Need recommendation for Oxygen Sensor Control Unit repair service

[ManniB]

Although I received a lot of help to checkout my CIS problems I didn't find a solution. As it looks, my Oxygen Sensor Control Unit is bad and needs to be repaired ('80 SC US model).

Thus, I need your recommendations for a repair service. Do you have any experience with the service of a certain company?

Thus far, I have found Specialized ECU Repair on the internet. Any experience with them?

Thank you, Manfred

[Lorenfb]

"As it looks, my Oxygen Sensor Control Unit is bad and needs to be repaired ('80 SC US model)."

Those ECUs are very reliable and rarely fail with the exception of water damage.
Most mis-diagnose the Lambda system and assume it's the ECU.

[lonewolf]

Loren knows.
Mann.I think your going way too far.
Loren you need to read his other thread .

[ManniB]

Loren & Lonewolf,
I very much appreciate your doubts and I understand that you want to save me from making a costly repair that turns out to be unnecessary.
However, I have tested everything in the CIS system for days, all fuel components, the ignition and all signals and power supply at the control unit. If all turns out to be OK the only conclusion for me is that the control unit itself is the problem.

Take for example the fact that the duty cycle for the FV is at 15% when cold (15C switch closed). The control unit ignores all other inputs in this mode of operation and should emit an 85% duty cycle for enrichment. I would be glad if anyone could give me an explanation and point me to what I should check in addition.

Thank you, Manfred

[lonewolf]

Manni.
Your only problem(if a problem) is being rich on startup correct?
you say car runs fine once warmed up. if the car runs fine when warm then your ECU and the rest of it has to be ok.
The symptoms you describe tell me that it is too rich on startup.
it chugs,black smoke and hunting all signs of being rich but once warm you says it's ok.
If that is correct I don't see a big problem. Have you tried adjusting the fuel distributor?
I don't know if it's because it's a porsche but too many people here think that their problem is caused by some hard to find ,mysterious electrical gremlin that only a porsche has.
It's just a car with an engine ,fuel and ign system.try to look at it logically.
I mean no offence but this is your first 911 and you just bought it .Like I said earlier go slow.
I've been driving a 911 for 30+ years now and learned not to jump to conclusions.

[ManniB]

Originally Posted by lonewolf

Manni.
Your only problem(if a problem) is being rich on startup correct?
you say car runs fine once warmed up. if the car runs fine when warm then your ECU and the rest of it has to be ok.
The symptoms you describe tell me that it is too rich on startup.
it chugs,black smoke and hunting all signs of being rich but once warm you says it's ok.
If that is correct I don't see a big problem. Have you tried adjusting the fuel distributor?
I don't know if it's because it's a porsche but too many people here think that their problem is caused by some hard to find ,mysterious electrical gremlin that only a porsche has.
It's just a car with an engine ,fuel and ign system.try to look at it logically.
I mean no offence but this is your first 911 and you just bought it .Like I said earlier go slow.
I've been driving a 911 for 30+ years now and learned not to jump to conclusions.

Lonewolf,
I think its a good idea to keep the technical discussion in the other thread so others can follow more easily. Ive posted and aswer over there.
Other thread
Thanks, Manfred

[Lorenfb]

Most are unaware of what the Lambda ECU's function is!

1. It enriches for cold start (makes easier) based on the oil temp switch.
2. It provides for accel enrichment.
3. It maintains an AFR (Lambda = 1.0) based on the O2 sensor input.

And THAT's it!

The Lambda ECU can be disconnected and the engine will run normally
once the mixture screw is adjusted, but it will have a harder cold start
and poor accel under load, and of course no O2 control. So, if the engine
won't run properly with the Lambda ECU disconnected, then it's NOT the
problem.

Again, diagnosing the Lambda system is very simple!

[Lorenfb]

And now on the issue of duty cycle (DC).

The proper way to define DC is relative to the percent time the FV is grounded.
Then when the temp switch is grounded (cold), the DC will be about 85%, i.e. the FV
is at ground about 85% of the time. One can also define the DC as 15%
relative to the FV being NOT activated (grounded). The key point is that the mixture
is being enriched 85% of the time versus the normal of 50%. The DC for enrichment
is also increased, besides pin 7 (oil temp), by grounding pins 11 & 12 (on some ECUs)
the accel enrichment pins. Note: A grounded O2 sensor will result in a DC > 85%.

Actual tests (Bosch 0 280 800 037) for FV period of 15ms:

1. Pin 7 grounded - T (off) = 5.4ms, DC = ( 15 - 5.4 )/15 = 64%
2. Pin 11 or O2 grounded - T (off) = 1ms, DC ~ = 93%
3. Pin 12 grounded - T (off) = 3.8ms, DC = 75%

Check for additional Bosch Lambda ECU part numbers: http://www.systemsc.com/Parts.htm

Bottom line: Grounding the FV enriches the mixture with varying DCs.

Note: Avoid this thread for mis-information: Please help diagnosing '80 SC CIS (idle) problem