Lorenfb

"Can anyone with a working (e.g. no SAI fault) car report the voltages seen during air injection pump operation on the before TWC and after TWC sensors?"

If one has access to the Porsche testers (PST2/PIWIS), it's easy to run the
SAI test and watch the O2 voltage as it changes. I've done that many times for
many shops in preparation for an emissions test. Both the SAI and Tank
Venting tests can be done in less than 2 - 3 minutes using either tester.

If one has a good relationship with a Porsche shop, you can ask them to use
their Porsche tester and run the SAI test. If your good SoCal Porsche shop
lacks the tester, have them call and I'll do the test at their shop. That will
determine immediately whether the SAI test will pass.

User 122821

I have one '96 993 with no SAI problems (clean ports). I will get a reading on that car with a Vag-Com this weekend which will show voltages at the ECU.

I'm starting to believe the '97 and '98 have a different algorithm for the SAI verification than the '96. I can see a slight voltage might be better than zero as the circuit works now.

Lorenfb

"I will get a reading on that car with a Vag-Com this weekend which will show voltages at the ECU."

Right, but it won't tell you whether the DME ECM accepted the voltages
and passed the SAI test. Remember, the way the 993 OBDII monitor
system functions is that all the monitor tests must complete before any
tests will be indicated when reading the monitor tests via an OBDII
scanner.

User 122821

Since the car has all the registers set, completely stock, and does NOT have have the bypass circuit, I would say the ECU is accepting all the values.

I have two '96 993s. One has the SAI issue and the other does not.

earossi

For those of you who are starting to lose faith that the latest SAI test circuit is not the solution, please keep the faith. What you are witnessing on this wonderful forum is some honest R&D effort ("research and development") working towards a solution. To me, it is obvious that we have a hand full of RL folks who have the knowledge and truly "get it" when it comes to identifying the problem and then collaborating on a proper solution.

While it appears that Flying Low's circuit used in one of his cars does work, it may not work in all of the 993 models out there. It has become apparent to others that the logic programmed into the ECU's for our cars may differ year to year. The recent postings show that this has been recognized and possible solutions have been suggested, along with the need for further testing. Being an engineer by trade (though not an electronics engineer), the process is music to my ears. I am confident and enheartened that, together, this group of folks will collaborate leading to a better understanding of the challenge and then determining a best fit solution for the newly defined issues.

Personnally, I will hold off installing the circuit in my car until our scientific group reaches some conclusions and makes some recommendations. So, keep the faith.......what you are seeing here would cost a small fortune to orchestrate in a private company. And, we are getting the benefit of the effort simply because we share a common bond which is the love for these German machines!

2ndof2

+1 on earossi's comment and I suspect the rest of us who are electrically challenged feel the same. Never lost faith in this...just looking for the results to date. Thanks to those doing the R&D...

911Dave

Personally, I don't understand the skepticism. The possiblity that it might not work on 97-98 cars has only been suggested by posters with no real data or knowledge to back it up. I'm not going to start doubting until I have a bona fide reason to. Besides, what possible reason could Porsche engineers have to change the voltage characteristics of an OBDII monitor signal from such an obscure, non-critical system that worked perfectly well in '96 models? That would have been a complete waste of time and resources.

Lorenfb

"Besides, what possible reason could Porsche engineers have to change the voltage characteristics of an OBDII monitor signal from such an obscure, non-critical system that worked perfectly well in '96 models?"

The OBDII spec may have required that the O2 signal actually begin
to change as the injected air reached them, e.g. to possibly prevent
a SAI work-around. Also, just like when Porsche implemented the early
993 ('96) and read more into the ODBII spec than did domestic (USA)
car EOMs did, e.g. All the monitors (readiness codes) must complete
before any appear to an OBDII scan on the 993. For the 996, the monitors
showup as they are completed. And then for the later 993 (97/98),
the tests complete faster. M/B had the same methodology/approach
as Porsche in those years for OBDII monitors.

ltc

Interesting to note that this subject (and circuit) was discussed here on RL back in 2006

https://rennlist.com/forums/993-foru...s-circuit.html

and this one from back in 2003

https://rennlist.com/forums/993-foru...-build-up.html


I had no idea....came across it by chance.

rbettenhauser

Would any body have a recommendation on a good machine shop near the San Clemente, CA area? I am "all in" on the circuit but my ports are totally clogged and inspection time is comming up. I unfortunately fall into the 1997 993 voltage challenge bucket :-)

air993

I installed my tester in my 97 and the check engine light appeared after the drive cycle was completed. Code 1123 came up. Which I think is either o2 sensors, vaccum leak, and/or MAF sensor. Maybe someone can verify that this is not SAI related. My car does hesitate a little sometimes so I'm thinking MAF sensor. Anyway ordered a new sensor from autohaus... Will update as I know something.

Lucas

User 122821

There is a thread on this code.
https://rennlist.com/forums/996-foru...de-1123-a.html

P1123 - Oxygen Sensing Adaptation Area 1 (Cylinders 1 - 3) - Lean Threshold

Fuel/air mixture is so rich that sensing is up to its lean threshold.
Most likely causes:
Fuel pressure too high.
Fuel injector leaking.
EVAP canister purge valve open.

This circuit will only help with issues P1411 & P0410‎. It seems you might have a different issue to track down.

Lorenfb

"I have one '96 993 with no SAI problems (clean ports). I will get a reading on that car with a Vag-Com this weekend which will show voltages at the ECU."

And the numbers were?

User 122821

Readings on a stock '96 993 with clean SAI ports are

.46 - .48mV without the SAI pump running
.13 - .09mV with the SAI pump running

User 122821

Kind of impatient considering you probably already know the numbers considering your line of work