Unpluged o2 but no check engine light

[Dodobrown]

Just recently i though i had fixed all my issues but no... on my way to AC the other night while on the highway my check engine light went off(usually on for o2) and i lost all power. it felt very similar to a bad tps sensor, although i had just recently replaced it so i would have to assume its still ok.

Now the car will run ok with the check light on and run like trash with the light off and it will switch between on and off consistently the whole time the car is on.

Any ideas gurus?

[Dodobrown]

any one? bueller, bueller, bueller

[Sagaris]

Are you getting code 1221 or 1222? http://e30world.com/fuel/BMW-E30-DME...ic-fault-codes

I am not sure if the car defaults to open loop when the check engine light is on but if you are getting 1221 or 1222 then it sounds to me like the oxygen sensor is bad or has a wiring issue which is causing it to give bad feedback to the ECU. How new is the oxygen sensor?

[Dodobrown]

maybe about 3 months its a generic bosh 4 wire.

i find it very odd tho that the car dosnt have a check engine light with the sensor unpuged.

[ForcedFirebird]

Since I did the Motronic 1.3 swap, I have never had the o2 plugged in and it always ran fine - no check engine light in my dash since it's an early model, but the absence of o2 shouldn't make the car run bad, but a bad sensor that is connected can cause issues.

[Sagaris]

I am thinking that the car could run decently enough with the O2 and bad with it disconnected if there are vacuum leaks which the O2 sensor can compensate for when plugged in.

[ForcedFirebird]

O2 won't compensate for vacuum leaks since un-metered air is still that, not metered. Rolling idle is usually the symptom of vacuum leaks.

[Sagaris]

I am positive that you know much more than I do about Motronic and EFI in general, I am still learning and want to learn as much as I can, but wouldn't unmetered air cause the engine to run lean for that cycle then the oxygen sensor would give the ECU feedback and increase the injector pulse width for the next cycle? (sorry to be mildly off topic)

[ForcedFirebird]

Well, you can experiment. Take the regulator vacuum line off your car while it's running, then unplug the o2, next plug the vac line back in, then the o2 back in and note changes.

[Sagaris]

I will be running a wideband + logger this weekend, I will definitely play around with it.

[Dodobrown]

any one have any idea why i wouldnt be running a check enging light with the o2 unplugged? also why would i have sporadic throttle response loss? it makes me think the dem has gone bad.

[Sagaris]

According to the definition of the 1222 fault code in the link above, one reason for the oxygen sensor to trigger the check engine light is when the oxygen sensor gives the ECU voltages too high (ex. over 0.8V) or too low (ex. under 0.2V) for longer than 10 seconds. According to the list of fault codes you should be getting a 1221 code for having the oxygen sensor unplugged. Perhaps your particular ECU doesn't actually support all of the fault codes listed on that site, or maybe the ECU is buggered up like you are saying.

[Dodobrown]

hey guys though i had sloved this problem about a year ago and now my gremlin is back. i had the o2 senser replace this time last year along with my tps and its doing the exact same thing now. is there any chance that running my car with out a cat it is messing up the 02 reading perhapse fouling the sensor?

[jlevie]

The lack of a catalytic converter will have no affect of the sensor.

What fault codes are in the DME?