How to Control IAB's on P06/P28 with Neptune

The factory P72 (94-95 OBD1 Integra GSR) ECU's have built-in IAB (intake air bypass) control circuitry. This allows the P72 ECU to control IAB operation for optimum engine torque and power output at varying engine rpm. When using the Neptune/Demon setup in a P72 ECU, the IAB's can function normally and the IAB operation can be controlled within the software without any changes.

However, when using the Neptune/Demon setup in a non P72 ECU (ie: P06, P28 ECU, etc.), the factory IAB operation is not possible as these ECU's do not have IAB circuitry within the ECU. Thankfully, the Neptune software is very flexible and allows IAB operation with a small wiring change and software configuration.

The factory OBD1 Integra GSR B18C1 IAB control solenoid has a 2-pin connector. One wire (yellow w/black stripe) supplies +12v to the solenoid, while the other wire (pink w/blue stripe) goes to OBD1 ECU pin A17 on the P72 GSR ECU. This pink with blue stripe wire is the ECU's IAB control solenoid wire.

The factory purge control solenoid on OBD1 ECU's (all P06, P28, P72, etc.) also have a 2-pin connector with one wire (yellow w/black stipe) supplying +12v to the solenoid and the other wire (red) connecting to OBD1 ECU pin A20. This red wire is the OBD1 ECU's purge control solenoid control wire.

Since both the IAB control solenoid and purge control solenoid use the same power and control style, we can retask the ECU's purge control solenoid output to control the IAB's easily.

The first step is a wiring change:

If you are working on a 94-95 integra with original B18C1 engine and wiring harness, simply complete the following:


  • Remove the red wire at pin A20 from the ECU connector and tape it off.
  • Move the pink with blue stripe wire from pin A17 to the now empty slot at pin A20.


If you are working on any other vehicle without the factory IAB/GSR engine wiring harness, complete the following:


  • Disconnect the 2-pin connector from the purge control solenoid valve and plug it into the IAB solenoid control valve. You may need to extend the wires as needed for the connector to reach.


The next step is a software/calibration configuration change within Neptune:

Within your calibration/tune file, go to "parameters" > "outputs" > "output 1" and set the output parameters as shown:



This will setup your ECU to now use the purge control solenoid control pin to run your IAB's. Not only can you now control IAB's through your non-P72 ECU, but you will have enhanced control over IAB operation using the "conditions" and "adjustments" fields:



The stock OBD1 P72 ECU for the B18C1 engine powers the IAB control solenoid to hold the IAB's closed. When it opens the circuit (no power), the IAB's then open.

The stock OBD1 P72 ECU for the B18C1 holds the IAB's closed until 5750 rpm. Above 5750 rpm the ECU opens the IAB circuit to allow the IAB's to open for high rpm power. Once the engine rpm drops back down below 5450 rpm, the ECU closes the circuit which powers the IAB solenoid and closes the IAB's again for low rpm torque.

You can use the Neptune's "conditions" and "adjustments" field as shown above to configure the IAB operation as you wish for the best performance.