View unanswered posts | View active topics It is currently Thu Dec 14, 2017 8:53 am



Reply to topic  [ 5 posts ] 
BMW E36 O2 sensor circuit, strange design 
Author Message
LQFP144 - On Top Of The Game

Joined: Sun Jul 13, 2008 2:58 pm
Posts: 331
Location: South Wales, UK
Today i went and fitted my techedge WBO2 kit to my 2.5 M50.
I wanted to keep all the wiring harness totally stock just in case i sell the car at some point and want to remove all my trimmings.
So i used the old wiring and 4 pin O2 sensor connector to access power and signal lines back to the ECU.
What i found was that the sensor does not have any power until the engine is up to operating temperature.

In this instance what I did was make a shorting link between pins 2 and 6 of the O2 relay socket.
This bypasses the relay contacts, and because the power to the O2 relay is controlled by the Main ECU relay is comes on with the ignition and goes off about 5 seconds after the engine shutoff.

I can take pix if anyone is interested and provide diagrams, it started raining today so i had to run in quickly. :cry:

_________________
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1


Sun Aug 03, 2008 10:59 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 14912
Location: Home sweet home!
I think you will find that the ECU is actually measuring the resistance of the sensor during that warm up period. I *think* innovate mentions how to fake this in their manual. It might throw a trouble code if you don't fake it. The ECU only reads the sensor after it determines that it has warmed up. It could be different on your BMTroubleYou, but have a read up on this style of operation anyway :-)

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Sun Aug 03, 2008 11:41 pm
Profile WWW
LQFP144 - On Top Of The Game

Joined: Sun Jul 13, 2008 2:58 pm
Posts: 331
Location: South Wales, UK
Fred wrote:
I think you will find that the ECU is actually measuring the resistance of the sensor during that warm up period. I *think* innovate mentions how to fake this in their manual. It might throw a trouble code if you don't fake it. The ECU only reads the sensor after it determines that it has warmed up. It could be different on your BMTroubleYou, but have a read up on this style of operation anyway :-)

Fred.


Looking at the schematic in the bentley manual the heater is fed from the relay alone there is no way for the ECU to sense the resistance across the heater pins. :?:
The output from the ECU to activate the relay only gets pulled low when the coolant is up to it normal operating temp, usually the middle of the temp gauge.
I'm just wondering if the standard ECU ignores what is present on the NBO2 line during this warmup period or if it takes it into account all the time when its in the cruise area of the map of course.
What I do know is that the original sensor probably 15 years old! was shot as it was always running slightly rich lambda of 0.96. now it idles and cruises at 14.7 or 1.00 and the exhaust smells hot and acryid with no petrol smell just as it should.
Not that i'm advocating sniffing exhaust fumes of course but its a good general indicator in the absence of a proper bonefide gas anyliser which i don't have hanging around ;)

_________________
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1


Mon Aug 04, 2008 12:31 pm
Profile
Moderator
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 14912
Location: Home sweet home!
I didn't mean sense the heater resistance, I meant sense the actual sensor element resistance/impedance. It could be that you are right and it bases it's "will I use the o2 sensor" decision on coolant temp as this is probably similar to when the o2 sensor is warm. It could also be the case that the o2 sensor gets warm at the same time as the coolant and the ECU decides to use it then. Of course the chances of that are slim considering it still works the same when all disconnected etc.

The ECU is almost certainly ignoring the sensor when not warm because they are GROSSLY inaccurate until up to temp properly.

Exhaust fume sniffing is a great indicator and the CO build up is over rated ;-)

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Mon Aug 04, 2008 1:17 pm
Profile WWW
LQFP144 - On Top Of The Game

Joined: Sun Jul 13, 2008 2:58 pm
Posts: 331
Location: South Wales, UK
Fred wrote:
Exhaust fume sniffing is a great indicator and the CO build up is over rated ;-)

Fred.


But i guess for closed loop analysis its a little inadvisable to route a hosepipe into the cabin???? :lol:

_________________
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1


Mon Aug 04, 2008 6:54 pm
Profile
Display posts from previous:  Sort by  
Reply to topic   [ 5 posts ] 

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF. ColorizeIt.