ltc

In the end, 94 boards/kits were shipped.
I do not know which members owned what model year.

It would seem that you question any RL member who reports that the board addressed their issue, yet you can not look at the design and state why it should or should not work, even with your commercial knowledge and expertise with Porsche ECU's.
Again, if you have any design inputs, I would be glad to implement the design.

Lorenfb

"It would seem that you question any RL member who reports that the board addressed their issue,"

Not really. It would be great if others can come forward to provide more feedback.
As of now, there's one late 993 where there's positive results and one with
negative results.

"yet you can not look at the design and state why it should or should not work"

There's nothing wrong with the design nor the implementation. It's just
possible that some wrong assumptions were made about the late 993.
At this time, not having access to a late 993, I don't know what the problem
(if there is one) may be. That's why more late 993 purchasers need to provide
feedback.

william_b_noble

what we do know from the two reports with respect to later cars, mine and the C4S, is the following:
1. the C4s owner cleared the CEL, and I am suspicious that the car has not satisfied the cycle flag, the flags will not set in one drive cycle no matter what. The C4s reports success
2. the C2 (me) did NOT reset the CEL. In the past, when I've cleared the passages using solvents and air, the CEL clears itself on the second drive cycle after the repair. This did not happen using the circuit. I just checked and my car (according to the Garmin unit, not cross checked with my OBDII reader) says it has a P0410 (SAI fault) and a P0411 (unknown) code. I suspect I have much higher mileage (150K) than the C4S but that should not matter.

Note that I did verify that the circult as installed in my car was working - all four sensors read zero volts per my OBDII reader during the SAI pump run time, so I didn't mess up the connection or the circuit - and the car idled worse when the circuit was active than when it was not active - that says something too.

Lorenfb

A possible solution, if the problem is a minimum O2 voltage, is to connect both front FET
sources to a voltage reference of 10 - 20 millivolts. This is easily made using a 10K ohm
& a 10 ohm resistors in series. The 10K is connected to the input voltage and the 10 ohm
resistor to ground with the junction of the resistors connected to the FET sources. This will
provide a little more than 10 millivolts when the FETs turn on which prevents the O2 sensors'
voltage reaching less than a potential minimum. If that voltage is still too low, the 10K can be
reduced to 6.8K resulting in about 20 mv.

william_b_noble

the real question is, "is the problem a minum non zero O2 voltage" or is it something else? Is there a third person who has tried this with a 97 or 98? I suppose I can hook the circuit as is back up and see what happens or add a resistor divider as loren suggests, or for more stable voltage, use a resistor divider across a silicon diode (series of 10K and forward biased diode to form .7V ref, and then a divider across the .7 - 100 ohms to ground, in series with 20K to the + side of the diode will give about 20 mv with ore stability). But I wonder, can the computer really distinguish 20 mv from zero given the noise pickup in the wires? This just doesn't seem right...

Lorenfb

"But I wonder, can the computer really distinguish 20 mv from zero given the noise pickup in the wires?"

So without doing any testing & analysis one can continue to guess and hypothesize.

"for more stable voltage, use a resistor divider across a silicon diode"

Not really. The diode voltage will vary from .50 volts to .90 volts over
an engine compartment temp change. Besides, the closer the source
voltage gets to desired voltage the greater will be the effect of changes
on the desired voltage, e.g. 13V & 12 mv ~ 1000:1, so 14V results
in 1 mv change. Using a diode results in; 750 mv & 12 mv ~ 60:1,
or for +/- 200mv over temp the change is +/- 3mv.

william_b_noble

I guess the best thing is to just make the resistor divider and see what happens, but it would sure be nice to know what is really needed. I think you are right that the diode won't add much to the circuit and in fact might detract. If I have some spare time and energy this weekend I'll see if I can try adding the divider. But with my OBD tester, I can't really watch the SAI test in any detail so I can't tell if I'm doing good or not other than to let several drive cycles pass and see if the CEL goes off.

Lorenfb

"I'll see if I can try adding the divider."

You might also try a 5K ohm versus the 10K. This will give about 20 mv.
Doing this test should eliminate a minimum voltage as being the issue.

craig001

Has Round 2 of these puppies still be openor made by someone here? Is so, can I get on the list with enclosure. Do not mind paying in advance. I just failed my emissions - low volts pre and after on my 96.

C4S993

How do you know the pre and after 02 sensors failed and which side ?
Vertex sells them (BOSCH w/ correct connectors) for tad over $100 each. (1996 172k mile C4S) just replaced the two right side 02 sensors and still failed (error 1123) so now I have to change the left side 02 sensors. If that still fails i will change that vapor canister. Have already changed all 12 plugs with lower #6 plug taking a freaking week to change ! Luckily I just got a mid-rise lift. Every State offers a waiver which for me is Pa. Engine total rebuild in 2010 to cure SAI error. Also, replaced imploding pre gas tank and gas cap. 100% emission free but CEL fails the thing every time regardless. AUTEL has a $20 OBDII reader which if your SAI is clogged get to the emission station before the CEL shows. Just let AUTEL tell you when the readiness for SAI sensor hits and then gettie-up before the brain yields the CEL; used to work for me every year until the #3 piston leaked oil and thus the rebuild. Now no SAI error.

Lorenfb

The other day a '96 993 was driven (2 trips, 45 min) to set the monitors (readiness codes).
Each time the SAI test was run, one side indicated a min O2 voltage of 56 mv and the other
side indicated 14 mv. Each time the SAI test passed. So the O2 voltage, per the DME ECM,
can be as high as 56 mv and pass on a '96 993.

C4S993

I have a 1996 C4S and after multiple trips, and just about in the red on the gas left, still SAI+CAT+O2+02 heater not ready yet.

Just curious if others have noted that when the SAI at last reaches it rediness status that there is a grace period, or RS delay, until the CCU actually emits the CEL On status ? I have found that it is about 50 miles before the CEl actually is ON. Thus perhaps your example was tested during this grace period ? (eventually the SAI will reach CEL ON status). Thus, if there was a way to extend the grace period to inifinty the CEL would never reach ON.

craig001

Here is what my Durametric gave me:

Bosch Digital Motor Electronics Motronic 5.2
Module Identification


Block 0 (ECU Type) M07
Block 1 (Porsche Part Number) 99361860400
Block 2 (Vendor Part Number) 0261204008
Block 3 (Software Number) 1037355481
Block 4 36950001204


Current Fault Codes

35:
Oxygen sensing range 1||Cylinder (4-6)


27:
Oxygen sensing range 1||Cylinder (1-3)

IIRC going to the fault code section showed me low voltages. Maybe I do not need this board, but rather need to replace the O2 sensors?

C4S993

I just installed the two right side 02 sensors, easy with 22mm spanner. I have the left side two 02 sensors ($110 ea from Vertex with the correct grey+black connectors) but not installed them yet. This following several errors that failed State emissions on my 172k miles 993 C4S. Also, found broken belt in the dist and RL member sold me a rebuild dist for $500. Also, replaced all 12 plugs (used BOSCH over Berus) and now I am awaiting the readiness codes to become active. I am on my 2nd full tank trying to get the codes ready for re emission State inspection. So far no readiness on several sensors but so far no CEL either !

If I were you I would replace all 02 sensors as then you will not have issues with much older 02 sensors yielding out of spec readings. BUT FIRST, inspect the air cleaner, is it dirty ? Also, inspect the Mass Air Flow sensor.The MAF element can be cleaned. Try un plugging and re plugging in the MAF sensor connector. Also, check for an air leak from one of the many vac lines. By chance is the fuel evaporator showing signs of imploding, if so the gas cap could be bad or the fuel vapor cannister may be replacing.

BTW: I had the total $12k rebuild two years for constant SAI errors and at the moment still no SAI errors. Current problems were random misfires due to broken dist belt and now too rich on one side (which i hope the new 02 sensors fixed).

william_b_noble

as I recall, the SAI test requires that you idle after cold start for about 5 minutes twice.