The banner above is an advertisment - if it asks you to download software, please ignore.
Site News - 7/1: Members: Log In to See Fewer Ads! | 5/28: SAAB Evolutions/TSN T-Shirts $14
[General | Members | C900 | 9000 | NG900 & OG93 | 93 | 95 | NG95 | 99 | Sonett | Vintage Models | Clubs | Other Cars | FAQs | Gifts | Member Photo Galleries | Member Directory | Classifieds | Manuals | *Buddy Registry | *Mileage Registry | Polls | What's New | Raffle | Photo of the Month | Sponsors]

C900 Bulletin Board
1979-1993 & 94 Conv [Subscribe to Daily Digest]
(Search Author's Posts: e.g. Keyword:username)*Members Only

[Main C900 Bulletin Board | BBFAQ | Prev by Date | Next by Date | Post Followup ] Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Re: O2 sensor...what the devil?
Like This Post: - Subscribe to Daily Digest for this Bulletin Board
Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Thu, 8 Mar 2007 08:37:12 Share Post by Email
In Reply to: O2 sensor...what the devil?, Max84T, Wed, 7 Mar 2007 14:14:41
Alert me when someone posts in this thread:
Members do not see ads below this line. - Help Keep This Site Online - Signup

I'm not sure what the Bentley reading is, but once you've disconnected the O2 sensor from the ECU, the control loop is broken. The ECU is trying to schedule fuel based on the O2 reading.

With the sensor disconnected, a reading of 0.08 indicates lean running. That value doesn't mean the sensor is necessarily bad - if the engine is running even slightly lean, the sensor could be telling the truth. Typically the ECU defaults to a richer mixture with a bad O2 sensor signal (and a disconnected sensor would do that).

What would be more interesting is what the sensor reads when it IS connected to the ECU. Ideally, it should be cycling between about 0.2 and 0.8 volts at about once per second. I'll bet that you will see the sensor stuck to one side or the other.

How do the plugs look? Do they look the nice light grey of a good mixture, or are they the stark white of lean running, or the fluffy black or rich?

Let's just assume that something is causing the engine to run lean. Maybe a vacuum leak, maybe low fuel pressure. With the O2 sensor disconnected, the ECU simply schedules a richer mixture and leaves it there, but even that isn't rich enough to be stochiometric, so the sensor reads near zero. Remember, the sensor only operates in a VERY narrow band of rich to lean. Lean is 0 volts or so. Only a little lean is also 0 volts or so. A little rich and rich are both 0.8 volts or thereabouts.

Now, when the sensor is connected, the ECU sees that the sensor is connected, but is seeing a lean reading. So it tries to richen up the mixture. It'll mess around with the fuel ratio to try and get there. It may even be trying to run rich. The thing about running rich is that it can cause cough and sputter just like running lean.

So - what do the plugs look like? And what is the reading (at idle) from the O2 sensor when it is connected?

posted by 192.249....
Posts in this Thread:
Alert me when someone posts in this thread:
Members do not see ads below this line. - Help Keep This Site Online - Signup
Post a Followup

No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.

Name: Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
E-Mail: (Optional)
Re-Enter E-Mail: (Confidential & Secure - Not revealed to other users!)
Note: Please check your spam folder for BB responses.

Subject:

Posting rules are simple - No for sale/wanted ads may be posted here - use the site classifieds.
You may not cross-post your message to multiple BBs.
Not permitted: political/religious topics and being disrespectful (personal attacks, insults, etc...).
 Site Members do not see any red text, inline ad links, bottom of page anchor ads, box ads, or anti-spam check.

Message: (please no for sale/wanted classifieds - post those in the Saabnet.com Classifieds)
Links are now automatically made active, no need for any special code (or use the Option Link field below) - don't put links in () or end with a '.'
To add inline images to your post, use [img]http://www.domain.com/img.jpg[endimg] (or use the Optional Image Link field below).

Links are now automatically made active, no need for any special code (or use the Option Link field below) - don't put links in () or end with a '.'
To add inline images to your post above, use [img]http://www.domain.com/img.jpg[endimg] (or use the Optional Image Link field below).
Optional Link: (e.g. http://www.saabnet.com/)
Link Title: (Optional)
Optional Photo/Image Link: (e.g. http://www.saabnet.com/img.jpg)
Photo/Image to Upload: (Please be patient while file uploads)



StateOfNine.com
SaabClub.com
Jak Stoll Performance
M Car Covers
Ad Available

The content on this site may not be republished without permission. Copyright © 1988-2024 - The Saab Network - saabnet.com.
For usage guidelines, see the Mission & Privacy Notice.
[Contact | Site Map | Saabnet.com on Facebook | Saabnet.com on Twitter | Shop Amazon via TSN | Site Donations]

Random Saabnet.com Member Gallery Photos (Click Image)
This is a moderated bulletin board - Posting is a privilege, not a right. Unsolicited commercial postings are not allowed (no spam). Please, no For Sale or Wanted postings, SERIOUSLY. Classifieds are to be listed in The Saab Network Classifieds pages. This is a problem solving forum for over 250,000 Saab owners, so expect to see problems discussed here even though our cars are generally very reliable. This is not an anything goes type of forum. Saabnet.com has been a moderated forum since 1988. For usage guidelines, see the Saabnet.com Mission and Purpose Page. Please remember that you are not anonymous. Site Contact | Site Donations | Other Sites by SP - Poverty2Prosperity.org | Run Club Menlo Park | ScreenBot


Site Members do not see red text instructions, bottom of the page anchor ads, or box ads.
Click here to see all the Site Membership Benefits!