rpaitich

re: SAI error on OBD2 993
I'd appreciate it if someone with intimate knowledge of how the SAI error is detected would tell me exactly what is detected. Is it back pressure? O2 sensor activity? I'm technically competent, so give it to me in any terms you like.

I'm looking for a way to trick the computer so that it does not recognize the SAI error. As I understand, upon starting, the air pump comes on for one minute (for a cold engine). If it finds the secondary air jets are clogged you get a P0410 error (maybe others too?). I speculate that if I allow the outlet of the air pump to simply leak into the air, it will not detect the clogged jets. If so, i could just put a hole in the hose and allow it to exhaust into the air. If i need to seal it off after it has run, I could add an electrically operated air valve.

goofballdeluxe

If it were only that easy <sigh>.

There is no easy answer, other than clearing out the clogged SAI ports. Some have had success using solvents and a bass guitar string, but I'm sure others will chime in.

Suffice to say, you're not the first to be plagued by SAI codes. Many, many greater minds than I have failed to find a quick and easy shortcut fix.

Good luck.

rpaitich

goofball:
Thanks. But can you tell me what is being sensed, that knows the SAI ports are clogged? (Or is that part of "There is no easy answer"?)

Cincy_Ron

My understanding is that it's getting data from the O2 sensors. Luckily I haven't had to deal with this yet (knock on wood). There have been a bunch of threads discussing how the system works, bypass fixes, SAI signal simulators, etc. Click on "Search this thread" while you're in the 993 forum, then click on "advanced search", type "SAI" in the keyword search box and from the dropdown menu below it change from "search entire post" to "search titles only". Lots of good threads. I thought the SAI Signal Simulator thread was interesting.

Ed Hughes

This is why a '95 is worth $1,000,000 in Calif.

FisterD

There is a black box fix out there. It does simulate 2 of the o2 sensors to trick the system. Do some searching and you may find more info.
Also the SAI flush is no big deal. I did it over 20k miles ago and still going strong.

2Many Cars

It's the O2 sensors. The sensor upstream of the cat needs to read a rich O2 mixture at startup or it will trip a code. The SAI runs a few minutes after startup to feed extra O2 to the cats to help them fire up. Various work arounds have involved either adding bungs to the exhaust to inject air just up from from the upstream sensor or electronics to fool the sensors into seeing more air at startup. It gets complicated because the system has to kick off after a few minutes otherwise the injection system will get bad readings and create a host of problems.

axl911

It will be hard to trick it. At a certain time after the engine starts up, the car will compare O2 readings (not sure if just post-cat, or both pre and post) based on the amount of air injected by the SAI. The OBD2 manual showed a step function but no idea on time and voltage in the graph.

User 122821

On cold engine conditions, the ECU starts the air pump via a relay. With the ECU running the air pump, it expects the O2 sensors to report a lean mixture (more 02 injected at the exhaust port, thus lean reading). If the ECU does not get a lean mixture reading from the O2 sensors (like when the air ports are blocked), it throws the P0410 error. The P0410 is for just one side on the engine. I forget the other side error.

To trick the ECU, the O2 sensors must be lean only when the ECU signals the air pump. So O2 bungs, resistors, etc will not work since they are not depend on whether the pump signal is on. What is needed is a circuit to ground the O2 sensors (lean reading) when the air pump voltage is on. This can be done with mechanical relay or a transistor relay.

User 122821

I used the circuit from this post

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

CalvinC4S

Flying low is 100% correct on the function.


Plug the SAI ports in the head with the blanks from Patrick Motorsports.
Add a 1/4" ID hose from the SAI Pump to a welded in bung just after the input flange
of the Cat.

I have seen this system work for 7 years now with no issues. (not my work or car, but it works)

The fault is from the second set of O2 sensors.

It took a few attempts finding the right location and hose ID, then it just works.

2Many Cars

As Calvin observes this will work if you use air input from the existing air pump as it shuts down when it should. All you're really doing is rerouting the flow around the clogged ports.

fullbooker

Ron,
I can help you "trick" the system enough to pass smog. Let me know next time you need to get car smogged.
Phil

rpaitich

Phil, Thanks. I think i know how to contact you.
Ron

rpaitich

Calvin,
The two O2 sensors you refer to, are they the ones before the CAT?
The electronic method that flying_low mentions above is appealing, and could be applied to these two sensors. I'm a EE, so this is in line with my skills. A friend teases me, "When electronics is your hammer, many issues in control systems become your nails." ...or something like that.