Oxygen Sensor 325is - e30

I have not driven the bmw much lately so I decided that tonight would be a good time to take it out with no real destination in mind. It needed gas and with the grocery store $0.20 per gallon savings I decided to fill it with 93 octane for the hell of it. I drove it about 3 miles of spirited driving after fill up and the check engine light came on. I circled back home and consulted the wisdom of Bentley which tells me it is an Oxygen Sensor.

I followed the book and reset the light by turning the ignition 5 times. After that I got about 2 miles before it came on again. On the reset after that I got only about a mile.

So, another thing to tend to but before I do I have to wonder:
Could the higher than normal octane gas have anything to do with triggering the oxygen sensor?
Is it possible that after this tank of gas and back to lower octane that it may not trip the oxygen sensor?

I wanted to be sure that the having the sensor tripped was not hurting performance so I ventured off to some country roads to verify that yes, redline in third gear is still in the 80 mph range. For conclusive results I tested that numerous times also assuring that 2nd gear redlines at 55 mph. Additionally, happy to report that the lsd is working from launch.

I run 93 all the time in mine, the car is rated for at least 91, anyway. Are you running any kind of chip?

I was under the impression US market cars had low enough compression you could run about any octane. At least on the stock ecu.

the higher the octane, the more difficult it is to burn. obvious, but it leads into other stuff i have to say. it could be that your e30 does not make high enough effective compression (go wiki the difference between effective and static compression) to burn aforementioned 93 octane. since it is not burning completely, all of that unburned fuel is going out the exhaust pipe, over the o2 sensor and it is seeing a rich condition. i dont know if your car has a modified head/deck height/piston domeage (lol i just made up a word) so i dont know what compression your car should be making, but if the cel is coming on, go back to lower octane. if that doesnt keep the light off, youre in a pickle

According to my 1991 manual, the 325i's were supposed to run 87, and the 318's 93.

Yup, my old 88 325is specified regular gas in the manual, it is only 8.8:1 compression. When I had a Turner Motorsports chip in it, I ran premium, but when I switched back to the stock tune, I went back to 87 for 40k miles, no issues.

I run 87 octane in my race car, so no, you don't need to run higher octane in the M20. We aren't allowed chips so it's all stock. My O2 sensor has apparently failed in some way also, as the light is on despite multiple resets. The car runs fine and the sensor is seized in the downpipe so I just ignore it.

Yes, my '87 calls for 87 octane but since I had the grocery store saving and the "good stuff" was then the same price, I thought it could not hurt. Maybe it has hurt.
Now that I have a full tank, what I wonder is will the O2 light continue to trip on the next tank of 87 octane?

Maybe it is all coincidence. Maybe it is just that time for the O2 to fail.

As far a weather I have a chip, I do not think so. I have only owned the car for about 3k miles and I have not opened the ecu to check. One thing I do notice is that redline and cut-off seems to be correct at the right points on the tach. I was under the impression that most chips move redline a little higher.

jrw1621 wrote: Yes, my '87 calls for 87 octane

Huh. My '87 has a little BMW sticker on the inside of the fuel door that says 91 octane only. Silly Germans.

i just went to the driveway and on the gas door of my car is a white sticker that reads "unleaded fuel only." It makes no mention of octane.
My car's build date is 03/87

Weird. Mine is 9/87

Purported ebay chip on my ETA and I still run 87

The car has midrange power problems, but up high runs fine. (I dont think the midrange power is related to fuel)

is that octane rating RON or MON or what? I seem to remember in europe or somewhere they use a different rating, and it could say 91 there, but mean 87. or something. or i dreamed it once. i dunno

anywhooo...

ya'll do know to just buy an O2 sensor for a mustang right?

figured every e30 owner knew that one by now but only took a second to type up.

belteshazzar wrote: is that octane rating RON or MON or what? I seem to remember in europe or somewhere they use a different rating, and it could say 91 there, but mean 87. or something. or i dreamed it once. i dunno anywhooo... ya'll do know to just buy an O2 sensor for a mustang right? figured every e30 owner knew that one by now but only took a second to type up.

Europe is RON, US is PON = pump octane= (RON + MON)/2. If you check the numbers, our regular, premium, and super premium are exactly the same as Europe, as MON tends to be 10 points lower than RON.

Eric

grimmelshanks wrote: the higher the octane, the more difficult it is to burn. obvious, but it leads into other stuff i have to say. it could be that your e30 does not make high enough effective compression (go wiki the difference between effective and static compression) to burn aforementioned 93 octane. since it is not burning completely, all of that unburned fuel is going out the exhaust pipe, over the o2 sensor and it is seeing a rich condition. i dont know if your car has a modified head/deck height/piston domeage (lol i just made up a word) so i dont know what compression your car should be making, but if the cel is coming on, go back to lower octane. if that doesnt keep the light off, youre in a pickle

Oh, so not true. Dives me crazy to see this perpetuated in public formus that should be technically correct.

The higher the Octane, the more resistant it is to spontaniously break down and start a flame front that travels at the speed of sound- aka Knock. In normal burn, octane rating has no impact on burn rate at all. (actually, once the knock starts, the octane rating still has no impact on the flame front- it goes the speed of sound regardless of the fuel)

If the higher octane used had a higher content of alcohol than the car is intended to run with (since alcohol is a common and cheap way to get higher octane) THAT could be the cause of running rich or lean. It's the alcohol, then.

But gasoline to gasoline, octane has no impact on burn rate, nor does it change the nominal stoich point of the fuel.

Wait-wut? I have heard that for years. Heck, rotary racers used to try to lower the octane of their fuel because they didn't need it so high and wanted the easier to burn fuel. So their really is no difference in ease of ignition or burn indicated by octane change?

MrJoshua wrote: Wait-wut? I have heard that for years. Heck, rotary racers used to try to lower the octane of their fuel because they didn't need it so high and wanted the easier to burn fuel. So their really is no difference in ease of ignition or burn indicated by octane change?

Nope.

Ususally, you can trace problems to alcohol- which does require more energy to ignite (and more fuel to maintain proper chemistry). And historically, alcohol has been used as a cheap additive to increase octane.

but E0 to E0, they are the same.

Eric

belteshazzar wrote: ya'll do know to just buy an O2 sensor for a mustang right? figured every e30 owner knew that one by now but only took a second to type up.

As a new e30 owner, I did not know this. Thanks.
Any special year of Mustang?
Are we talking 5.0L or 4.6L V8?

I can't recall. Which ever had the same wire/wire-color combo as the one you've got. Snip off the harness, reuse the one from your old sensor, done. It's been a few years, but I seem to remember the price was around half, & a quick dyno session after the install confirmed it was correct.