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Old 17-09-2015   #1
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Testing the crankshaft sensor at the ECU Plug

I thought this would be an interesting thing to do.

My sensor is the two wire inductance or coil of wire type. A three wire sensor would need a different testing arrangement because it has built in electronics which have to be fed with a reference voltage.

My sensor was marked with Bosch Germany, 485450A and 0 281210238. This particular sensor has the plug directly on the sensor rather than having the extension wire and then the plug.

My ECU is MEH73H4F001

Resistance at the sensor was 931 ohms. While measuring resistance, metal brought very near the sensor would make big changes to the resistance.

The two sensor wires are a slightly twisted red and white pair. Taking both of the ECU plugs off it was fairly easy to work out the twisted red and white were in the plug nearest the windscreen. I then used a Light emitting diode or LED with a resistor in series connected to the battery to trace the wires to the correct part of the plug. I suppose any old bulb would have done the job but if I messed things the higher current could have damaged something somehow.

I made up a test lead from an audio cable that would fit into my lap top and used the wires from a diode for the ECU test points. The resistance at the end of my cable was 928ohms. Using freeware audacity sound editing software when I cranked the engine with the starter I got a solid block of pulses which I was able to slow down with the editing software to reveal the square wave the sensor was producing.

http://sourceforge.net/projects/audacity/

The sensor was able to pulse a LED even when it had the resistance in series quite easily. (my diy test LED with the resistor, glows visibly when on 12V - the idea being to have a test method that draws very little current)

The A/C voltage was 3.49V
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Last edited by judderbar; 17-09-2015 at 14:43.
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Old 18-09-2015   #2
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Re: Testing the crankshaft sensor at the ECU Plug

Oops. My ECU is ME73H4F001

The old eyes are not what they used to be.
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Old 18-09-2015   #3
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Re: Testing the crankshaft sensor at the ECU

Nice Clear scope of the minor degree markers - you can also see the variation where the TDC mark is

Ziggy
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Old 18-09-2015   #4
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Re: Testing the crankshaft sensor at the ECU

Quote Originally Posted by Ziggy122 View Post
Nice Clear scope of the minor degree markers - you can also see the variation where the TDC mark is

Ziggy
It was recorded and analysed as an audio file. So I have a record of every signal the sensor produced. Using the same recorded file I just measured the time difference for each rotation and they are almost identical suggesting the compressions are all equal. A bit nerdy but it was quite interesting

A possible next project will be to feed the audio file to the ECU and do a video of the injector noise with the fuel pump relay pulled out. I am guessing it will sound a bit like a sewing machine impersonating a starter motor.
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Last edited by judderbar; 18-09-2015 at 17:09.
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