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
- 2 Wideband O2 cable
- 3 0-5V Output from wideband to stock
- 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
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
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.
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
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
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
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.
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
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.
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.
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.