O2 Sensor - BMW Forum

M3wannabe2004 · 08-28-2005, 03:22 PM

Right, on my list of things to-do on my 1991 325i is to change the O2 sensor, so, today I drive the car up onto ramps, prepare myself for the mission and decided that before i would change the sensor I would see how the car ran without it!. I disconnected it from the loom and started the engine..... waiting for the engine to run like a hound... it never did! it was exactly the same as before!! does this mean that my O2 sensor has always been broken?? and I have never experienced the car with a working O2 sensor BTW there was no check engine light on the dash, although the Sensor had been totally disconnected... Any views much appreciated.

Delmarco · 08-28-2005, 04:29 PM

Quote:

Originally posted by M3wannabe2004@Aug 28 2005, 02:22 PM
Right, on my list of things to-do on my 1991 325i is to change the O2 sensor, so, today I drive the car up onto ramps, prepare myself for the mission and decided that before i would change the sensor I would see how the car ran without it!. I disconnected it from the loom and started the engine..... waiting for the engine to run like a hound... it never did! it was exactly the same as before!! does this mean that my O2 sensor has always been broken?? and I have never experienced the car with a working O2 sensor BTW there was no check engine light on the dash, although the Sensor had been totally disconnected... Any views much appreciated.

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holy shit!
That is they most important thing to have connected to your car...Dude It's the lungs of your engine!

Your car is like a human...no O2 sensor means no oxygen means no fuel combustion means car sitting dead on lot!!!!

Plug that shit back in ASAP!!!

It costed me $480 at the dealership to replace that alone.

BTW is your car an E30 or an E36(like in my sig)...
I laways thought 1991 3 series were E30s...
which might be good for you because the O2 sensors on the E30 are cheaper to replace than E36 cars...

(i think)

rwall23 · 08-28-2005, 07:15 PM

Correct me if I'm wrong, but I'm fairly certain that all the O2 sensor does is checks your exhaust to see how much oxygen is in it, so that way it can tell the computer whether to richen or lean out the fuel/air mixture, I think your car would run without one, you would just get poor gas mileage...

Hamfisted · 08-28-2005, 07:53 PM

Quote:

Originally posted by M3wannabe2004@Aug 28 2005, 04:22 PM
Right, on my list of things to-do on my 1991 325i is to change the O2 sensor, so, today I drive the car up onto ramps, prepare myself for the mission and decided that before i would change the sensor I would see how the car ran without it!. I disconnected it from the loom and started the engine..... waiting for the engine to run like a hound... it never did! it was exactly the same as before!! does this mean that my O2 sensor has always been broken?? and I have never experienced the car with a working O2 sensor BTW there was no check engine light on the dash, although the Sensor had been totally disconnected... Any views much appreciated.

[snapback]373008[/snapback]

Yeah '91s are E30's so there's only one O2 sensor. It will run without it but it defaults to the full rich mode and your gas mileage will suffer. You should eventually get a Check Engine light, it may take a few miles. Yes the O2 sensor tells the ECU whether to richen or lean out the fuel mixture via the fuel injectors. It's about $50 to replace it so I would just install a new one if it's got 75k miles on the old one or so.

E30 O2 Sensor Replacement Article

Mike

zeidakiss · 08-28-2005, 09:34 PM

he has a 92 that was prob just a typo

it says in his info thingy on the left.

Dudesky_E36 · 08-28-2005, 11:10 PM

'91 & 92 use the same single sensor.

drz · 08-28-2005, 11:23 PM

Quote:

Originally posted by rwall23@Aug 28 2005, 07:15 PM
Correct me if I'm wrong, but I'm fairly certain that all the O2 sensor does is checks your exhaust to see how much oxygen is in it, so that way it can tell the computer whether to richen or lean out the fuel/air mixture, I think your car would run without one, you would just get poor gas mileage...

[snapback]373026[/snapback]

You are correct. That is what the oxygen sensors do. They are not the lungs of your car. It is not recommended to run with a faulty one or without one, however. Also, you will get the CEL to light pretty soon if you run without one, which could disguise more serious problems. Most certainly you would get very poor gas mileage and or accelereation/throttle response, because the engine management system would be getting faulty information. OBDI is more forgiving than is OBDII, but I assure you that the $120 and short time it will take you to replace it is worth the trouble.

drz · 08-28-2005, 11:23 PM

Oh -- also, I seriously doubt you will pass emissions testing missing an o2 sensor.

Delmarco · 08-29-2005, 12:17 AM

S how come when my O2 sensor failed, my E36 1995 M42 would not even start...?

The dealership explained to me what te O2 sensor does and that "lungs" scenario is what I was told....before coughing up $480 to replace it..

What's goings on?

catalyst. · 08-29-2005, 12:53 AM

Your car wouldnt even start?

Ussually (on e36's at least) the ecu will put the engine in limp mode, and it will run extra rich, and generally like shit.

Delmarco.. $480 for ONE 02 sensor ..what a goddamn rip off.. i wonder what they charge for OBDII.. $1000?

brand new the sensor is what 120? I cant imagine its to tough to replace..

obd2guru · 08-29-2005, 03:44 AM

omf"g" you got nailed delmarco , damn ,ohh well looks like ur happy ,i wish i can have customers like u

. anyway o2 sensor health is very important ,if you dont have one your car will never go to closed loop that means it will run on default values and not rely on any sensor input.

vwk · 08-29-2005, 06:40 AM

I have an '91-er E36.. only condition is that you have to live in europe, there they're delivered from oktober '90.... So it could be possible, yes

Gkamysz · 08-29-2005, 10:37 AM

O2 sensor does nothing until the exhaust has heated up substantially, read operating temp. The ECU runs the engine open loop until it gets a valid reading form the O2 sensor. This is usually about the white tick mark to the left of center on the temp guage in mine. I can actually tell when it has switched to closed loop by watching the mileage guage. When it goes closed loop it burns significantly less fuel.

The ECU does not use the O2 readings to start the engine.

Dudesky_E36 · 08-29-2005, 11:42 AM

^^^Correct.

NESS · 08-29-2005, 01:36 PM

I replaced my 02 sensor and Im still getting 16.6mpg. I was getting 16.8mpg before I replaced it. How long does it take for the OBC to update the mpg? And could my OBC be wrong? Cause the car feels like its not burning as much gas anymore a quarter tank lasted alot longer than it did before I replaced it.