Pick ups

Crank Sensor

The crank sensor needs to see 4 pulses, 5 degrees wide, every 90 degrees with the centers aligned at TDC / 90' BTDC. The lugs need to be accurately machined as their positions are the references for all ignition angles / timings. When cranking (below 457rpm) or running at 0' advance then the TDC lugs are the ref, otherwise the 90' BTDC lugs are used as the start point for the countdown time to ignition. Their heights should also be exactly the same as at very low rpm the amplitude of the signal is low and a larger gap could cause a loss of a pulse.


The standard cosworth pulley has the 4 lugs cast into it. The notch on the rhs is the 16' btdc ref mark.

Phase Sensor

The phase sensor needs to see 2 pulses about 5 degrees wide spaced 180 crank degrees (90 cam degrees) apart with the first occurring about 45 degrees after TDC on cylinder 1. These pulses are not as critical as the crank ones as they are not used as ignition timing references. They are used to tell the ecu which crank pulse is TDC and which is 90' BTDC and on which cylinder. The sensor can be mounted on any shaft running at half engine speed i.e. distributor or camshaft.


If the sensor is mounted inside the distributor, like on the cosworth, then the small diameter will lead to a reduced voltage output unless a sensitive pick up is used and the gap reduced to 0.2 - 0.3mm.



The diagram below shows the relationship between the two pick ups.


Fitting sensors to engine

The following pictures show the sensors mounted on my Ford 2.0 SOHC turbo running cosworth management.

The standard crank sensor is mounted on a bracket which uses the sump mounting bolts to locate it. One of the 4 equidistant lugs is circled above.

Due to a lack of space, the ignition has been converted to distributorless, so the camshaft pulley has been used as the mounting point for the 2 cam reference lugs (which can be seen circled above). A standard cam sensor from a Ford Fiesta Zetec engine has been mounted on a bracket using the cam cover mounting bolts to locate it.

This type of pick up arrangement, using the cam pulley, is common on Escort Turbo conversions. Another method, which has been used, is to mount the top of a cosworth distributor on the top of the standard distributor but it does involve some machining and alloy welding.

As long as the engine 'sees' the correct pulses, in the correct order, at the correct time, it does not matter where they derive from.