Reynard38

OK first let me say please no flames from any "boy scouts" out there that feel the need to point out how evil this would be. This solution would seem to be the best one yet presented for a problem that most of us will probably face at some time (until PCNA steps up to the plate and proposes a real fix). I showed the diagram to a friend of mone this morning who is familiar with electronics (he builds speakers and studios) and he thinks the idea is sound. He also directed me to a person who may be able to build the "box".
If anyone here is interested in this PM me. By building several we may be able to save some $$ and I want to get as many heads together to determine the best way to connect it into the car.

Lagavulin

I'm in.

I've always wondered whether it could simply be turned-off in the computer's programming.

g_murray

I agree wholeheartedly.

I categorically state,, that as a LONG TERM owner, (i.e. I plan on keeping the car for a VERY long time!) that if I ever get the SAI CEL I DO plan on using the electronic fix. Why? Well for one, the "SAI system, is a BS half-a$$d attempt on improving/cleaning up emissions for 2 mins upon engine startup. It's NOT part of the 'programming' for cars, e.g. in the UK ...so what does THAT tell u, that we, Americans, are somehow 'special'. Phooey! (Let's not forget, our cars are "world cars".) And finally, the 'apathetic' approach that Porsche itself has to those unfortunate enuf to get this CEL even tho' we know (and it's been discussed here ad finitum) that it's a flawed design. And I for one am NEVER going to fork over $500 or so of my hard-earned money just so that someone can do the 'SAI-flush-fandango' just so that a bulb on the dashboard will go off.
(Have I ranted enuf?)

Now onto more serious things...

I've found (on my wild west searchings) not one but TWO electronic circuits...and would like to know WHICH one is the 'more recent/up to date one'. (they both probably work ...but hey, that's like a joke I saw recently:

A scene from the stone-age... a stone-age salesman selling 'wheels' to a prospective customer. Behind him are 'wheels' of various shapes ...most are actually squares ...but the 'modern' one he's trying to flog is shaped like a triangle.

The sales pitch is: Because it has one less bump.

:-)

(OK, I feel much better now that the voices have stopped)

Here's both circuits...

Reynard38

I'll take both diagrams to the fabricator. Does anybody here know the exact voltage the ECU wants to see from of the O2 sensors when the pump is on?

hoggel

According to the factory repair manual the measurement at pins 3 and 4 of the O2 sensor connector varies between 150mV and 900mV depending on mixture composition. The air from the auxillary air pump should make the O2 sensor detect a lean condition (<450mV).

The description of the auxillary air pump testing says that with the pump running the sensor voltage approaches 0 volts and the oxygen sensor regulation approaches 1.20 volts.

vjd3

Somebody designed and made one of these things a while back as I recall ... I have a 95, so didn't have to worry ;-) ... but you might check the archives on it.

cabrio993

I was told very unofficially by a service rep in a well known Atlanta P-car dealership that... "there is a device floating around on the internet that you can buy for $100 or so that will fool the system into believing that the SAI circuit is not clogged"...he just said to do a search and that he couldn't tell me more and that he has seen it on customer's cars....

That was about 7 months ago...I have done searches but I have come up empty. I haven't really pursued it as I don't have the CEL.

dbf73

Has anyone ever tried to inject the air into the exhaust manifold somewhere upstream of the cat to achieve the same end result without having all of those easy to clog passages?

911CabSteve

The electronic guys out there should be able to figure this one out pretty easily with the given voltages required under no CEL "normal" operating conditions. We just need to feed the right amount of current into the right places to fool the computer..

Lets find an easy electronic solution and we can all put this one to bed....Forever...

cbracerx

Sign me up!

Mike J

All you have to do is clamp the the output of the O2 sensors to ground (or close as you can get with a transistor) when the pump is running. Its a voltage thing not really dependant on the current. You also have to have zero effect on the O2 sensors when the pump is not running. This is what the transistor does in both the diagrams. The one on the right is a simplified one in that the diodes isolate each of the O2 sensors but they all can be dragged towards ground by the transistor. It looks like it should work. To test this you need a test mule that is a car that has the SAI codes repeatably on so you can be sure it works. To test variations you will need other cars to test the intermediate mock-up. The original designer of the circuit had the circuit installed on the car for several months and it seems to work great. I can't test it on my car since it does not (and will not for a while) have the SAI problem. Its pretty simple to mockup the circuit for testing ; who is going to put their cars/wiring harness/DME up for the testing?

Be wary of commercializing it though....any device pluging into an electrical sysrtem (especialy one as expensive as the 993) had better be tested and built right, and the seller had better make sure he has is butt covered by liablity insurance in case he wires or makes a mistake and poofs the DME for example, nevermind the EPA. This is why I never pursued it...but if I had the problem I will build the circuit for myself for sure though!!

Cheers,

Mike

flyenby

I am also interested,,,,,,,,,,,

kkim

For those looking to build and for those looking to buy, this is very good advice.

aaronutk

I'm an EE and up for building/testing this on my car ('97 w/SAI CEL). I thought I had read in the past that someone knew the AMP connector part number, but that it was hard to find. If someone knows it, I may be able to source it.

I'm not sure if I would be up for building or selling these things for liability reasons, but I would be willing to document everything. A bare PCB that you source parts adn build maybe acceptable.

cabrio993

I think we are on to something here. The legal experts can chime in...but maybe if it's made available in kit form, then you would be released of the liability?