Crankshaft Position Sensors and OE ECM Solutions

Tougher California Air Resources Board and EPA standards are prompting most V-twin engine manufacturers to transition to more advanced engine control modules (ECM). These systems will require a crankshaft position sensor for accurate ignition timing and for future incorporation of fuel injection. To assist the industry in this transition, we have compiled relevant technical information including a list of sensor suppliers.   


Sensor Types  

Magnetic gear tooth type sensors are generally used for crankshaft position sensing. Gear tooth sensors detect the presence of a ferrous (iron) metal target. The sensor contains a biasing magnet. As the ferrous target (i.e. tooth on the crankshaft) passes over the sensor, it affects the local magnetic field. The sensing element detects the change in the magnetic field and generates an output signal. 

Magnetic gear tooth sensors only work with a soft iron target. They cannot detect the presence of non-magnetic materials such as plastic, copper, brass, aluminum, or most stainless steel alloys. They function best when they are mounted in a non-magnetic housing. The typical motorcycle application where the sensor is mounted in an aluminum alloy crankcase and detects teeth on a forged steel crankshaft is an ideal situation for this type of sensor.  

Gear tooth sensors fall into two main categories: variable reluctance and Hall Effect. Both sensor technologies have been widely and successfully applied for many years in the automotive industry. Tradeoffs are summarized in the following table:


  Hall Effect Variable Reluctance (VR)
RPM range Zero RPM sensing. Signal level unaffected by RPM. Minimum RPM. Signal level proportional to RPM. Must consider if signal level will trigger ECM under worst case cranking conditions 
Signal output Digital 0-5V square wave Analog sine wave. Peak-peak voltage level proportional to RPM. Requires signal conditioning in ECM. 
Noise immunity High Acceptable
Technology Semiconductor Hall Effect element with built-in signal conditioning Simple coil winding. Most rugged construction possible
Electrical Interface Typically 3-wire (power, signal output, and ground) 2-wire (signal and signal return)
Temperature range -40 to +150C typical. Semiconductor element may fail at higher temperatures  -40 to +150C typical. Usually survives higher temperatures


All variable reluctance sensor applications require careful analysis and testing of the worst case signal output under cranking conditions. This includes consideration of worse case sensor air gap due to manufacturing tolerances, low battery voltage, and cold temperature conditions. Some smaller engine manufacturers  may be ill equipped to perform the necessary analysis and testing. In this case, we suggest application of a Hall Effect sensor.


Typical Crankshaft Position Sensors


Two typical crankshaft position sensors suitable for motorcycle applications are shown above. The sensor on the left  is the OE H-D P/N 32707-01 used on late model Twin-Cam engines. The part on the right is a Honeywell VR (variable reluctance) sensor. These two parts are used to illustrate general requirements: wire harness pigtail or integral connector, mounting bracket, and O-ring seal. All the suggested sensors have similar constructions and dimensions. Other industrial sensors using screw thread type housings are available, but not suitable for engine applications due to difficulties in sealing threads and setting the correct air gap. 


Sensor Waveforms  

Typical VR and Hall Effect sensor waveforms are shown below. The VR sensor generates a sinewave signal with amplitude proportional to RPM. It does not require an external power source. Minimum signal requirement to trigger the ECM is 1 volt peak-peak with a 2.7K Ohm load on the sensor output. Hall Effect sensors always require an external power supply and pull-up resistor. Hall Effect sensors are capable of zero-speed sensing and the signal output is a square wave with amplitude independent of RPM. 

Proper air gap between the sensor and crank trigger wheel is required. A nominal air gap of .030" is common. You must consider manufacturing tolerances, thermal expansion effects, and run out. For a VR sensor, the signal amplitude will rapidly decrease as the air gap increases. For a Hall Effect sensor, the signal will become erratic and then disappear when a critical air gap is exceeded. You must observe and confirm the signal waveforms. You can visit our Diagnostic Tools Tech FAQ for advice on suggested test equipment.



Crankshaft Position Sensor Waveforms


Crankshaft Position Sensor System Design  

To be compatible with existing engine control modules for Twin Cam applications, the crankshaft position (CKP) sensor system must have 32 teeth (30 actual and 2 missing)  and the same timing relationship as the OE H-D design. We have included a PDF file that shows the required timing relationship.

 Crankshaft Position Sensor Timing Chart


Establishing the required timing relationship between the sensor and trigger wheel is a complicated process and some trial and error experimentation will be required. The sensor waveform and timing chart information we have presented above can serve as a starting point. Once the components are mounted on the engine, you can connect a Daytona Twin Tec TC88A series ignition modules and use a timing light. When you crank the engine, the ignition fires at TDC. You will probably have to "fine tune" the sensor location or angular orientation of the crank trigger wheel. 

If you have questions, call us. While we are pleased to provide our customers with free technical assistance, crankshaft position sensor system design is best left to engine manufacturers. We cannot respond to inquiries from experimenters seeking to convert individual engines.   


Sensor Suppliers  

The table below lists the major suppliers that we have been able to identify. With the exception of Optek, all of these companies will provide off-the-shelf sensors in reasonable quantities. We do not make any particular recommendation. Engine manufacturers are urged to contact the suppliers, request sample parts, and make their own evaluation.  


Supplier Contact Website
AEC (American Electronic Components)

Julian Wells

574-264-6099 x439

Art Leeper


Jim Hickman


Koji Moroshita

734-529-5525 x127

Gayle Bradford

Optek (custom parts only)

Tom Osbourne


SSI (OE supplier for


Kerry Bensing


Greg Kiproff



Sensor Data Sheets and Application Notes  

We have compiled data sheets and application notes for applicable gear tooth sensors from the vendors listed above. The Honeywell application notes (Introduction to VR Sensors and Hall Effect Sensing Chapters 1-7) are particularly useful. The compilation is in the form of a ZIP archive file that you can download by clicking on the link below. You will require PKZIP to unzip the individual files within the archive. If you do not have PKZIP installed on your computer, you can download it from the PKWARE Inc. website.

Sensor Data Sheets and Application Notes


OE ECM Solutions  

We can supply turnkey ECM solutions to engine or vehicle manufacturers seeking to incorporate crankshaft position sensor systems. For carbureted engines, we can supply a non-adjustable OE version of our TC88A ignition module. The TC88A-OE can be configured for either a VR or Hall Effect type CKP sensor and can be programmed with any required ignition advance and RPM limit characteristics. The TC88A-OE includes diagnostics, built-in data logging, engine operating statistics, and J1850 data bus compatibility. For fuel injected engines, we can supply an OE version of our TCFI series fuel injection controllers. The TCFI can operate in closed loop using feedback from oxygen sensors or open loop with a predetermined fuel calibration. All TCFI units include diagnostics, built-in data logging, and engine operating statistics. The TCFI Gen 4 has a J1850 data bus and the TCFI Gen 5 has a CAN data bus. We provide Windows software that allows an engine manufacturer to easily program units for particular applications. Units are available off-the-shelf without any tooling or engineering charges for most applications. We have included a wiring diagram that shows a typical TC88-OE application. You can also use this wiring diagram for custom bike applications with standard TC88A units. Please contact us for more details. You can also visit the TC88A and TCFI Gen 4 and TCFI Gen 5 web pages.    

TC88A-OE Wiring Diagram (PDF File)


TC88A-OE Ignition Module

TCFI Gen 4 Fuel Injection Controller  (Shown with Optional WEGO Wide-Band System)

TCFI Gen 5 Fuel Injection Controller