quinto555

Rich,

I just had done my homework, and the results are following:

When touching a 12 volt source on the White line (left ignition circuit) = HAS SPARK!
When touching a 12 volt source on the Green line (right ignition circuit) = HAS SPARK!

Then I reconnect the two-pin plug and test crank the engine, this time NO SPARK .
Then I bridge the EZF Control Relay and the LH Jetronic Relay and also NO SPARK.

So, after these tests, I can be sure that both COILS and both IGNITION UNIT (Transistors) are in good condition.

Now the only suspect is the EZF Control Module and maybe…… the Engine Speed Sensor…. Because two days ago in your post “TESTING THE 928 ENGINE SPEED SENSOR” you wrote “The minimum output of an inductive engine speed sensor is 3V (AC) when cranking the engine”. This is quite different with what you toll me before, that the minimum is 1.4V (AC) . Please clear me up this matter.

Roberto

Rich9928p

Congratulations! You have a good first step. We know the coils and final stage circuits are good.

Regarding the inductive speed sensor, Porsche's documentation provides two different values measured with an oscilloscope, 2.5 V in the original LH section (which is for your 928 type) and 3V in the S4 update (the 1.4V was my memory error). Also, there is a voltage spike of several volts at the Reference Mark point that a voltmeter will not display. Voltmeters are not designed to respond accurately to these types of signals, so any movement on the A/C scale indicates you are getting a signal from the sensor. You really need to use an oscilloscope to get an accurate reading of what is going on! Based upon your 2V voltmeter observation, I tend to believe that your inductive sensor is working, we just don't know how well. Did you try the Ohm test and the test the shielding? If those checks are positive then you could feel even better about the sensor.

If you have a laptop computer, the cost of an oscilloscope "add on" is pretty low. If you save the money from buying parts that are not needed you will have paid for the oscilloscope many times. Just do a “google” search on USB oscilloscope.

I would focus on the wiring to the EZF unit. The fact that bridging the EZF and LH do not start the system gives us additional information.

As I recall, you confirmed that you have battery voltage at position 30 of both relays. When you bridge the LH and EZF relay pins 30 and 87, you perform the same function as the relay "turning on" the system.

So the next test is to check the circuit from relay connector position 87 to the EZF module; measure the resistance from EZF Relay VIII pin 87 to EZF connector plug pin 25. The resistance should be close to zero Ohms. As a second check, next bridge relay VIII and check for battery voltage at EZF connector pin plug 25.

Next, test the resistance of the circuit from EZF connector pins 1 and 13 (ignition pulse) to ignition control (switchgear) I and II connectors at their pins 5.

Ground circuits are very important too, systems will not run with a bad ground connection. You need to check the resistance between EZF connector pins 10 and 12 and a good chassis ground point. The resistance should be close to zero.

If these tests all show no problems, then the odds are high that either the EZF module or the RPM speed sensor are the problem with your 928.

quinto555

Rich,

I’m happy to see fewer sparks after more than 3 year of waiting, even though this is almost hand-made.

One of the problems we have here is that Oscilloscope is not available locally and if available they will cost 3 to 5 time more than imported from the US, so most of my tools and instruments are imported from your country but the drawback is time consuming, in the US you can have your order in 1-5 days but I have to waiting 2-3 months instead. I have call several friends buy none of them has oscilloscope; the only other possibility is to find a TV repair men to bring his oscilloscope here but with a price.

I already searched for the USB Oscilloscope but most of them are informal and unknown maker, also their price are not much different comparing with the desktop entry level oscilloscope as this one by B+K Precision http://www.testequipmentdepot.com/b+...sion/2120b.htm, which has special price of $339.00, do you think it is a good buy?

Later today I will take off the Speed Sensor to check the shielding resistance and other connection you indicated.

Roberto

T_MaX

I have no first hand knowledge on this item, but I have read a few reviews on it and for the price, it seems to be a nice tool.

http://www.picotech.com/oscilloscope.html

Rich9928p

Roberto,

The B+K Precision scope looks just fine, it is actually more then you need. If you could find a used scope locally that would be fine too. If you'll never use the scope again, it may be worth paying the TV guy to make a Porsche call!

Good luck,
Rich

quinto555

OK Rich, here is the last test report:

SPEED SENSOR
Pin 7 to Shielding = 0.6 ohm.
Pin 19 to Shielding = 1.068 k-ohms.
Pin 26 to Shielding = Infinite ohm.
Pin 7 to 19 = 1.068 k-ohms.
Pin 7 to 26 = Infinite ohm.
Pin 19 to 26 = Infinite ohm.

RELAY TO EZF
Relay VIII pin 87 to connector plug pin 25 = 0.8 ohm.
Bridge relay VIII to connector plug pin 25 = 13.46 VDC.

RESISTANCE
EZF connector pin 1 to Ignition Control plug I pin 5 = 0.2 ohm.
EZF connector pin 13 to Ignition Control plug II pin 5 = 0.2 ohm.
EZF connector pin 12 to ground = 0.4 ohm.
EZF connector pin 10 to ground = Infinite ohm. ** Here I think has an error, because according the circuit diagram (page 97-193) the pin 10 is connected to the Intake Air Temperature Sensor and return to the pin 22, no ground I can see in between, but between pin 10 to 22 has 2.271 k-ohms.

Roberto

quinto555

T_MaX,

Definitively it is a very sophisticate oscilloscope, but for a beginner like me I would like to learn to use this with a simple and cheaper basic oscilloscope, the less expensive of the PicoScope 3000 series is price at $695 and still need a notebook with USB 2.0 to go with.

quinto555

Rich,

I will order this B+K scope, but it wouldn’t arrive here until January or February, meanwhile I will call few TV guy and see if one of them will come, it maybe the only way to go.

Now I have the Speed Sensor out on my desktop, are there any other tests I can do before return it where belong?

Rich9928p

SPEED SENSOR
Pin 7 to Shielding = 0.6 ohm. what do you mean by Shielding?
Pin 19 to Shielding = 1.068 k-ohms. ?
Pin 26 to Shielding = Infinite ohm. ?
Pin 7 to 19 = 1.068 k-ohms. OK
Pin 7 to 26 = Infinite ohm. OK
Pin 19 to 26 = Infinite ohm. OK

RELAY TO EZF
Relay VIII pin 87 to connector plug pin 25 = 0.8 ohm. OK

Bridge relay VIII to connector plug pin 25 = 13.46 VDC. OK

RESISTANCE
EZF connector pin 1 to Ignition Control plug I pin 5 = 0.2 ohm. OK
EZF connector pin 13 to Ignition Control plug II pin 5 = 0.2 ohm. OK
EZF connector pin 12 to ground = 0.4 ohm. OK
EZF connector pin 10 to ground = Infinite ohm. ** Here I think has an error, because according the circuit diagram (page 97-193) the pin 10 is connected to the Intake Air Temperature Sensor and return to the pin 22, no ground I can see in between, but between pin 10 to 22 has 2.271 k-ohms. This was my error, you don't need to measure this signal, it is an internal ground of the EZF module.

The test shows your speed sensor resistance is withing spec. So it is likely OK. The EZF is gettting voltage and the ground is good. Things point to the EZF module not working.

Rich9928p

Roberto, you have done all that you can do with the sensor.

quinto555

I mean the cup style metal shell on witch hold the small coil inside.

ErnestSw

Would it not be faster and cheaper to just replace the sensor and send the EZK module for testing? You would save the $$ for the scope and you can get the sensor from one of the big three sent to you by registered mail. The sensor for my GT was about $100.00 if I remember correctly.

quinto555

ErnestSw,

My 928 is not in the US, It would cost lots of money to send the modules to the US and when send it back, this country custom will charge me tax as a new unit, that is why I need to be sure that this unit need to be repair and not just testing.

quinto555

Rich,

Around February this year, I sent this EZF together with the LH module to one of the Porsche dealer in LA to check both units, and the result was that the EZF is the good one and the LH is the bad one, so they sell me a rebuild LH Jetronic (of which I ignore if it is good neither).

Now that all the fingers are pointing to the EZF module, I wand to know how to test this module to make sure that he is really the bad guy?

Rich9928p

The easiest way is to plug in another EZF module and see if your 928 starts. How to test the EZF? That is a trade secret.