Testing the 928 engine speed sensor
11-22-2004, 03:21 PM
#1
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Testing the 928 engine speed sensor
This post provides instructions how to test the inductive engine speed sensor and spark module signal output. These are good tests for no-start and no spark conditions.
The EZF and EZK spark module obtain engine speed information from an inductive pulse sensor, part number 944.606.115.00. It has three connections, (+), (-), and shield (which is grounded).
Applicable Model Years (MY)
EZF spark control is used on Euro/ROW 928s MY 1984 – 1986, US-Spec MY 1985 – 1986.
EZK spark control is used on all 928s from MY 1987 – 1995.
Spark Module Connector Pin Assignment
The sensor pins are connected to the spark modules as follows:
EZF Connector (25 pin): Speed sensor (+) pin 7, Speed Sensor (-) pin 19, Speed sensor shielding pin 20.
EZK Connector (35 pin): Speed sensor (+) pin 23, Speed Sensor (-) pin 6, Speed sensor shielding pin 24.
Remove the spark controller connector from the spark module.
The fuel injection and spark control modules are located in the passenger side “kick panel” on left hand drive cars.
The first test to perform is a resistance test.
a. Set a VOM to measure resistance. Place the leads on the connector pin slots for speed sensor (+) and (-), the resistance reading should be between 600 - 1600 Ohms.
b. Test the resistance between shield and (+), the value should be infinite Ohms (an open circuit).
c. Test the shielding. The test is accomplished by measuring the resistance between the outer case of the sensor and the “shield” lead of the sensor connector to the wiring harness. Remove the speed sensor from the car. Place one lead of the VOM on the connector pin for the speed sensor shielding and the other lead on the outer case of the sensor. The resistance reading should be zero Ohms.
If any of the resistance tests show out of range resistance readings, the speed sensor should be replaced.
Sensor voltage output test.
The voltage output of an inductive sensor varies with RPM, the lower the RPM the lower the voltage. It is best to use an oscilloscope to observe these of signals. There are some inexpensive add-on oscilloscopes for laptop PCs. If you don't have access to an oscilloscope, testing on the DC scale of a voltmeter isn't accurate but you may see some needle twitch. When testing the sensor with a voltmeter it is best to use an analog AC Volt gauge. Set it at the AC 20V scale to begin with and then decrease the scale if necessary to see voltage information.
Crank the engine and note the voltage reading. The minimum output of an inductive engine speed sensor is 3V (AC) when cranking the engine. Some non-Porsche ECU-s need much more (20V) to recognize the inductive signal. If a test is performed when engine is running or somehow cranking at higher speeds switch it to the 200V scale. An inductive sensor can output a total voltage of 120 Volts when triggered at high rpm. Be careful, these are high voltages!
If the minimum voltage output is not obtained, the speed sensor should be replaced.
Place the connector back onto the spark module
Disconnect the LH connector
Test for spark module output
IF the engine speed sensor tests OK, the next test is to determine of the spark module is outputting a speed signal to the LH module for RPM information. The spark module output voltage is measured at LH pin 1 for all 928 LH module types. Crank the engine and note the voltage reading. This signal must be at least 7V, alternating between 0 and 7V in a square wave proportional to engine RPM. Voltmeters may have trouble providing accurate readings with square waves, so an oscilloscope is needed for an accurate test.
The EZF and EZK spark module obtain engine speed information from an inductive pulse sensor, part number 944.606.115.00. It has three connections, (+), (-), and shield (which is grounded).
Applicable Model Years (MY)
EZF spark control is used on Euro/ROW 928s MY 1984 – 1986, US-Spec MY 1985 – 1986.
EZK spark control is used on all 928s from MY 1987 – 1995.
Spark Module Connector Pin Assignment
The sensor pins are connected to the spark modules as follows:
EZF Connector (25 pin): Speed sensor (+) pin 7, Speed Sensor (-) pin 19, Speed sensor shielding pin 20.
EZK Connector (35 pin): Speed sensor (+) pin 23, Speed Sensor (-) pin 6, Speed sensor shielding pin 24.
Remove the spark controller connector from the spark module.
The fuel injection and spark control modules are located in the passenger side “kick panel” on left hand drive cars.
The first test to perform is a resistance test.
a. Set a VOM to measure resistance. Place the leads on the connector pin slots for speed sensor (+) and (-), the resistance reading should be between 600 - 1600 Ohms.
b. Test the resistance between shield and (+), the value should be infinite Ohms (an open circuit).
c. Test the shielding. The test is accomplished by measuring the resistance between the outer case of the sensor and the “shield” lead of the sensor connector to the wiring harness. Remove the speed sensor from the car. Place one lead of the VOM on the connector pin for the speed sensor shielding and the other lead on the outer case of the sensor. The resistance reading should be zero Ohms.
If any of the resistance tests show out of range resistance readings, the speed sensor should be replaced.
Sensor voltage output test.
The voltage output of an inductive sensor varies with RPM, the lower the RPM the lower the voltage. It is best to use an oscilloscope to observe these of signals. There are some inexpensive add-on oscilloscopes for laptop PCs. If you don't have access to an oscilloscope, testing on the DC scale of a voltmeter isn't accurate but you may see some needle twitch. When testing the sensor with a voltmeter it is best to use an analog AC Volt gauge. Set it at the AC 20V scale to begin with and then decrease the scale if necessary to see voltage information.
Crank the engine and note the voltage reading. The minimum output of an inductive engine speed sensor is 3V (AC) when cranking the engine. Some non-Porsche ECU-s need much more (20V) to recognize the inductive signal. If a test is performed when engine is running or somehow cranking at higher speeds switch it to the 200V scale. An inductive sensor can output a total voltage of 120 Volts when triggered at high rpm. Be careful, these are high voltages!
If the minimum voltage output is not obtained, the speed sensor should be replaced.
Place the connector back onto the spark module
Disconnect the LH connector
Test for spark module output
IF the engine speed sensor tests OK, the next test is to determine of the spark module is outputting a speed signal to the LH module for RPM information. The spark module output voltage is measured at LH pin 1 for all 928 LH module types. Crank the engine and note the voltage reading. This signal must be at least 7V, alternating between 0 and 7V in a square wave proportional to engine RPM. Voltmeters may have trouble providing accurate readings with square waves, so an oscilloscope is needed for an accurate test.
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dzaprev (11-21-2019)
11-24-2004, 03:11 PM
#3
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Article with wave traces
I completed a PDF document that summarizes testing the inductive RPM speed sensor and the spark module to LH communication. If you'd like a copy, drop me a line at info@electronikrepair.com
05-30-2016, 11:53 AM
#4
Race Car
O'scope signal Cps readings
86 S/C
Having random no start when hot Temp II looks good but with a scope on the Cps I am seeing a consistent spike above the base line. Looking for anyone that has tested this with a scope and what they were observing.
Thanks
Having random no start when hot Temp II looks good but with a scope on the Cps I am seeing a consistent spike above the base line. Looking for anyone that has tested this with a scope and what they were observing.
Thanks
11-13-2019, 12:19 PM
#5
Good afternoon here in Spain, I just read this thread and I have several doubts the voltage output signal of the cps sensor is measured on pin 23 of the already negative EZK connector, I am not getting any reading, female connector of the rebuilt harness and well connected, white to pin 1, black pin 2 and armor pin 3, the problem I have observed is that in one day for the car to start I have to insist more than usual until the fuel rail takes pressure, new relays except that of the ezk, pump fuse, pump, filter, etc., all new, once it has started there is no problem, the problem of starting is when the fuel pressure in the rail drops, otherwise the perfect car , I have tried with two cps with the same result, any solution? Thank you very much for this great forum, it is impressive.
