MS2-Extra Missing Tooth or Cam Wheel Manual

Only for use with the MS2-Extra code (HC9S12C64 based microprocessor - MS2 Daughter Board)

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NOTE: Please ensure you have one of these daughter boards inside your ECU before continuing. If you have a black microprocessor, then you have an MS1 and these manuals are NOT for MS1 see here for MS1-Extra Manuals

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Please Note:

All of these instructions / diagrams are to be used at your own risk, like most things there is more than one way to do the same thing, what we have tried to do is to offer a method that we have tested or that others have tested for us. No warranty expressed or implied.

Use at your own risk.
If you do have any suggestions or settings that work please let me know Philip.Ringwood(at)

Main Index of MS2-Extra Manuals

Missing tooth crank or cam wheel

Introduction -- Mounting the Wheel and VR sensor -- Sensors and wiring -- Settings

This implementation in MS2/Extra gives up to 6cyl coil-on-plug or up to 12cyl wasted spark.

The wheel decoder allows the use of a multi-toothed trigger wheel such as 36-1 (commonly fitted to Fords), 60-2 (used mainly by Bosch and therefore very widespread in Europe.)
See for a supplier of custom made wheels. Other custom wheels such as 6-1 or 4-1 also work.

The code supports:

Fuel only

Single coil (distributor based setup)

Wasted spark with multiple coils

Coil on Plug (wasted COP)

For wasted spark you require a minimum of single "missing tooth" crank wheel, only engines with an even number of cylinders being supported. You need at least 4-1 for 4cyl, 6-1 for 6cyl or 8-1 for 8cyl. However, the 36-1 wheel is probably the easiest to obtain. The MS2 ECU can drive up to 6 seperate spark outputs, meaning it can run up to 12 cylinders in wasted spark mode.

For Dual Wheels (Cam sensor as well as Crank sensor or 2 Cam sensors, etc) or the Nippondenso CAS used on many Mazda or Toyotas or for real Coil on Plug see Dual Trigger Wheel

The Trigger Wheel system is the most common tach input configuration on Megasquirt by far. The suggested configuration for a retro-fit trigger wheel installation is a 36-1 wheel mounted to the crank pulley and a single-tooth cam wheel if COP or sequential fuel are desired.

Where to mount the sensor and wheel

Lets asume your going to change a distributor based setup over to a wasted spark coil pack setup. The changes needed will be different for each engine but the basics should be the same: A wheel will need to be fitted on the crank pulley, a VR (Variable Reluctor) sensor will need to be mounted to detect the wheel and a set of coil packs will need to be mounted onto the car.

Typical trigger discs (36-1) from a Ford VR Sensor

Mounting the wheel is quite critical in that it MUST be mounted so it rotates without moving up, down, left or right as the sensor needs to see all of the teeth with a gap of 0.75 - 1.0mm.

Fords are a common source of used parts. Almost all models since the 1990s use a suitable VR sensor and coil pack. Be sure to retain the loom connectors too. The VR sensor may be mounted near the crank pulley or reading teeth from the back of the flywheel.

Sensors and wiring

For all ignition pickup / tach inputs, see the tach input page

For all coils and spark outputs, see the spark output page

What is Tooth #1

Make sure you understand this!
With the engine rotating in the normal direction...

Tooth #1 is the first tooth to pass the sensor after the missing tooth gap.

We use the term "tooth#1" as it is consistent across wheels with one, two, three or four missing teeth in the group.
Once the code knows the tooth#1 angle it automatically calculates other needed information internally. (No need to manually enter trigger teeth or delay teeth etc.)

Clockwise rotation (normal) - method a

Set your engine at TDC, then count the number of GAPS to tooth#1 in the direction of rotation (clockwise here) and multiply by the angular size of the tooth.
e.g. 8 teeth * 10 deg per tooth = 80 deg
36-1 wheels are 10 deg per tooth (360 deg / 36 teeth)
60-2 wheels are 6 deg per tooth (360 deg / 60 teeth)
24-2 wheels are 15 deg per tooth (360 deg / 24 teeth)

Clockwise rotation (normal) - method b

A different way of looking at the SAME phasing.
Turn your engine so that tooth #1 aligns with the sensor. Read off the tooth#1 angle from timing marks/tape on the crank pulley.


e.g. Typical Ford Setup:
       36 -1 setup is 10deg between teeth (360deg / 36 teeth = 10deg)

       Tooth 9 lines up with sensor at TDC, so tooth 9 to tooth 1 = 8 teeth
       Therefore 8 teeth x 10deg = 80deg (Tooth #1 Angle)

      Typical Vauxhall/Peugeot (and other Bosch) setup
       60-2 setup is 6deg between teeth (360deg / 60 teeth = 6 deg)
      Tooth number 20 lines up with sensor at TDC, so tooth 20 to 1 = 19 teeth
      Therefore 19 teeth x 6deg = 114deg (Tooth #1 Angle)

Ignition Options for Toothed Wheel
36-1 wheel setup in Trigger Wheel Settings

For most installs set the Ignition Capture to Rising Edge. See the Ignition Input options HERE.

If using VB921's to directly fire the coils set the Spark Output to Going High (Inverted)

The Number of Coils is simply dependent on your coil setup. If you have coil packs, 1 coil firing 2 cylinders, (so 2 coils on a 4cy or 4 coils on a V8) then select Wasted Spark. If you have a distributor then select Single Coil, if you have Coil on Plugs (4cy engines ONLY) select Coil on Plug. Dual Dizzy is for setups with 2 distributors (e.g. Lexus)

If you have a question, comment, or suggestion for this FAQ please post it on the forum.

No part of this manual may be reproduced or changed without written permission from James Murray, Ken Culver and Philip Ringwood.

Based on the original MegaSquirt® tuning guide: ©2008 Bowling and Grippo. Used with permission.