Why two HES's?

K7GLE · Apr 12, 2018

This will probably turn into a "doh!" after I get the first answer, but I'm used to being wrong (married 35 years) so here goes:

What is the purpose of the second HES 180 degrees apart from the other? Both plugs fire at the same time, based on the one at 360, right? It seems the Motronic could calculate RPM and crank position based on just one. Is it just to provide a higher resolution calculation?

kioolt · Apr 12, 2018

I've never given this much thought before so I may be wrong in my answer. I believe that the HES is on the end of the camshaft which turns at 1/2 the speed of the crankshaft. The plugs fire each time the cylinder hits TDC even if it's an exhaust stroke. If the above are true wouldn't you need two HES's to get a spark each time either cylinder hits TDC?

gsaddict · Apr 12, 2018

The upper sensor is the spark signal (wasted)
The lower sensor is the fuel injection signal.

jagarra · Apr 12, 2018

One fires the plug's, the other pulses the fuel injection/motronic system.

K7GLE · Apr 12, 2018

Thanks. I assume there is a reason they couldn't / shouldn't have used a single sensor for both.

442bmw · Apr 12, 2018

K7GLE said:
Thanks. I assume there is a reason they couldn't / shouldn't have used a single sensor for both.

If yours is old,,replace it or have it rebuilt,,it will strand you one day,,gsaddict will hook you up,

K7GLE · Apr 13, 2018

442bmw said:
If yours is old,,replace it or have it rebuilt,,it will strand you one day,,gsaddict will hook you up,

Thanks - Already done.

Why two HES's?

K7GLE

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442bmw

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