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
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.
'79 Euro-hybrid 5-liter track beast
You've been focusing on fuel injection issues. It may be that you have a spark related problem. I’ll focus on those issues in this post.
You're flying in the dark without an oscilloscope. There are several signals to check that could help you find the problem and a volt meter isn't the correct tool. If there is a local shop that has the proper tools and system knowledge, they could help - even if they aren't experienced with the 928. My website provides the information that they are lacking. What we don't know is if the engine stalls due to lack of fuel or spark going weak.
Key items to check in the ignition are:
a. Inspect and test the connection to the engine pulse sender (called RPM sender in the schematics) and replace if necessary. If the signal voltage is too low, isn’t "clean" or if it drops off when things heat up the spark and fuel system will shut down. I've had several other 928 customers that chased down a lot of issues and found they had a bad pulse sender. The part number is 944.606.115.00. The EZK connector to pulse sender connections are:
- pin 23 to speed sender (+)
- pin 6 speed sender negative (-)
- pin 24 speed sender shield.
The test that you can perform is a resistance test. It is best to start the measurements at the EZK spark control module connector, since the test verifies the complete circuit. You will need to fabricate a test lead to with a blade to plug into the connector. The resistance reading should be between 600 - 1600 Ohms at EZK connector pins 23 (+) and 6 (-). If the test doesn’t yield the desired results, disconnect the engine speed sensor plug to the wiring harness, clean the connections and test at that point.
An oscilloscope is really needed to test further. Since a shop with the proper tools will probably charge an hour or more of labor, replacing the sender will cost the same or less than testing it!
b. Inspect and test the connections and from the EZK spark controller to the spark final stage (called "ignition trigger unit" in the schematics, "ignition switch unit" p/n 928.602.706.01 in PET and either “switch gear”
or “control unit” on the LH connector diagram). The control units are located in the black box ahead of the radiator with the plastic cover.
The EZK connector to control unit (called control unit 1 and 2 on the EZK connector diagram) are:
- EZK connector pin 32 to control unit 1 (left) pin 5
- EZK connector pin 15 to control unit 2 (right) pin 5
The control unit pin-out and EZK connector pin-out are provided on my webpage www.electronikrepair.com diagnostic page and EZK page.
c. Inspect and test the connections from the control unit pin 1 to the ignition coils pin 1.
d. Inspect and test the ignition coils
e. Inspect and test the coil to distributor wire, and distributor to spark plug wires (including resistance).
If the connections from the EZK to the control units aren't clean or the control unit to the coil connections aren't clean you will have spark problems. There is information regarding coil testing and spark plug wire resistance checks in past Rennlist posts or on Greg Nichol's website.
It is also possible that your engine is flooded out. Remove all the spark plugs, crank the engine, and let the car sit overnight before installing spark plugs so un-burnt fuel can evaporate from the cylinders.
I hope this information helps.
'79 Euro track beast