Cam and Crank Angle Sensors

[free5ty1e]

While perusing the Engine & Wiring Service Manual scans in preparation for the next verison of the LegacEBC/LegaCU, I've come across some signals I'm not quite sure how to process:

On the camshaft / cam angle sensor (page 191, figure 71), there appears to be a Hall-effect (magnetic pickup) sensor that detects something on the camshaft sprocket. They appear to be notches, at 12, 3, 6, and 9 o'clock, in a respective pattern of one large, two small, one large, three small. These seem to represent the pulses we would see on an oscilloscope; this diagram appears to makes sense, as the order of the pulse lengths received would allow tracking of the cam angle. (if I'm wrong, tell me please)

The crank angle sensor on page 187 (figure 68), however, is not quite as straightforward; schematically, no indication is given as to how it works. Does anyone have experience with reading the crank angle sensor? I can't fathom the relationship implied by this drawing.

[Legacy777]

The crank sensor is going to do the same thing, except more accurately. The ECU is mainly concerned about the crank position. The timing belt gear that goes on the crank has intermittant spaced teeth that register with the sensor and cause a pulse to be sent to the ECU.

The primary function of the cam sensor is to tell the ECU when the #1 piston is at TDC. With this information of knowing where the crank is, and where the #1 piston is, the ECU can then set ignition timing advance/retard/dwell.

You shouldn't really need to do anything with the cam or crank signals. If you want to read engine rpm, you can tap into the ignition leads or the tachometer output signal that goes to the TCU.

If you use the ignition leads for rpm, you will need to cut the signal in half since our ignition is wasted spark and fires twice per cycle.

[vrg3]

Not Hall effect. Variable reluctance.

The camshaft position sensor doesn't really report the angle of the camshaft... I would say it's better described as Subaru sometimes refers to it -- as a cylinder discrimination signal. It allows the ECU to figure out which cylinder is going to fire next, so it knows which channel to spark and which injector to pulse when running sequentially.

The crankshaft position sensor is used to measure angles, though. It has three pips per 180 degrees of crankshaft revolution, the reading of which allows the ECU to determine where in the compression stroke the firing cylinder is. There is one pip at 97 degrees BTDC, one at 65 degrees BTDC, and one at 10 degrees BTDC.

[Kelly]

Your fucking spot on.

Unfortunatelly, Subaru was one of the only companies to use this setup, which makes finding standalone units programmed to understand it a pain in the bum. Everyone else used 60-2, +1 on the cam. Why Subaru, why?...............

[NICO]

subaru is crazy but they take a good ass kicking and they dont give up.

all most for got there like legos which i love to build crazy stuff

[free5ty1e]

Thanks for the responses guys, that makes a little more sense now. This is not for a tachometer, I already have one worked out based on the ignition signal cut in half. This is for future development on the LegaCU - for timing control. If I want a product that's capable of retarding and advancing the signal, I'll need more than just the ignitor.

I'm not prepared to begin working with these signals just yet, but I will probably have some more questions once I begin. For now, just redesigning the PCB and the overall configuration of the LegacEBC / LegaCU to support everything I have planned for it.

Kelly - you seem to be familiar with the "standard" setup that most aftermarket units know about and support. While these products will be originally for Legacy vehicles, I will eventually want to add support for these standard setups. Is that the main difference, the info in your post...?