It doesn't matter! Look at the scope image again, it indicates the correct FV signal;

http://forums.pelicanparts.com/uploa...1592581597.jpg

Yes, but ... this is „my“ output from my oscilloscope you’re quoting, I got the same model[emoji846]

Look at his one more above


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Sorry. Yes, he has a hookup problem, or bad battery. At least his DC is correct. He needs to measure the voltage
on pin 8 with the scope. It should be 12V. Then disconnect the ECU and measure pin 15 with the key "on".

http://forums.pelicanparts.com/uploa...1592173638.JPG

6.56V in your pic about the same as mine. Is this an example of a bad one?

Also measured across the FV connector with FP relay jumpered got 9.8 VDC. Is that an acceptable voltage drop?Should be 12VDC?

Battery is new and measures 12-13 volts and on a tender.

Used DVM ECU unplugged key on, pin 8 12.3V pin15 11.8V.

My Bentley does not show a pin 8 on the diagram but does have 2 pin 15 one is blk/wht the other blk/red to the OXS relay. The black/white 15 in the Bentley should be pin 8?
http://forums.pelicanparts.com/uploa...1592841594.jpg

How do I test the test port itself? Pin 17 shows continuity but are there other things to look at such as the the brown and red wires? Sometimes I think all my things are working as they should but the test port itself is not transmitting the info accurately.

No, the 6.56V is the average voltage; DC X battery voltage = 50% X 13 volts = 6.5 volts

Yes, and about 13V with the engine running.

I can hear and feel my FV running. Would the lower voltage result in a weak FV or one that was not accurate? Should I look for a grounded/broken wire?

Thanks

Pin 8 and one pin on the FV should have the exact same voltage (12V), not the FV pin that goes to pin 15.

Focus on using your scope to determine how the control pins (2/7/12) affect the DC!

Measured 9.7 V across the FV plug sockets.

Measured 12.3 V from one socket and other probe grounded to engine (same as pin 8)

The easiest way is to disconnect the ECU connector, start the engine, and measure between pins 15 and 16.
You should measure at least 12V.

With the FP relay jumpered and key on, 15 to 16 is 12.6 VDC

Good! Again, determine whether the control inputs (2,7,12) affect the DC. If not, you have a bad ECU!

Last time I measured the voltage output on pin 15 of the ECU together with a test light. Below a recap of the measurements. Probably I have a bad ECU, but it was advised also to measure it with an oscilloscope to check the duty cycle. These are the oscilloscope results (connected with 6V out adapter) with a non running engine:

https://ibb.co/FDCJcjc
https://ibb.co/82QRvwk
https://ibb.co/2yfPDyh

Same results if I connect the CUAE.

What do you guys think?? Do I need to replace the ECU by a new one?


=====
RECAP:

The voltage input to the ECU was 11,8V by bridging a wire from pin 30 to 87a, before I started doing the tests:

1. I disconnected pin 2, 7, 12 and the AEC => Pin 15 shows a weak light and I measured 0.88V
2. I disconnected pin 2, 12 and the AEC. Pin 7 grounded and/or WOT => Pin 15 shows a slightly brighter light and I measure 1,0V.
3. I disconnected pin 7, 12 and the AEC. Pin 2 grounded => Pin 15 shows a slightly brighter light (than step 1) and I measure 1,22V
4. I disconnected pin 12 and the AEC. Pin 2 and pin 7 both grounded => I measure 1,0V on pin 15.
5. I disconnected pin 7, 12 and the AEC. Pin 2 connected to a small 1.5V battery => I measure 0,60V on pin 15

Your ECU is functioning as it should. Now connect all inputs except the O2 (pin 2) and re-test.


Incorrect test procedure!

I also did that measurements off course:
Pin 2 disconnected, CUAE connected, pin 7 and 12 connected (oil temperature is around 20 degree Celcius by the way) => 50.8% dutycycle
Pin 2 disconnected, CUAE connected, pin 12 connected, pin 7 grounded and/or WOT => 35.5%

Why is that an incorrect test procedure? On measurement number #1 I should expect 6V and not 0.88V with 50% dutycycle. Numbers #2 to 5 also different voltage taking into account the dutycycles. When I drive my 911 I hear the FV buzzing very very frequently (high tone), so I assume it is not working properly because the ECU doesn't change the voltage on pin 15 correctly.

I am lost again....

I am able to get a new ECU, but will not spend the high amount of money if not needed

As I said, your ECU is OK. Your scope images prove that. Hook everything up and set the mixture for 50% DC when the engine is warm.
When idling, pins 7 & 12 should be at 12V using a good voltmeter. Then ground pin 2 and the idle will decrease indicating the mixture is getting rich.

A test light is used to simulate (one lead on 12V and the other on pin 15) the FV, when the FV is disconnected.

Hook up everything to check the 50% dutycycle will be step 4 than? The Porsche specialist already executed step 1,2 and 3 as shown on the inside of my engine cover lid. The Co measured is 0.8 so that’s already in spec.

http://forums.pelicanparts.com/uploa...1593073008.jpg

This is about a 2.5-3 volt drop at the FV. Is this ok? If I ground to the cam cover
it shows over 12V. Why the difference?

Thanks

depends on the duty cycle via Ground wire provided by the ECU which makes the volatage dropping.
if leading the ground pin of the FV to ground instead to the ECU and 12v result, then the voltage at the FV from the oxs relay is ok.

Finally had some time to take another stab at this today.
With FP relay jumpered, key on and everything plugged in, grounded pin 2,7 and 12.
Btw anyone that wants to do this it is much easier with the seat removed as shown.

Instead of connecting the scope to the test port in the engine compartment I used black probe to pin 17 as shown here and grounded red probe to the frame. A bit confusing as I should have switched the extension wire colors to match but I did not think of it. Per Bentley pin 17 is the test port wire.

To ground each pin I used Pin 16 which is a brown wire ground at the lambda ecu. You can see this in a couple of the pics below.

http://forums.pelicanparts.com/uploa...1593363212.jpg

Pin 2 grounded to pin 16 after about 15 seconds it drove up to 93%:

http://forums.pelicanparts.com/uploa...1593363784.jpg

Pin 7 grounded at pin16 is 64%:
http://forums.pelicanparts.com/uploa...1593363461.jpg

Pin 12 grounded to 16 is 74%:
http://forums.pelicanparts.com/uploa...1593364012.jpg

Is everything working well enough to set the mixture to 45%?

Thanks

Hopefully, you are aware that, since the O2 sensor lacks a heater, the engine must be warm and the RPM should be about
1500-2000 to set the mixture. Once set, the DC should vary slightly around 45%, and the O2 voltage will vary about +/- .20 volts.

Why does the rpm have to be 1500-2000 instead of around 1000 (idle)? Is that just to make sure the O2 sensor is warm enough to generate voltage?

Thanks

That's correct! Once fully warm, e.g. after driving for 30-40 minutes, it'll provide a good signal at idle.
For some O2 sensors, though, that might not be the case. That problem was eliminated on the later
Porsches by adding a heater.

I figured out that if the base CO setting is set at 0.4-0.8% (factory default), then the idle duty cycle on a warm engine jumps around 60%.
And thats normal as the 0.4-0.8% are leaner than lambda 1 and after the ECU regulates the mixture back to stoich/Lambda1 a typical CO of approx. 1.5% is the result (before cat!).

Many people (like myself) do suggest setting the CO screw so a 45% duty cycle at warm idle. But this also sets the cold start and WOT enrichment out of spec and in fall/winter in cold regions like the NE or in Germany the cold start for example will result far to rich.

Finally got it.
 

Finally, after at least three months trying, I was able to accurately measure and set my FV today to a duty cycle of 45% and measure my O2 sensor output at .52 VDC at the same time. I was never able to do it with a DVM. AndrewCologne, Dave at mysocal911 and the guy at Systems Consulting whose name I cannot recall (sorry!) patiently lead me through the long process until it all came together. I believe it was Dave who mentioned that the FV itself can sometimes interfere with the DVM reading and this ultimately was the key to getting it done.

It’s really not hard to do with an oscilloscope, but who has one of those?? I do. $42 bought a cheap one on Amazon (see pics above), and surprisingly it worked great.

Just to make it easier for anyone looking at this in the future, I’m going to submit a separate post on how to use the scope. I was a bit intimidated by the thing but it really is a cool instrument. Now that I have an accurate, repeatable way to measure my mixture I can move forward with other projects.

And finally, an apology to wosm for sort of hijacking his thread.

Thanks again everyone!http://forums.pelicanparts.com/support/smileys/clap.gifhttp://forums.pelicanparts.com/support/smileys/clap.gif

@Funracer, great you solved your issue! Beside Dave and Andrew, you also contributed to this topic , so lots of thanks too :)

I had some busy days at work and was not able to drive my 911 sc until today. I measured pins 7 and 12 both during idling and the Voltmeter showed me ~12V. After driving for more than half an hour I used my oscilloscope again. Results on dutycycle were exactly the same with engine running (50.6 % with pin 2 disconnected; 35.7% with pin 2 disconnected and pin 7 grounded; 26% pin 12 grounded to pin 16). My Co is 0.8 without cat. So I think my ECU functions also OK. However, it is still very strange that nothing changes with idling when I remove my relais under the passenger seat or ground pin 2. It stays one big puzzle for me :(

I still don’t know what is causing my engine runs that bad when cold and hesitates around 2000 rpm. No vaccum leaks, ignition timing re-set according specs, fuel pressures OK, etc. When the engine is warm the hesitation/stutter is less at 2000. The car doesnt hesitate when I give more throttle. I think I need to inspect my plugs or use others to test any difference. Also I have some doubts on algae in my tank and/or fuelfilter causing this misery.

Would mean you connected your DMM the wrong way as 35% should be 65%, means inverse. This will be achieved by a proper inverse conneotion of the DMM's terminals when reading duty cycles where the ground signal gets interrupted by the duty cycles pulse modulation.