How to MegaSquirt your Honda



Models covered:
All 1992-2000 Civics, Del Sols, and Integras
1992-2001 Prelude
1992-2002 Accord four cylinder models

This covers many of the popular Honda four cylinder engines, including the D16 family, B16A, B18C, H22A, and F23A. It does not cover later coil on plug ignition systems such as the ones used on the S2000 or D17 powered Civics.



What's covered in this article

Note that our tech 'Install Articles' typically focus on the most confusing part of the install process for the end user, and that's taking control of the ignition system. This is the part of the process that's different from car to car and hence we chime in with specifics to help where we can. For the rest of the details, the parts that are the same on every car like the coolant, intake, TPS, and o2 sensors, see the wiring section of the MegaManual.



Honda's distributor design
Honda used a similar set of electronics across their model range during the '90s. These designs use three separate VR sensors called CYL or CYP, TDC, and Crank or CKP. These produce 1, 4, and 24 pulses per camshaft revolution. Usually all four sensors are in the distributor, but some F and H series motors locate the TDC and CKP sensors on the crankshaft instead. There are a number of different ways you can use these sensors, but by far the easiest way is to use the TDC sensor and simply ignore the other two. The colors Honda used for the TDC sensor vary from year to year and model to model. The most common color schemes appear to be orange and blue for the positive wire and white and blue for the negative wire, or green for the positive wire and red for the negative wire. The factory wiring diagram will always show this sensor as the TDC sensor.

The ignition module in these cars lets current flow through the coil when the input is grounded. When the coil is not charging, the voltage is slightly above 5 volts, which is reflected in the circuit shown here.


Using the MegaSquirt-II PCBv3 with the Honda ignition module

MegaSquirt-II PCBv3.0 Mods Required:

Build the VR conditioner circuit, as described in Step 51 of the MegaManual. All our preassembled Megasquirts with the V3.0 board come with this circuit installed.
Jumper TachSelect to VRIN.
Jumper TSEL to VROUTINV.
You may need to adjust the VR trim pots, R52 and R56, when this is installed on a running engine. A usual _base_ setting is to turn them all the way counterclockwise.
Jumper JS10 to IGBTIN and IGBTOUT to IGN.
Install a TIP120 or similar switching transistor in the Q16 slot. You will not be using this to drive the coil directly so you do not need a transistor meant for serving as an ignition module, although an ignition transistor like a BIP373 will work too.
To create the appropriate pull-up, you will need to wire a 1K resistor from a 5 volt source such as the 5 volt holes in the proto area and a 4.7K resistor from a 12 volt source, and run both of these to the IGBTOUT-IGN jumper.
That's it!

MegaSquirt-II PCBv3.57 Mods Required:
Put the JP1 jumper in the 1-2 position and J1 in the 5-6 position.
You may need to adjust the VR trim pots, R52 and R56, when this is installed on a running engine. A usual _base_ setting is to turn them all the way counterclockwise. Note that the trim pots on these boards do not click - giving them 5 counterclockwise turns will make sure they have been turned far enough.
Jumper JS10 to IGBTIN.
Install a TIP120 or similar switching transistor in the Q16 slot. You will not be using this to drive the coil directly so you do not need a transistor meant for serving as an ignition module, although an ignition transistor like a BIP373 will work too.
To create the appropriate pull-up, you will need to wire a 1K resistor from a 5 volt source such as the 5 volt holes in the proto area and a 4.7K resistor from a 12 volt source, and run both of these to the middle leg of Q16.
That's it!

External Ignition Wiring
Wire the TDC positive signal to pin 24 on the Megasquirt, and ground the negative wire from this sensor. On our preassembled wiring harness, you can use the shield on the IGN wire as a ground.
Wire the Honda ignition module input to pin 36 on the Megasquirt.
Megatune Ignition Configuration:
Trigger offset = 10° (this will vary, depending on the distributor orientation, see notes at the end of the article)
Ignition Input Capture to 'Falling Edge'
Cranking Trigger to 'Trigger Rise'
Coil Charging Scheme to 'Standard Coil Charging'
Spark Output to 'Going High (Inverted)'
Set the dwell to 3.0 ms.

More information on setting Trigger Offset:
You must also set the initial position of the trigger (called the 'trigger offset'), then check it using the Trigger Wizard in MegaTune (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you'll need to set it properly... Basically you use the Trigger Wizard and adjust the 'trigger offset' and/or twist your distributor until the advance number in the Trigger Wizard matches what you're reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You'll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up.

Here's the information on this direct from the MegaTune Manual:

Before tuning your advance table, be sure to use a timing light to verify that your 'trigger offset' is calibrated. Changing the Trigger Offset in MegaTune will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match.

To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in MegaTune. (8° in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.


IAC Valves
These Hondas all used a PWM IAC valve. This valve runs at a frequency around 500 Hz, so in MS1/Extra you will need to set the frequency to 20, while in MS2 Bowling & Grippo code you enter the number 500 directly. V3.57 boards need no modifications to control this valve, while V2.2 and V3.0 boards will need a TIP120 transistor, like the one included in our MK-PWMIAC mod kit.

VTEC control
While the ECU normally grounds devices to activate them, the VTEC solenoid gets 12 volt power from the factory ECU. The easiest way to control this is to add a relay control circuit to the Megasquirt and use a relay to power the VTEC control circuit. With Megsaquirt-I, you will just set the RPM where it activates, while Megasquirt-II also lets you set a minimum throttle position at the same time.

Suggested parts
For a good basic installation, the Megasquirt-I V3.0 (or V3.57) will meet your needs. The Megasquirt-II is a good upgrade if you want the latest and greatest, particularly if you're running very large injectors. You will be able to use your existing sensors except for the MAP sensor which is built into the Megasquirt.