993_Targa

Crazy idea:
It appears there may be 3 Bosch ECUs for the 993:
0 261 204 008 '96
0 261 204 376 '97
0 261 204 649 '98

Would it be correct to assume the "circuit" only works on the '96 008 ECU? (The one that requires a memory adapter for performance upgrades)

Assuming ECUs are swappable across model years and the plugs are the same, would it be feasible to swap out with a '96 ECU and install the "circuit" for a week or two to get my car back on the road?

Just trying to get a bit creative here

Jim
PS William sorry to hear your 993 was stolen... that always sux unless it was massively over-insured! I may try the flush soon if I can't get a circuit solution figured out.

993_Targa

Important questions:

1. Could someone please confirm which O2 sensors are involved in the SAI test?
2. If for some strange reason the rear O2 sensors (behind the cats) always reported they were "in an acceptable range" would this pass the test?

Thanks in advance for clarifying this!
Jim

Lorenfb

"1. Could someone please confirm which O2 sensors are involved in the SAI test?"

the front ones

"2. If for some strange reason the rear O2 sensors (behind the cats) always reported they were "in an acceptable range" would this pass the test?"

No!

Find someone (shop or 993 owner) with access to a Porsche tester (PST2
or PIWIS) and you can 'force' the SAI test and watch as the test runs
viewing the actual O2 sensor values. A must test when doing a PPI.

william_b_noble

I think you are giving short shrift to the scanners - the above may be true for some really cheap scanners - the unit I have will read dynamic data and will show the individual readiness flags as they are set, but it will not tell you if you have passed one of two required trips. The hard flag to set requires driving at a particular speed at a very low (but not zero) throttle setting for something like 45 seconds - I could only set that flag on a particular set of rather level road where at 30 mph in third gear I would get into the right power range, RPM range, etc. The manual tells you how to set the flags if you have a Bosch Hammer.

Lorenfb

"I think you are giving short shrift to the scanners - the above may be true for some"

No, don't think so! Worked on too many 993 setting the monitors. None appear
before all are complete. Used many scanners including both the PST2 and the
PIWIS and NONE show any completions until ALL are complete.THAT"S THE
PROBLEM! Many look at the basic simple tests and assume that's the monitors.
No wonder so many have problems and don't know the basics of setting the
OBDII monitors. Read here for more info under 'Porsche 993 Cycle Flag Basics';
http://www.systemsc.com/codes.htm

Bottom line: A minimum of two trips, in some cases ('96 993) three, are required
before any monitors appear. You'd think by now with all the posts, most would
understand!

william_b_noble

ok, I will believe you that "none show any completions until...", but then could you help me understand what my reader is telling me when it shows the half dozen or so "readiness tests" and which ones have completed and which ones are not - it must be something other than readiness tests completions if I understand you correctly. The reader I'm using is the AutoX-ray EZ-Scan 6000.

Lorenfb

"but then could you help me understand what my reader is telling me when it shows the half dozen"

It indicates that those key system elements are operating but not have completed
the required OBDII testing requirements, e.g. the SAI system element does operate
but no evaluation of its effectiveness has been performed per the ODBII specification.

acrabtree0536

I'm mostly a lurker, but have been moved to email and get on this list if it isn't too late. See some of you on the 993Fest i hope.

Adam
www.sportscarguyspeaks.com

rpaitich

I made a minor contribution to the circuit shown in flying_low's posts to "Recap of the SAI circuit" (FETs instead of bipolar transistors).

This circuit has worked for several Forum members. It bypasses the O2 sensors while the SAI pump is running.

I may have a simpler solution and would appreciate some info so that I can refine my idea.

As I understand, the SAI pump runs for a specific time (two mins?) and runs ONLY when the engine is below a certain temperature, like cold morning starts. The fuel mix is enriched to heat the CAT more quickly, thereby reducing emissions. After the specific run time, the SAI pump shuts off. If the SAI ports are clogged, the pump sees back pressure (or the O2 sensors show excessively rich) and you get the dreaded CEL P0410.

My idea is to trick the temp sensor, so that the SAI pump never comes on, and the SAI test is ignored by the computer. The minor downside is that the CAT won't heat up as fast. I'd do this every time the ignition is turned on, and trick the temp sensor to think the engine is at a temp above the temp that would turn the SAI on.

If you see a flaw in this thinking, let me know some details.

If this may work, someone please tell me where to find the temp sensor, and if you have the resistance values for cold and hot, let me know.

I'll be happy to post results of this when/if I get it working.

Ron

C4S993

That may explain why my '96 had a sweet spot whereupon after all the required Pa State sensors had reached readiness than it would pass emission tests. However the sweet spot only last for maybe 30miles and then the CEL appears. So maybe the ECU is not so quick to reply CEL when it sees it's sensors ready.

PS: just'sayin, my engine was rebuilt 40k miles ago. But of late the CEL reappeared! ! Looked at SAI ports and all were open and carb cleaner raced throughout SAI rails with no obstructions. So replaced plugs and now no more CEL!

mgianzero

I'm up for trying one of these circuits on my '96 as another test as I understand you've had the most success with the earlier year types.

If it does appear to work, then would I be able to remove my SAI pump and hoses or do they need to stay?

Where can I order one of these boards?

Marc

User 122821

I've had low success results with the circuit. In looking at the SAI system there is another variable not accounted for in the circuit. There is a vacuum control valve on the back of the engine which controls the flow of air into the SAI passages. I imagine there is times when the pump is on but the valve blocks the flow which the ECU is aware.

While the current circuit is a good start, it will need more research to be effective 100% of the time. I've taken the path of removing the circuit from my car and clearing the SAI passages with the brake cable method.

rpaitich

One of our Rennlisters made a circuit to bypass the O2 sensors when the SAI pump is running. This was to deceive the ECM into thinking there was no SAI error. I've heard mixed reports on success or lack thereof. I'd appreciate anyone letting me know whether this worked for them

Ron
'96 993; no SAI errors (yet)

william_b_noble

I built that circuit on some perf board, installed it and verified that it worked as designed but it did not eliminate the SAI error on my 97 and it caused the detection of some other fault (dont' remember what) - the car was stolen in 2012, so that's one way to be rid of the pesky SAI problem. I'd say that the solution may work for 96, but most assuredly does not work for 97.

Mr.Woolery

I have a '96 and am interested in installing this on my car as a "preventative" measure (I'm not having any SAI issues). If anyone is willing to sell theirs, please let me know.