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engine running rich

15K views 21 replies 6 participants last post by  Dionte 
#1 ·
My 95 540i is running rich there is fuel smell coming from the exhaust. The check engine light comes on and goes off its intermittent. I am wondering if an O2 sensor would cause this? I am new to bmw is there a way to check the computer codes?
 
#2 ·
Sounds like you are on the right track. You can do a procedure called the stomp test. Either search here or google it as it is a little long winded to explain it here. Basically it is a way to trigger the on board diagnostic computer to display any error codes using a series of flashes of the CEL light on the dash.

Let us know what you find.

Steve
 
#4 ·
Have you downloaded the bentley manual? It has all the troubleshooting, diagnosis and fixup steps that you need to follow in this situation. Search these forums for the download link. Good luck and let us know how it goes.
 
#5 ·
I have the bentley manual it really doesn't say much about rich fuel mixture. I looked for vacum leaks but I couldn't find any. the engine has 193,000 I dought any O2 sensors have been replaced. would a faulty O2 sensor cause a rich mixture or could it be a bad mass air flow sensor?
 
#6 ·
BMW recommends replacing the O2 sensors about every 50-100K miles (I can't remember which). Anyway, you should replace both O2 sensors, especially since you have an error code for it and you have so many miles. Bad O2 sensors will definitely screw with how your engine runs. The E34 only has a pre-cat, two in your case since it is a V8. It's an easy DIY on the 6 cylinders, probably not too bad on the V8. I would not look at the MAF (unknown if it is a problem) until you replace the O@ sensors (known problem). Plus, if the MAF was bad, you would likely get an error code for that as well.

Good luck.

Steve
 
#9 ·
Eagerly awaiting results :)

And yes, there are a total of only 2 O2 sensors on your car, one on each exhaust prior to the catalytic converter.
 
#10 ·
O2 sensors

I got to looking and I think I might have ordered the wrong O2 sensors the part numbers I ordered are bosch 13523 and bosch 13522. I only see two sensors located on each of the exhaust down pipes? I don't see any after the catalytic converter anyone know if these are the correct sensors? it looks like the wiring connector on bosch 13522 is different than 13523. its a 95 540i I am wanting to replace all O2 sensors on the car
 
#12 ·
I got to looking and I think I might have ordered the wrong O2 sensors the part numbers I ordered are bosch 13523 and bosch 13522. I only see two sensors located on each of the exhaust down pipes? I don't see any after the catalytic converter anyone know if these are the correct sensors? it looks like the wiring connector on bosch 13522 is different than 13523. its a 95 540i I am wanting to replace all O2 sensors on the car
ahults, as said before, there are only 2 sensors on your car. One on each downpipe as you stated. It is an OBDI car that does not use post cat sensors.
 
#13 ·
Dude, just had an idea. Disconnect the existing o2 sensors...just unplug the sockets from the wiring harness. The car will switch immediately to stored factory values....a backup typical map. This will not be as perfect as working o2 sensors, but will also not lead to running rich condition and you can drive your car comfortably. When you get the new sensors, you can fix them in and reconnect the sockets.
 
#22 ·
I wouldn't doubt it. Had the same issue on my 535i. Used to idle up and down and get terrible gas milage and it also had a bad fuel smell. After I got a new o2 sensor, gas mileage increased, fuel smell went away, idled normal and steady and it restored my throttle response.

Did you pull any codes?

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