How to MegaSquirt Your Water Cooled VW

If you haven’t already, please read the ‘disclaimer’ at the top of the parent page here.

Applications:

VW used quite a number of ignition systems on their water cooled engines. This article covers the Hall effect distributor with four teeth, used on most of the ’80s era inline 8V and 16V motors. Later VWs used a 60-2 crank trigger to drive a distributor, or later, distributorless ignition systems. This article covers the older 4 vane distributor and the Bosch 139 module.

Note: We’ve confirmed that the flat four “Wasserboxer” engines as used on Vanagons use a different ignition system. The coil is controlled directly from the ECU, and it is not yet confirmed if the distributor input mods work with the stock distributor. Right now this article is only confirmed to work on inline motors.

With a K-Jetronic (CIS), you will also need to swap your fuel system over to EFI. The other EFI systems – L-Jetronic, Motronic, and Digifant – can use their stock hardware.

The Bosch Hall effect distributors let you use almost any MegaSquirt variant out there.

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 MSExtra.com.

 

Using the MegaSquirt-I (MSnS-E) with the Bosch ignition module

Since there is no need for a VR conditioner or onboard coil driver, this one can use the V2.2, V3.0, or V3.57 board.

MegaSquirt-I PCBv2.2 Mods Required:

  • Remove D5, D8, and R10. Also remove the jumper between XG1 and XG2.
  • Replace D8 with a 1K resistor.
  • Run a length of wire from XG1 to the right hole of D5.
  • Run a wire from the bottom hole of R10 to the top of R11.
  • Run a 750 ohm to 1K, 1/4 watt resistor from the right (5v) side of R23 to the negative (top) leg of D17.
  • Run a wire from the negative leg of D17 to X11.
  • That’s it!

MegaSquirt-I PCBv3.0 Mods Required:

  • Build the Hall effect input conditioner circuit, as described in MSExtra’s MS1 Manual. All our pre-assembled Megasquirts with the V3.0 board come with this circuit installed. However, the jumpers are a bit different:
  • Get a 1K 1/4w resistor and cut the leads down to about 1/2″ at each end. Maybe a bit less.
  • Tin each end of the resistor with a bit of solder.
  • Cut a 5″ piece of hookup wire (22ga is fine) and strip just a 1/8″ or so. Tin the stripped wire with solder.
  • Melt the tinned wire tip to one end of the tinned 1K resistor tip and let it cool.
  • Heatshrink wrap this wire/resistor assembly.
  • Use this wire/resistor combo to connect OptoIn to one of the 5 volt holes in the proto area.
  • Jumper TachSelect to XG1.
  • Jumper TSEL to OptoOut.
  • Solder a 750 ohm to 1K, 1/4 watt resistor from the right (5 volt) leg of R24 to the top (negative) leg of D14.
  • Run a wire from the top leg of D14 to IGN.

That’s it!

MegaSquirt-I PCBv3.57 Mods Required:

  • For this one, you’ll remove the jumpers on XG1 and JP1. Put the jumper on J1 in the 1-2 position for optical output.
  • Get a 1K 1/4w resistor and cut the leads down to about 1/2″ at each end. Maybe a bit less.
  • Tin each end of the resistor with a bit of solder.
  • Cut a 5″ piece of hookup wire (22ga is fine) and strip just a 1/8″ or so. Tin the stripped wire with solder.
  • Melt the tinned wire tip to one end of the tinned 1K resistor tip and let it cool.
  • Heatshrink wrap this wire/resistor assembly.
  • Use this wire/resistor combo to connect pin 3 of the JP1 jumper to one of the 5 volt holes in the proto area.
  • Solder a wire from XG1 to pin 2 of the JP1 jumper.
  • Run a wire from PAD1 to the center hole of Q16.

That’s it!

External Ignition Wiring

  • Connect the signal wire from the Hall effect sensor on the distributor to pin 24 (Tach on the relay board, if used).
  • Connect the #6 pin of the Bosch ignition module to the MegaSquirt’s spark output pin. On a V3.0 or V3.57, this is pin 36. On a V2.2, this is pin 25.

MSnS-E Ignition Configuration

  • Configured for MSnS Spark Output using LED 17 (D14).
  • In MegaTune, you must set Spark Output Inverted to No.
  • Set the Dwell Control mode to Fixed Duty with a 50% duty cycle.
  • The Trigger Angle setting will depend on the physical location of the trigger pickup. Often, an angle of 60 degrees will get you in the ballpark. To set the timing with MSnS-E, go to the Spark Settings menu and set Fixed Angle to 10 degrees. You can then set the ignition timing to 10 degrees with the engine running, using a timing light. Once you have set the base timing, set Fixed Angle to -10. This will tell MSnS-E to use the timing map.

See the MS1/Extra manual on Bosch 139 modules for more information.

 

Using the MegaSquirt-II PCBv3 with the Bosch 139 ignition module

MegaSquirt-II PCBv3.0 Mods Required:

  • Build the Hall effect input conditioner circuit, as described in MSExtra’s MS2 Manual. All our preassembled MegaSquirts with the V3.0 board come with this circuit installed.
  • Jumper TachSelect to OptoIn.
  • Jumper TSEL to OptoOut.
  • Jumper XG1 to XG2.
  • You’ll need a 1K pull-up resistor from the 5 volts in the proto area to TachSelect.
  • Jumper JS10 to IGBTIN.
  • Install a BIP373 or TIP120 in the Q16 slot, using a mica insulator.
  • Jumper IGBTOUT to IGN.
  • Add a 1K pull-up to 5 volts by connecting a 1K resistor from the IGBTOUT-IGN jumper to a 5 volt supply from the proto area.

That’s it!

MegaSquirt-II PCBv3.57 Mods Required:

  • Put the XG1 to XG2 jumper in place across both pins.
  • Put JP1 in the 2-3 position and J1 in the 1-2 position.
  • Solder a 1K resisor across the R57 pads.
  • Jumper JS10 to IGBTIN.
  • Install a BIP373 or TIP120 in the Q16 slot, using a mica insulator.
  • Add a 1K pull-up to 5 volts by connecting a 1K resistor from the center leg of Q16 to a 5 volt supply from the proto area.

That’s it!

External Ignition Wiring

  • Connect the signal wire from the Hall effect sensor on the distributor to pin 24 (Tach on the relay board, if used).
  • Connect the #6 pin of the Bosch ignition module to the MegaSquirt’s pin 36.

Megatune Ignition Configuration:

  • Trigger offset = 60 (this will vary, depending on the distributor orientation, see notes at the end of the article)
  • Ignition Input Capture to ‘Rising Edge’
  • Cranking Trigger to ‘Trigger Return’
  • Coil Charging Scheme to ‘Standard Coil Charging’
  • Spark Output to ‘Going Low (Normal)’

You could optionally switch out your ignition module for the Bosch 124 and use the mods in the manual, or put a BIP373 in the Q16 slot and use direct coil control.

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 TunerStudio  (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 TunerStudio 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.)