High dwell on 911 SC ‘81 lambda (US)

[mysocal911]

Originally Posted by AndrewCologne

Hi Dave,

yes, average of 6.3V at 50% Duty Cycle .... but i do refer to his output.

Mine provides full 12.98V as Vmax to the FV when PWM is high, ... but his output is max 6.69V (in his plot its minus, as he connected it reverse) so he gots an average at 50% of 3.24V ...

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

[AndrewCologne]

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

Look at his one more above


Sent from my iPhone using Tapatalk

[mysocal911]

Originally Posted by AndrewCologne

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

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".

[Funracer]

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?

[Funracer]

Originally Posted by mysocal911

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".

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?


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.

[mysocal911]

Originally Posted by Funracer

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

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

Originally Posted by Funracer

Also measured across the FV connector with FP relay jumpered got 9.8 VDC. Should be 12VDC?

Yes, and about 13V with the engine running.

[Funracer]

Originally Posted by mysocal911

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

[mysocal911]

Originally Posted by Funracer

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!

[Funracer]

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)

[mysocal911]

Originally Posted by Funracer

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.

[Funracer]

Originally Posted by mysocal911

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

[mysocal911]

Originally Posted by Funracer

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!

[wosm]

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

[mysocal911]

Originally Posted by wosm

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

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

Originally Posted by wosm

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

Incorrect test procedure!

[wosm]

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

[mysocal911]

Originally Posted by wosm

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%

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.

Originally Posted by wosm

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.

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

[wosm]

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.

[Funracer]

Originally Posted by Funracer

Measured 9.7 V across the FV plug sockets.

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

[AndrewCologne]

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.

[Funracer]

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.



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



Pin 7 grounded at pin16 is 64%:


Pin 12 grounded to 16 is 74%:


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

Thanks