Technical Information Wideband Tuning


The article is written for the staged system (pre S300).

Wideband tuning - Introduction

Why use a wideband? Full throttle tuning only tunes 1/5th to 1/6th of the available map area. Part throttle where you spend most of your driving time and is the most common area for complaints. (poor fuel economy, roughness, stumbling) Very few dynos are capable holding a constant load for part throttle tuning. Dynos do not accurately represent real world conditions like under-hood airflow at speed and RAM air effects. Typically you car will run leaner off the dyno than on by about 3/10ths of a point.

If you are running closed loop and your part throttle fuelling is incorrect, your full throttle fuelling will be affected. (see closed loop). Another good reason to tune part throttle correctly.

Using a wideband in on road conditions will enable more accurate fuel tuning. This does not replace dyno tuning, but augments it.

Hondata has had extensive tuning time with two wideband lambda meters, the PLX and the FJO. Most wideband meters - (the ones that are of any use in tuning here) have a 0-5 volt output proportional to air fuel ratio. That output is fed back into the O2 sensor wiring where ROM Editor or HondaLogger convert it back into a precise air fuel ratio. The stock O2 sensor is very inaccurate for anything other than 14.7:1 air fuel ratio. (image courtesy of FJO)

Note - you must have Stage 4 as datalogging is used.


For instructions to install the PLX wideband, see this application note:

Remove the stock oxygen sensor and install the wideband O2 sensor.

Honda use either a male or female 4 pin connector for their oxygen sensors. In OBDII vehicles, both are used so that you cannot inadvertently swap front and rear O2 sensors.


  • 1 Power and ground cables for the FJO wideband
  • 2 Wideband O2 cable
  • 3 0-5V Output from wideband to stock O2 wiring
  • 4 In car air fuel ratio LED display

You can make an adapter (using the plug off a dead O2 sensor) that connects the 0-5V wideband output to the stock oxygen sensor plug. Tha adapter plug does two things. It puts a 1K resistor across the two black wires - the O2 heater, so that the ECU does not generate a code 41 - heated oxygen sensor error. Even if you do get this error the ECU functions normally.

The other two wires, typically green and white are ground and signal, which are connected to the wideband's ground and signal output.

ROM Editor and HondaLogger Setup

Open settings, click edit conversion table under Lambda and type in the voltage-airfuel values for the wideband you will be using. These values should be found in your wideband's documentation.

Edit Target Lambda and change the 750 Mb column to 12.94 by pressing the J key. This will get you closer to peak power for 750 mb air pressure. Remember that these target values are just suggestions. Your engine may require more or less fuel for maximum power.

Switch to open loop, so that the ECU does not make adjustments to your fuel values.

Set acceleration enrichment to zero - which due to a bug in ROM Editor 2.5 is labeled as cranking enrichment. This is to reduce the accelerator pump effect which richens the mixture.

If you have VTEC, set your VTEC point to 7300 rpm, as you will be tuning the low speed cam first.

Checking operation

Start the car and read the airfuel ratio from the wideband's display. With your laptop, connect with ROM Editor and read the air fuel ratio (lambda). The values should be similar.

If the signal and ground are reversed, the lambda value might read high - say 20, and the car may run badly due the ECU being fed an incorrect negative sensor voltage.

Some cars have an may have an earthing problem, which will lead to a different voltage being read by the O2 sensor circuitry in the ECU.

Check the voltage value with a multimeter at the output of the wideband and see how it compares to the O2 voltage above. If there is a difference, install a diode with the diode cathode pointing to the FJO and the anode pointing to the the O2 plug (green sensor ground wire) The diode is type 1N4001, Radio Shack part # 276-1101. This prevents what is called a ground loop.

Tuning part throttle

Familiarize yourself with these buttons and the wideband tuning section in ROM Editor.

Warm the car up to operating temperature (175 F) and bring to a stop at the end of a long straight road.

Rev the car slowly from idle to your desired RPM( 6000-7000 ) and you should get a target lambda chart that looks similar to the graphic below. This tells you how rich or lean you are running by percentage. Put the car in first gear and drive the car slowly in first (or second). Values in column 4 should start to be recorded as you move to a higher lower vacuum with more load column 5.

Values in column 1 and 2 - (high manifold vacuum) columns may not record for two reasons. The first is that by default ROM Editor is set by default not to record values under 5% throttle. This is because under deceleration the injectors shut off and the wideband meter will read very lean air fuel ratios of 17-20. (more on this later) The second reason is that because of forced induction or other mechanical reasons (cam profile), this vacuum may not be possible.

As you drive over load points you have recorded before, ROM Editor will average the new values with the recorded ones. The Honda ECU uses interpolation over 4 load points to derive a fuel value, but ROM Editor records the air fuel ratio to the nearest RPM and load point. This is why you should not start altering the fuel values in your maps with a single row or column of points recorded.

Now you are ready to start making some changes. Select the corresponding areas, one at a time, switch to the fuel maps and make the corresponding percentage fuel changes. Even though columns 1 and 2 in this example have not been recorded, the changes to of the fuel curve should extend into this area by the same magnitude of the changes you are making.


Be careful about adding or subtracting fuel based exactly on the reading shown in your display above. If you are lean along a specific range of rpms or across a few MAP values, add fuel at least one rpm range before it as it affects reading in that area. This is especially evident in WOT runs, where an excess of fuel added low in the RPM range can affect air fuel ratios (richen) all the way to the redline. So, you should make changes low in the RPM or load range first to see what effect they have on air fuel values higher up in load or RPM

Rewrite the chip or download the changes to the emulator. Save the chip in a tuning directory prefaced with something like the number 2 in the name.

From the Edit menu select Clear Lambda Highlighting - ctrl L. This erases the recorded lambda values. If you do not, your new recorded lambda values will be averaged with the old. Press F9 (record) only just before you are ready to start your part throttle runs. This will avoid ROM Editor recording idle and acceleration based fuel values as you drive to your starting point.

Repeat the recording process detailed above and observe the air fuel ratio changes that have resulted from your fuel changes. Now you can select smaller areas and make finer changes. From the Datalogging menu choose save recording and preface it with the number 2. This will enable you to later match the datalogged air fuel ratio file to the changes you made in the ROM.

Part to full throttle tuning

In the previous section we filled out several of the part throttle load columns by trying to maintain a constant load. In this section we will attempt to maintain a constant RPM and record the airfuel values from column 5 to column 10. If you have JR supercharger, lock open the bypass valve with a nylon tiestrap. At this point we do not want to generate boost. It you have a turbocharger, set the boost value as low as possible - preferably zero.

There are two techniques to part throttle tuning.

  • The first involves depressing the brake while accelerating to maintain a constant RPM, so as to fill in as many load values as possible. We have had reports back that this produces falsely rich values leading to overleaning the fuel tables. (Thanks to Torin Finver for feedback on this)
  • The second technique is to continue with smooth acceleration and WOT runs normally (without using the brake pedal) and to extrapolate the missing numbers. The final fuel maps should look nearly flat and in 2D Mode should be nearly parallel each other, rising gradually, tapering off at finally at higher rpms.

Braking technique

Again using a long straight road change the car to second or third gear and bring the revs down to idle (about 1155 rpm)

Depress the brake while depressing the accelerator. Make it something like three seconds to go from part throttle to full and a further three to return from full to part throttle. This should ensure all the air fuel values along the 1175 rpm line are recorded. This is quite difficult. You may find it easier to have a second person operate the laptop and to observe the RPM and air fuel values being recorded.

Increase the revs to the next line - 1375 rpm and so on up to 6000-7000 rpm.

Notes on this graph - display in air fuel values. Ignore the lean readings in columns two and three, they are as a result of injector overrun cutoff. Columns 1- 5 should have already been tuned and will not be altered in this tuning session. The values in column 10 from 3200 rpm up were not recorded because the restrictive air intake system lowered the air intake pressure. Attention here would improve power.


The aim here is to be smooth. Do not make large changes, but blend changes in 1 - 2 % at a time. Use the 2D map to make sure the fuel transitions are smooth. Ignore overly high or low recorded points (like the 15.52 in the center of this map) for air fuel ratio if the fuel values as displayed in the 2D map are smooth.

Full throttle tuning

Once you have air fuel values broadly correct you will want to concentrate on some full throttle runs and the values in columns 8, 9 and 10. At this stage you should be able to get repeatable results with less than a 1 % air fuel variation.

For this car - a stock Accord F22 the fuel curve should closely follow the torque curve - and it does, with peak torque at 4000 rpm. Note that after peak torque, the engine will need less fuel.

Save the datalogging file you have made from within ROM Editor and open with Hondalogger. Select RPM and Airfuel Ratio as charts.

Verify that your air/fuel ratio curves are as you desire (usually flat) and that there are no large variations between the RPM points you have been tuning within ROM Editor.

VTEC Tuning

Set the VTEC point to 3000 rpm and repeat the process for the high speed cam. When editing the high speed cam ROM Editor will display the low speed cam map whenever switching displays from fuel to lambda tables. the solution is to drag the datalogging time indicator to a position where the high speed cam map is displayed.

Boost tuning

Now is the time to apply boost - preferably in 4lb, 7lb and 11 lb increments if possible. Tune down each of the boost columns. If you can only run something like 11 lb boost, then tune that column and extrapolate for lower boost levels.

This may not be the most efficient way of tuning. If you make improvements to this process let us know.

Tuning is an art and a science - and hopefully fun. Happy tuning.