How To… Clamping The MAF or MAP Signal

How To… Clamping The MAF or MAP Sensor Signal

If you want to add a turbo or supercharger to an engine or raise the boost on a factory equipped turbo engine, you might have to clamp the signals of the MAF or MAP sensors. Most modern ECU’s monitor the load signals and if they are bigger or smaller than the expected signal at various RPM points, the ECU will go into “limp-home” mode and ignore the signal and set a check engine light.

By “clamping” the signal the Unichip will not allow the output to go over a certain specified value. With the version Q Unichip you can clamp the fuel and TPS output signals by simply typing values in the clamp map’s and activating the voltage clamp’s. To do this open the Fuel or  TPS map and click on the corresponding (Fuel or TPS) “Map Setup”

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Once the clamp is active you can type the clamp values directly into the bottom row on the map and download the map to the Unichip. In most cases this will be somewhere between 1.2 volts and 4.7 volts on a MAF sensor.  On a MAP sensor signal the sensors will normally be happy with the same value at all RPM points, typically just below 5.0 volts.

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In the example above the fuel signal will not be allowed to go over a value of 4.6 volts. Asan example, if the input is at 4.9 volts the Unichip will not allow the output to go over 4.6volts. On some modern engines the MAF sensor signal is checked at different RPM points. Say at 3000 RPM the standard engine’s MAF sensor typically makes a voltage of about 3.6 volts at full throttle the ECU will see any signal much bigger than 3.6 volts as an error at 3000 RPM.

There will typically be some percentage tolerance that the ECU will allow before throwing thecheck engine code. In order to supercharge or turbo-charge these types of engines the signal has to be clamped at different values at the various RPM points. It is easy to know at what value the standard ECU voltages are at the different RPM points if you can use the “learn clamps” function.

You have to do this step while the engine is still stock (unmodified). To do this on the Menu got to “Tools >> Learn Clamps”  to open the “log data” window. At first it will not have any values in it. Simply drive the engine at full throttle on a loaded dynamometer. Let the engine work throughout the RPM range at full load (full throttle). The maximum voltage the Unichip sees on any of the 5 inputs will be recorded at the various RPM points on the screen.

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You can repeat the procedure as many times as you like as long as the logging window is open. The program will continuously put the highest values it sees in the various RPM points.You can also do this step on the road but it is obviously dangerous to drive a vehicle at fullpower while looking at a laptop screen.

Take a passenger to hold and monitor the laptop if you do so. You will probably drive the vehicle in 4th gear starting with full throttle at low RPM. The data is updated about 3 times per second and if you use to low a gear (like 2nd) the engine will pass through the RPM points too quickly and you might miss or get inaccurate data.

Once you are happy that all the RPM points have the correct values select which clamp map you are using and want to copy the values to. Click on “copy” and the program will copy all the values into the chosen clamp map as well as switch the clamp on for that output.

Unichip map download tip


If the vehicle stall or don’t want to rev up after the you learned the clamp values then you have the manually increase the clamp value at from the lowest RPM point to about 2200 RPM where the vehicle will not make boost.

Clamping Frequency Based Sensor Signals

If the engine uses a frequency based MAP or MAF sensor (like many Mitsubishis) you will be using option 3, 4, or 5 to control the fueling. If any of these options are set to“frequency fuel” the program will also log the frequency data for that option and in the same way the frequency fuel value may be clamped.

If no option is set for “frequency Fuelmap” the frequency columns are grey and no values are recorded to them. You may click on “Clear” to clear all the values and start again. Once you have clicked on ‘Copy” and are finished click the “close” button. Go to the clamp map of the output you are using. If you are clamping the fuel signal you will go to the fuel map, if you are clamping the TPS map you will go there to see the clamp map.

If you are clamping a frequency fuel value you will go to the option you are using to do so. The copy function will only copy values to the map where it logged data. It will write 0 as number in all other map positions. If for an example it didn’t record any values at 500 RPM the program will write a value of 0 in the 500 RPM column and the engine WILL give problems!

Simply look at the clamp map and put logical values in the map whereverit has 0’s as a number. Normally you can make the clamp values slightly higher than the recorded values. You can select the row with the clamp values and use the multiply function to make it bigger by a percentage. It will depend on the specific vehicle as to how high values it will tolerate.

Unichip TPS vs Fuel Clamp

The clamp on the fuel out pin is a mechanical circuit and more accurate than the clamp on the TPS out pin. The TPS pin uses a software clamp. We normally use the fuel circuit for the MAF sensor and the TPS pin to clamp MAP sensors if the engine has both and they all need clamping.

If it only has a MAP sensor it is fine to clamp it using the fuel out pin. The downside of the hardware clamp is that it will not allow the output voltage to go over 5 volts even if the clamp is switched off.

Unichip map download tip Tip!
The Fuel Clamp will always clamp the Fuel output at 5.0 volts even if the clamp is turned of. If you need to work with signals higher than 5 volts then you need to use the TPS clamp.

On some old engines that have VAF sensors that work above 5 volts you have to use the  TPS in and out ports to modify the fueling on these. The TPS output will make whatever voltage it sees on the input (up to 12 volts) and add or subtract from the output whatever value is in the TPS map. The clamp can however not work over 5 volts as a maximum number.