BMW Werkz banner

1 - 20 of 24 Posts

·
Registered
Joined
·
31 Posts
Discussion Starter #1
My check engine light popped up the other day....90k miles ... seems like the common reason for the check engine light coming on is due to a bad 02 sensor. But can this cause a loss in power? My acceleration is not what it used to be. Thanks for the feedback.
 

·
Registered
Joined
·
5,973 Posts
the o2 sensor shouldnt cause a noticiable drop in power, but im not sure. Loss of power is usually the result of engine compression loss or a dead cylinder.
 

·
Registered
Joined
·
698 Posts
A faulty O2 sensor can do many higns to your car and poor performance could be one thing. The O2 sensor sends bad info to the ecu and you air/fuel ratios are screwed up, very likely problem.
 

·
Registered
Joined
·
497 Posts
I would have the fault codes checked. Especially with 90K on the odometer. I would suspect a clogged catalytic converter.
 

·
Registered
Joined
·
497 Posts
..and by the way, I would also replace the O2 sensor as well.
 

·
ex owner/admin
Joined
·
10,839 Posts
Originally posted by pooskay@Dec 15 2003, 08:12 AM
My check engine light popped up the other day....90k miles ... seems like the common reason for the check engine light coming on is due to a bad 02 sensor. But can this cause a loss in power? My acceleration is not what it used to be. Thanks for the feedback.
it will affect power because the car is essentially running in safe mode (like a computer sort of) because the signal is bad to the DME the car runs the car in a sort of "safe mode" where the car purposely dumps more fuel into the car then normal to compensate for any possible situation that the car could run without the readings of the O2 sensor. this is why its typical to notice poor fuel mileage and somewhat poor performance .
 

·
Registered
Joined
·
497 Posts
Have you noticed any rotten smell from the car/exhaust, like a rotten egg or sulfur smell?
 

·
Registered
Joined
·
31 Posts
Discussion Starter #12
no, but its giving off a very heavy fuel smell when i start it up....a couple times when i started my car (cold start), the engine shook/vibrated for about 5 seconds and struggled to reach a stable rpm..seemed like it was going to shut down, but never did.... but that only happened twice out of many starts.
 

·
Registered
Joined
·
497 Posts
See this is where it can get costly and difficult because while the 02 sensor is a likely cause, there are also many other possibilities that lurk. Another possibility is the crankcase vent valve or any type of vac. leak. The fuel smell could be because of either. If there is a vacuum leak or a bad maf (any type of lean condition) then the DME is going to correct this by dumping more fuel which will cause the 02 sensor to go frantic. Same possibility with a coolant temp sensor. All the added fuel will then create the fuel smell. However, a bad catalytic converter can do the same just in a slightly different fashion. I could go on and on, just too hard to quickly diagnose the problems that you're having without fault codes.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #14
well i took it to my mechanic and he got an "undefined" code. ill probably take it to a bmw shop next time....thanks again for the info!
 

·
Registered
Joined
·
497 Posts
undefined meaning what? did it just say "undefined" or was there anything else along with it??
 

·
Registered
Joined
·
31 Posts
Discussion Starter #16
and bmw shop looked at my car before regarding the fuel smell. they said my secondary air pump and fuel valve needed to be replaced. havent replaced it yet cuz they're charging 600 somethin $$ , and because the sec air pump only functions at startup for the first couple minutes or so....correct??
 

·
Registered
Joined
·
31 Posts
Discussion Starter #17
Originally posted by EXtech@Dec 16 2003, 06:08 AM
undefined meaning what? did it just say "undefined" or was there anything else along with it??
from what i remember, he just said "undefined" ...maybe he screwed up ?
 

·
Registered
Joined
·
497 Posts
Here in lies the problem... possibly. True about the secondary air pump. However, the purpose of the secondary air pump is to pump air into the raw unspent gases to reduce emissions. By not doing this at all or not enough, the O2 senor is seing far too much raw fuel which can ruin the O2/fail premature and even destroy the catalytic converter. The DME is programmed for specific parameters and everything is designed to work as a system. Basically the O2 is looking for a preset range of A/F ratios and CO2 content and not seeing it. This would possibly explain the "undefined" code because that diagnostic may be too complex for your tech's diagnostic tool. Now, I am not saying for sure that this is your problem but it would be highly suspected.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #19
hmmm sounds very logical and VERY possible...i will take it in for a second opinion, and i'll have your explanation in mind ...thanks a lot.

hopefully replacing the secondary air pump w/fuel valve and 02 sensor will solve my problems, cuz i miss the power i used to have! spark plugs and air filter are new..hope its not a vac leak.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #20
well i promised an update on this issue.... and Extech...you were right....the cause of the check engine light was due to a bad secondary air pump! the O2 sensor appears to be fine....bro is still working on replacing the air pump + check valve..so we'll see if it affects the performance, but i doubt it, cuz i've read the secondary air pump does not have anything to do with performance...is this correct?
 
1 - 20 of 24 Posts
Top