Author Topic: Adding o2 sensor on m42 (Read 5154 times)

Bracky · « **on:** March 08, 2010, 08:34:08 PM »

Hi all first post so go easy on me if I make any mistakes.
I have a 1991 318is which did not have an o2 sensor from factory and would like to add 1. Ive fitted the bung and sensor to the correct position in the exhaust but need help with the wiring side??
Any help would be appreciated

Bracky · « **Reply #1 on:** March 14, 2010, 09:40:08 AM »

Just found that the connector (C140) and that its located on the bulkhead under the battery tray. Will have to wait to get to a scrap yard to get the cable from C140 to the o2 sensor but couls till do with someone to confirm if the ecu will just recognise and adapt to use the sensor appropriately or if theres more involved with this??
It would be greatly appreciated if anyone could help me with this.
B Paice

BlueBMW · « **Reply #2 on:** March 14, 2010, 10:26:06 AM »

My understanding was there is a catalytic converter plug that is connected when there is no cat and is disconnected when there is. Do a search around these forums and you'll find it. Some call it the evil cat plug. I'd think you'd disconnect that so the DME knows to use the O2 sensor for mixture purposes.

Bracky · « **Reply #3 on:** March 14, 2010, 02:29:38 PM »

Cheers thats soundsabout right for BMW but ive googled it all day and still not fand any relivent info and a search of the forums just ends up with every thread with the words cat or plug in them but have trallled though and still cant find anything. Can anyone tell me where this plug is situated on the car or any links with relivent info on this plug??? like I said previously I've found the sensor connector under the battery tray (C140) but this never had any blanking cap/plug and was open to the eliments so I'm guessing there this plug must be elsewhere.

BlueBMW · « **Reply #4 on:** March 14, 2010, 04:57:13 PM »

http://www.m42club.com/forums/showpost.php?p=65413&postcount=6

Bracky · « **Reply #5 on:** March 16, 2010, 03:39:14 PM »

cheers that was perfect, thanks for your help.

SonomaGTLN2 · « **Reply #6 on:** March 20, 2010, 10:51:03 AM »

Not to thread jack, but how does the car run without the O2 sensor in the european cars? I assume it relies mostly on the AFM for managing A/F ratio?...In that case, I have been getting an O2 sensor CEL so I plugged in the one-terminal connector (which is unplugged on cars with cats) and unplugged the O2 sensor thinking it would be configured like a euro-spec model...As soon as it was under load or above 50 mph or so the engine would lose power and essentially stall...strange because even with the CEL the car appears to run fine with the O2 installed and the one-terminal plug either plugged in or not.

SonomaGTLN2 · « **Reply #7 on:** March 20, 2010, 01:37:23 PM »

Follow-up...I attached a probe wire to the voltage feedback portion of the O2 sensor and revved it at 2000 rpm to heat up the sensor. First I did this with the one-terminal no-cat wire plugged in. Strangely, the sensor output never reached 0.45V (that I expected if the A/F ratio is correct)...it was between 0.6 and 0.9 V (showing it's running rich?). Next step I unplugged the one-terminal no-cat wire on the harness and revved to 2000 rpm. While holding it there, it was right between 0.44V and 0.46V (good news). When I let it return to idle, the voltage started climbing back up to greater than 1V (actually up to 6 or so volts, until I revved it again for a few minutes). This leads me to another question, at idle should my O2 remain at 0.45V, or does it cool down too much because less heat is traveling out the tailpipe? Is the O2 sensor heating coil only on when in closed loop, or is it on all the time?