courtesy of Innovate Motorsports & author Standford Curry

NOTE:  While the article is a bit dated and uses the older LM-1 Air/Fuel Meter, the principles of EFI tuning and the steps described are just as relevant when using the newer (and easier) LM-2 Air/Fuel meter & Sensor Device.  Keep the article and study the methodology demonstrated.

Whether a fuel-metering device is physical (carburetion) or electronic fuel injection (EFI), manufacturers tend to apply a “lowest common denominator” approach to their generic “out-of-the-box” tune. This helps them get customers up and running quickly (but not exceptionally well) for the majority of applications. The systems are tuned to operate in a wide range of engine combinations, climates and fuel formulations. However, optimal performance doesn’t come from an out-of-the box, generic setup

Innovate’s wideband tuning tools (LM-2, LM-1/LMA-3 or LC-1/DL-32 are three examples) allow you to optimize performance from an EFI system. The Innovate Motorsport system captures information about how your car runs at wide-open-throttle, cruise, idle and transition – helping you optimize your engine’s tune and improve your car’s performance. Innovate Motorsport’s products log everything from basic RPM and Air/Fuel Ratio and Manifold Absolute Pressure (MAP) to more specialized parameters like Throttle Position and Intake Air Temperatures . After recording the data with the Innovate system, you can analyze this data, adjust a few calibrations in your EFI system’s “fuel map” and then run the car again to check your results for performance gains. Less time spent guessing your way through fuel maps gives you more time for the track and a better chance at the trophies. (Installation Tips).

Most EFI systems – including the aftermarket “piggyback” or “black box” systems that operate on top of factory Engine Control Units (ECUs) – rely on a basic fuel map for metering fuel. The fuel map is either pre-installed or it requires the user to pull a fuel map calibration down from the EFI system manufacturer’s Web site using their laptop and then upload the fuel map calibration to the EFI system’s Engine Control Unit (ECU) or associated piggyback system. An EFI system’s fuel map can be thought of as a three-dimensional (3D) map of X (Engine RPM), Y ( Load / Throttle Position ) and Z (Fuel Amount to Inject). A similar 3D map applies for spark advance by replacing axis Z’s “Fuel Amount to Inject” with “Degrees of Spark Advance.”

Example 3D EFI Map

The nice thing about using Innovate’s LM-1 or LM-2 with the LMA-3 to tune an EFI setup is the selection of sensors which feed the EFI system. Wires for the Throttle Position Sensor ( TPS ), RPM, Manifold Absolute Pressure ( MAP ), Intake Air Temp (IAT), Coolant Temp and Crankshaft Angle are used by EFI systems to calculate the proper time and amount of fuel to inject while the engine is running. This “pre-wiring” makes it convenient to attach the LMA-3 wires for channel input onto the wires that go into the EFI system’s brain, giving you access to a wealth of data. The sensors for RPM, MAP , and TPS were tapped for the purposes of this discussion.

1 Recording & Displaying Live Data: With your LM-1 (or LM-2) and LMA-3 installed and tapped into the relevant sensors, it’s time to take your car for a drive, capture some data and interpret the results. Capturing data is as easy as hitting the “Record” button once to start recording (“R” will flash on the LM-1’s display) and once again to stop recording. Each recording is referred to as a “Session.” You can record multiple sessions and up to 44 minutes of total recording time before you need to download the data to your laptop and free up the LM-1’s onboard memory for additional recording. Using a laptop attached to the LM-1, you can also maximize the LogWorks Monitor display to see your car’s Air/Fuel Ratio , RPM, Manifold Absolute Pressure ( MAP ), Throttle Position and Acceleration while the car is running – very helpful while you’re tuning the idle in the garage or riding as a passenger while someone else drives the car.

LogWorks Virtual Gauges Showing Air/Fuel Ratio, TPS, MAP, Acceleration, etc.

2 Downloading & Viewing Recorded Data: Innovate makes it easy to pull recorded data down from the LM-1 to your laptop. With your laptop connected to the LM-1, open up the LogWorks Monitor software and click on the “File” drop-down menu, then highlight “Download LM-1 Log” to load your recorded data to your laptop. Once the download completes, you’ll see a new window appear with a graphical representation of your session, similar to the screen shot below. You can toggle between multiple sessions using the “Session” drop-down menu of that new chart.

Screen Capture of new LogWorks session chart- Air/Fuel, RPM, MAP, Accel 1.jpg

It’s a good habit to immediately save this newly downloaded data onto your laptop before you clear out the LM-1’s memory storage of its old sessions. First click on “File” in that newly created graph’s window, and then click on “Save As.” Type a filename that includes something memorable about the session. An example is “1ClickLessFuel2000_2500RPM_AllMAPs.log” to denote taking one unit of fuel out from 2K-2.5K at all load levels. This practice helps you make sense of the log when you revisit it 3 months later. You can then clear out the LM-1’s memory by going back to the LogWorks Monitor and clicking “File” and then “Reset LM-1 Log.”

3 Baseline Practices: One of the first things tuners do before altering a fuel curve on any EFI car is to make a copy of the existing EFI system’s map – assuming that the system allows you to copy the file to your laptop and later upload that file back into the ECU. This is helpful when you want to undo a change you’ve made to the fuel map. Now is also a good time to capture some baseline data about how the car runs before you make any adjustments to the original fuel map. Drive the car, record the data and download the data (and ECU fuel map file if possible) to your laptop – before making any changes. Then analyze the data, make your adjustments and drive the car again to determine if your changes resulted in the desired effect.

A good, safe practice is to baseline (and data log) a few runs on the dyno before making any changes to the fuel map (or spark map for that matter). With your baseline captured, you can compare your baseline run data against subsequent run data (done after adjustments).

4 Idle Tuning: Compared to the effort required to tune a carbureted car’s idle circuit (which does double duty as the cruise circuit), tuning EFI systems for idle & cruise with a wideband is very simple. Most EFI systems apply the axes of RPM and Load ( MAP value) in order to arrive at an amount of fuel to inject. In the following diagram of an EFI system’s fuel map, Engine RPM is the horizontal X axis and Load (MAP value) is the vertical Y axis. The numbers in each X-Y cell tell the EFI system how long to hold a fuel injector open for that RPM and MAP value.

EFI Fuel Mapping

For an example, say that you’ve captured some data and are reviewing it in the LogWorks interface shown in the following diagram. You click on LogWorks’s gauge-like button in the upper left hand corner of the window, just below the drop-down menu for “Channels” to allow you to add a metrics box that shows the values of the data collected at that point in time. You can add as many metrics boxes as you like, and you can remove them just as easily by clicking on them again. The graph shows that at a 900 RPM idle the Air/Fuel Ratio is 13.5:1.

Idle Tune Air/Fuel Graph

If you want to lean it out just a tad (EFI guys are such perfectionists..) just open your EFI system’s interface and make a few changes. With the interface open, locate the 900 RPM range for -12 to -10 PSI of MAP or Vacuum , highlight those cells as shown in the following diagram and then tap the minus key (-) to reduce the amount of fuel administered to your engine at idle. Less sophisticated EFI systems may require you to manually type in the values for these numbers, but even typing still beats the carbureted alternative if twisting mixture screws and replacing idle air bleeds.

Idle Change in ECU Software

Start the car up again and check the LogWorks gauges. The Air/Fuel Ratio has changed to 14.6:1 and the idle is now smoother at 860 RPM with about the same Vacuum . Some EFI interfaces even allow you to make your fuel mapping changes with the engine running, so you have the option of adjusting the fuel map while looking at the LM-1’s Air/Fuel Ratio display.

EFI LogWorks Virtual Gauge Dials

Note: Most EFI systems will have a menu option that allows you to trigger an idle compensation system when the car’s automatic transmission is in Drive but the car standing still. For those systems that don’t, the previous tuning process can be used for cars with an automatic transmission. Remember to chock the wheels, engage the emergency brake and have a friend in the driver’s seat pressing the brakes as you tune with the transmission in Drive. You can then sit in the passenger’s seat to make the fuel map adjustments using the laptop.

5 Light Cruise Tuning: Next, you can measure and tweak (where necessary) the values in the EFI interface to the right of the cells you just changed. That section (1500 RPM and up, -11 to -12 PSI load ) is used for very light cruise conditions with very little load . Capture your data, make your changes to no more than two horizontal rows at a time, drive the car, capture more data, analyze and repeat as necessary until you feel like your cruise Air/Fuel Ratios are in the range you want them in and you haven’t sacrificed drivability or safety. Again, look at your knock voltage readings and compare these against the baseline for any discrepancies. This process allows you to analyze whether your changes resulted in the Air/Fuel Ratios and drivability you sought in that range.

Save the Innovate data captured from the LM-1 (and the EFI system’s current file if it allows you to -- using a similar filename convention) under a filename that makes sense to you for the changes you’ve done. You can at this point begin working your way upward 1 or 2 rows at a time on the EFI system’s map to build out the cruise and transition section of the map. That process is described along with a couple of options for tuning the transition section near the end of this discussion.

6 Wide-Open-Throttle (WOT) Tuning: The same level of simplicity applies for tuning the car at wide-open throttle – it’s just a different area of the map. Ideally, WOT tuning should be done at a dyno (to measure wheel horsepower and torque) and then the racetrack (compare quarter-mile ET and MPH as well as 60 foot times off the line). Tuning for WOT focuses on the upper part of the EFI system’s fuel map shown earlier, where vacuum is closer to -1 or 0 (or positive values for boosted applications) and extends all the way from idle RPM through redline.

Most manufacturers will tune the EFI system to run between 11.5:1 and 12.7:1 in the high load , mid-upper RPM range for optimum power and engine reliability, while running mixtures near 13:1 at slightly lighter loads (-2 PSI). For even lighter loads, the EFI system switches into a “closed loop” feedback system that targets 14.7:1 for optimum fuel economy and emissions.

Looking at the high-load part of the map in the following table, look at the turquoise rows of Air/Fuel Ratio . This map is a LogWorks table taken from a Honda S2000 running on its factory fuel map. The table consists of many sessions collected across a wide range of throttle, RPM and load conditions.

Baseline Table

At the 0 and -1 PSI range (Wide Open Throttle), the Air/Fuel Ratio is between 11.8:1 and 12:1 from 1500 RPM up to 8250 RPM. However, the Air/Fuel Ratio seems to drop after 8250 RPM down into the 10:1 range – not conducive to maximum power. This is where Innovate’s data logging can find you some horsepower by highlighting an opportunity to raise the Air/Fuel Ratio back into the 11s from 8250 to redline. The pink Air/Fuel Ratio line in the corresponding dyno run from this Honda confirms that the engine goes too rich after 8250 – the pink Air/Fuel Ratio line drops over a full point of Air/Fuel Ratio from 7500 RPM to 8500 RPM.

Baseline AFR Example

What’s happening is that Honda deliberately adds extra fuel after 8400 RPM (the stock S2000’s power peak) to drop the Air/Fuel Ratio down into the 10s. This artificially limits the power peak to 8400 RPM instead of the engine’s true peak flow potential at 8800 RPM – where 8-12 more horsepower is available. Honda does this to reduce the likelihood of an average owner bumping into the fuel cutoff at 8900 RPM. Aftermarket “black boxes” like those from Greddy and Apex can run on top of the factory ECU, allowing an experienced tuner to use a wideband system like Innovate’s LM-1 and tap that extra 12 horsepower by trimming the excess fuel injected between 8400 RPM and redline. This can be done by plugging your laptop into the black box’s interface and editing the relevant RPM/ Load cells in a fuel map screen that’s similar to what was described earlier in the Idle section. If you instead have a “stand-alone” aftermarket ECU in place of the factory ECU (as in the following diagram), you simply open up the interface and make your changes to the RPM/ Load cells there, and then go back and test for the resulting changes.

WOT Fuel Trim

It’s safest to do this type of fine-tuning on a dyno first, paying careful attention to the Innovate LM-1’s Air/Fuel Ratio readout and data logs in the areas of RPM and Load where you made the changes. In addition, pay close attention to the knock voltage you’re logging in the LMA-3 and viewing in LogWorks. Compare your baseline logs against each set of changes so you can avoid harmful detonation.

7 Transition Tuning: You’ve now used your Innovate LM-1, LMA-3 and LogWorks software to check for knock and to fine-tune the idle and wide-open-throttle ranges of your car’s EFI fuel map. All that’s left is to “fill in the blanks” between idle and wide-open-throttle in the EFI system’s fuel map. One of the easiest ways to measure and refine your EFI fuel maps in this “transition” area is to take your car to a dyno shop and make many dyno pulls, being sure to capture the data with your Innovate equipment. Although you may need to rent a few hours to thoroughly tackle all the ranges, a couple of hundred dollars is far less expensive than replacing an engine.

Concentrate on one load range at a time and use the Innovate LogWorks Instrument Panel of configurable dials to make each pull. Remember to hit “Record” on the LM-1 before you start this process. One approach is to base your pulls on TPS , making a full pull (from 1500 RPM or so up to redline or until the RPM plateaus) using only 10% throttle. You will have to actively watch the TPS dial and control your foot to ensure you keep it at 10% for the full pull. Then make another pull, this time at 20%, then 30% and so on until you make your last pull at 100% throttle.

Next, you can try capturing data based on making pulls referenced by engine load – trying to keep engine load ( MAP value or Vacuum ) as constant as possible through the pull or until the engine plateaus at an RPM level, starting at a load level that is a row or two above the idle load level you’ve set in the EFI system’s fuel map. This practice is infrequently done, but can provide insight into stumbles or hiccups that aren’t otherwise only show up in normal street driving.

After your final pull (of TPS and Load/MAP), download the data you recorded from the LM-1 to your laptop. Open up LogWorks’s “View” drop-down menu, then click on “New Chart” option to bring up the Chart Settings box like the following graphic:

Viewing New Chart

Set your Horizontal axis to RPM and your Vertical axis to MAP and your Chart Content as LM1_O2 and click OK to bring up the table. Next, click on “Sessions” to select all of your sessions as content for the table you’re building – this allows you to capture all the Air/Fuel Ratio s for the various dyno pulls you just ran and display them as a single table which you can very easily color code for easier viewing.

Enable color-coding by clicking on “Colors” and selecting the color scheme of your preference. Cells in the table automatically become color coded based on their numerical value. The color scheme in the following diagram is “Wobniar” (which is “Rainbow” spelled backwards) and intuitively has blue at the rich / cool side of the Air/Fuel Ratio spectrum and red as the lean / hot side.

EFI Transitions Viewed as Color-coded Table

Review the LogWorks table to examine cells that contain Air/Fuel Ratio s that don’t make sense for the area of the fuel map that they are in. The previous table has a red cell in the lower right corner with a dangerously lean 22.39 Air/Fuel Ratio at 8500 RPM and 8.3 pounds of boost (this table is from an EFI car with a small turbo). The EFI system’s fuel map needs to be checked and likely richened in that range. It also appears that there are some lean cells (over 15:1 Air/Fuel Ratio ) within the 4500 RPM – 5000 RPM range between -12 PSI and -3.18 PSI which need to have fuel added as well.

Remember to make one change at a time, measure the results, and repeat. Soon you will be "finding" horsepower and efficiency in all sorts of unexpected places!

Standford Curry owns and tunes a '69 Chevy Camaro, an '02 Honda S2000, and a '97 BMW M3. He has won numerous SCCA and Club events, as well as placing first in the 1997 North California Solo II complete series.

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