Notices

Recap of the SAI circuit

 
Old 09-16-2011, 02:22 PM
  #76  
Lorenfb
Super User
 
Lorenfb's Avatar
 
Join Date: May 2003
Location: SoCal
Posts: 3,513
Default

"It would be a simple circuit to design for this (voltage change), assuming the voltage levels were provided."

Probably not that simple, i.e. One would have to characterize the
actual voltage change that was required. For example, the OBDII system
may what 'see' the O2 voltage start at .45 volts and have a time constant
range of 2-3 seconds and have a minimum voltage of 20-30 millivolts.
If the desired change is not 'seen', then SAI monitor is not set and
a fault code (CEL) results.
Lorenfb is offline  
Old 09-16-2011, 02:55 PM
  #77  
ltc
Super Moderator
Needs More Cowbell

Lifetime Rennlist
Member
 
Join Date: Mar 2002
Posts: 29,318
Default

Originally Posted by Lorenfb View Post
"It would be a simple circuit to design for this (voltage change), assuming the voltage levels were provided."

Probably not that simple, i.e. One would have to characterize the
actual voltage change that was required. For example, the OBDII system
may what 'see' the O2 voltage start at .45 volts and have a time constant
range of 2-3 seconds and have a minimum voltage of 20-30 millivolts.
If the desired change is not 'seen', then SAI monitor is not set and
a fault code (CEL) results.
I thought about it for 30 seconds ... I'm pretty sure it's not rocket science.
ltc is offline  
Old 09-16-2011, 03:19 PM
  #78  
cdmdriver
User
 
cdmdriver's Avatar
 
Join Date: Jun 2008
Location: The land of Governor Moonbeam
Posts: 581
Default

I don't need it right now, but good to have just in case. Please add me to the list!
cdmdriver is offline  
Old 09-16-2011, 03:42 PM
  #79  
flying_low
User
Thread Starter
 
flying_low's Avatar
 
Join Date: Oct 2004
Location: East Bay, CA
Posts: 588
Default

Originally Posted by Lorenfb View Post
"No! All it does is fool/mis-represent what the O2 sensors 'see' when the
SAI air pump turns 'on', i.e. It basically indicates that an adequate amount
of air is reaching the O2 sensors during a cold start-up. "

The SAI system includes the not only the air pump but:
1. the O2 sensors
2. the SAI monitor diagnostics within the ODBII system
3. the relay which turns the pump 'on' and the by-pass circuit
4. air valves

So one can't really remove the SAI system!!!!!!!!

Potential Problem with the proposed by-pass circuit:

On the '97/'98 DME ECM the SAI monitor may look for a voltage
change on the O2 sensors and NOT an immediate zero volts
from the O2 sensors with the by-pass circuit. So a SAI fault
still may occur.

Bottom line: Before asssuming that the by-pass circuit is the
end-all fix for ALL 993s, thorough testing needs to be done on
all 993s, i.e. Since later/early 993 DME ECMs had different OBDII
firmwares and thus the by-pass circuit may have different effects.
Furthermore, if the by-pass circuit is not grounded in the ideal location
or the circuit is not shielded from 'noise', the circuit may not function
properly and additionally cause the O2 sensors to provide erroneous
voltages, thereby causing additional fault codes.
Thanks for the technical explanation. I do agree this is not a fix all for all cars in this situation but it is working on two 993s as data points. I will be interested in getting feedback from '97 and '98 993s.
flying_low is offline  
Old 09-16-2011, 04:37 PM
  #80  
Jeff96-993
Addict
Rennlist Member

 
Jeff96-993's Avatar
 
Join Date: Aug 2001
Location: Cincinnati
Posts: 1,807
Default

Add me to the list for an assembled board please!

Last edited by Jeff96-993; 09-17-2011 at 05:53 PM.
Jeff96-993 is offline  
Old 09-16-2011, 05:00 PM
  #81  
Kaefer
Addict
Rennlist Member
 
Join Date: Nov 2004
Location: Central VA
Posts: 89
Default

Please add me to the list. I'd like (2) of the assembled boards.

Thanks for doing this!
Kaefer is offline  
Old 09-16-2011, 05:58 PM
  #82  
SimonM_98
User
 
SimonM_98's Avatar
 
Join Date: Mar 2011
Posts: 38
Default

Please put me down for 1 of the assembled boards also.

Great work!
SimonM_98 is offline  
Old 09-17-2011, 09:18 AM
  #83  
CarreraX
Addict
Lifetime Rennlist
Member
 
CarreraX's Avatar
 
Join Date: May 2005
Location: Dayton Ohio.....Americas Playground!!!
Posts: 2,822
Default

Lewis, Please also put me down for two assembled kits! Thanks for the contribution to Rennlist! We all appreciate it!
CarreraX is offline  
Old 09-17-2011, 01:14 PM
  #84  
skypig
User
 
Join Date: Feb 2007
Posts: 13
Default

PLZ put me down for one assembled kits.......we can't thank you enough!!!!!!!
skypig is offline  
Old 09-17-2011, 04:53 PM
  #85  
Don't lift
Addict
Rennlist Member
 
Don't lift's Avatar
 
Join Date: Feb 2002
Posts: 186
Default

Sign me up for one assembled board. Thx Lewis.
_____________
'97 Blk/Blk C2S
Don't lift is offline  
Old 09-18-2011, 01:18 AM
  #86  
2ndof2
User
 
2ndof2's Avatar
 
Join Date: Sep 2003
Location: Westlake Village, CA
Posts: 1,851
Default

Please count me in for one. Thx
2ndof2 is offline  
Old 09-18-2011, 02:44 AM
  #87  
Richard W
New User
 
Join Date: Oct 2009
Location: Alberta, Canada
Posts: 4
Default

Great idea!!! Please add me to the list for one assembled and on un-assembled unit.

Thanks
Richard W is offline  
Old 09-20-2011, 01:23 AM
  #88  
MDamen
User
 
MDamen's Avatar
 
Join Date: Jun 2007
Location: Redmond, WA
Posts: 628
Default

Is there a way to check the function of the circuit before it is installed? If I apply 12 volts to the + and - is there a specific voltage or range I should see at each O2 sensor? Do they go to ground or do they show a small voltage?
MDamen is offline  
Old 09-20-2011, 02:35 AM
  #89  
Amfab
Addict
Rennlist Member
 
Amfab's Avatar
 
Join Date: Apr 2007
Location: Los Angeles
Posts: 1,201
Default

I would definitely like to be able to test my system. Put me down for one assembled.

Thanks!

-Andrew
Amfab is offline  
Old 09-20-2011, 12:47 PM
  #90  
flying_low
User
Thread Starter
 
flying_low's Avatar
 
Join Date: Oct 2004
Location: East Bay, CA
Posts: 588
Default

Originally Posted by MDamen View Post
Is there a way to check the function of the circuit before it is installed? If I apply 12 volts to the + and - is there a specific voltage or range I should see at each O2 sensor? Do they go to ground or do they show a small voltage?
The O2 voltage is grounded when 12 volts is applied to the circuit. You could setup a test O2 sensor to the circuit on a testbed with a volt meter across the O2 sensor. I used a previous old O2 sensor to testing.
flying_low is offline  

Thread Tools
Search this Thread
Quick Reply: Recap of the SAI circuit


Contact Us - About Us - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: