slow acceleration problem....o2 sensors? - Mercedes-Benz Forum
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post #1 of 38 (permalink) Old 07-17-2008, 12:06 AM Thread Starter
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slow acceleration problem....o2 sensors?

Hi everyone, I always feel that my car has slower acceleration time (0-60) then a lot of you guys did on the forum....I replaced my MAF about 2 months ago then dis/reconnect the battery, feels much quicker but only last for about 2 weeks then it gets slower again. I tried to do the reset ECU thing and doesnt feel quicker. Last week the check engine light came on and mechanic saids is the O2 sensor problem. I didn't replace it yet and I just dis/reconnect the battery and clear the light. The car is back to quick again. So if I replace the O2 sensor will the car be quick like right after I disconnect and reconnect the battery all the time without dis/reconnect battery every like 2 weeks? or is there some other reason that the car only gives the quick performace after dis/reconnecting battery? Is a 2000 E55 with 110000km on the car now.....no mods except for the x-pipe. Thanks!
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post #2 of 38 (permalink) Old 07-17-2008, 05:58 AM
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i would suggest replacing the o2's as soon as possible. you risk running overly rich or overly lean for an extended period of time. this is not only bad for your gas bill but could harm other parts of your car or motor depending on which condition you are suffering from. Sounds like you are running too rich, how bad is your gas mileage when the car is "not quick"?
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post #3 of 38 (permalink) Old 07-17-2008, 10:18 AM Thread Starter
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the millage I get is about 18-20L/100km city driving (I am in canada so the display is set on metric) and highway about 14-15L/100km....is it more gas usage then normal?
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post #4 of 38 (permalink) Old 07-19-2008, 12:35 PM
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"I replaced my MAF about 2 months ago then dis/reconnect the battery, feels much quicker but only last for about 2 weeks then it gets slower again. I tried to do the reset ECU thing and doesnt feel quicker."

I have the exact same situation. I replaced my MAF with one I bought from Autohauz AZ and disconnected the battery overnight. Next AM the performance was fantastic! The car absolutely jumped from 60 to 120mph in what felt like 8 seconds. It would spin the tires when rolling at 10mph and flooring the throttle. Just incredible. That lasts about a week and then it's kind of doggy again. Floor it on the highway and it downshifts but doesn't jump up and leap forward, just more engine noise and moderate acceleration. I disconnect the batter overnight and it restores the power again.
I had the drivers side catalytic converter replaced and just had the passenger side checked and it is fine. No codes. Just had my MB tech friend hook it up to the dealers Star diagnostic machine and all the values are spot on.
As much as I love the car I am growing weary of this hit or miss performance. I call it the "Forest Gump E55", it's like a box of chocolates, you never know what you're going to get when you step on the gas! I don't drive aggressively all the time so perhaps the "adaptive" transmisison or ECU is punishing me. I'm not sure if this is acceptable behavior and am considering moving on to another vehicle. Perhaps something with fewer computer controlling issues. Maybe these aftermarket Bosch MAF's are junk? I know they are not remanufactured but my MB tech (18 years experience) said he doesn't trust the ones bought aftermarket. I explained that Bosch is Bosch but he seems to feel the MB has them built differently than the generic Bosch MAF's that fit many applications with one part number. I don't want to pop $350.00 at the dealer just to have the same results. Any thoughts?
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post #5 of 38 (permalink) Old 07-19-2008, 01:00 PM
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Originally Posted by MaxVon View Post
...Maybe these aftermarket Bosch MAF's are junk? I know they are not remanufactured but my MB tech (18 years experience) said he doesn't trust the ones bought aftermarket. I explained that Bosch is Bosch but he seems to feel the MB has them built differently than the generic Bosch MAF's that fit many applications with one part number. I don't want to pop $350.00 at the dealer just to have the same results. Any thoughts?
This has been debated before and a lot of people feel the same way your MB tech does. I have also seen at least one very knowledgeable member on here argue that "Bosch is Bosch". I really don't know but I have never heard anything negative on here about autohaus.az. If they sell a part as OEM, then I believe them. The alternate brands they also offer might be questionable.

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post #6 of 38 (permalink) Old 07-19-2008, 01:17 PM
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Post MAF's an O2 Sensors

You guys are likely suffering from Computer problems brought on originally by a bad MAF. When the MAF goes out it will often throw O2 codes because it can make the cars run rich and ruin the O2 Sensors. The O2 in turn will also screw with the Computer and jack up the mixture programming. Equals bad performace and bad fuel economy. When you reset the Computer it goes into a preset default mode till it has a chance to read the cars sensors. This will take a number of start/stop cycles. Hence your smoke the tires performance after resetting the computer. Once you understand the system and how they work Forrest Gump will be taking a back seat on the bus, If it ever shows up.

Good Luck!

C as in 220
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post #7 of 38 (permalink) Old 07-19-2008, 01:34 PM
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Originally Posted by cjshade View Post
You guys are likely suffering from Computer problems brought on originally by a bad MAF. When the MAF goes out it will often throw O2 codes because it can make the cars run rich and ruin the O2 Sensors. The O2 in turn will also screw with the Computer and jack up the mixture programming. Equals bad performace and bad fuel economy. When you reset the Computer it goes into a preset default mode till it has a chance to read the cars sensors. This will take a number of start/stop cycles. Hence your smoke the tires performance after resetting the computer. Once you understand the system and how they work Forrest Gump will be taking a back seat on the bus, If it ever shows up.

Good Luck!

C as in 220
I appreciate the responses. I still don't "get it". All values for 02 sensors, MAF, Air to Fuel ratio where spot on according to the Mercedes Star diagnostic tool. So if the values are correct, how can the computer keep messing up the mixture program? Very frustrating to know all that potential is there and not being able to use it.
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post #8 of 38 (permalink) Old 07-19-2008, 01:42 PM
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Post Ask the shop

I would ask the shop what's the deal that the default learn mode is performing better than normal run mode when no codes are present? The only other thing I might add is MAF's can be bad and NOT CODE. My car got to where it seemed like it was running on 2 cylinders from a bad MAF and NO CODE! Try disconnecting the MAF and run in default mode. See if the performance improves right away. You may have a bad new one. It's rare but I have heard of it happenng.

Good Luck!

C as in 220
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post #9 of 38 (permalink) Old 07-19-2008, 01:47 PM
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Originally Posted by Musikmann View Post
This has been debated before and a lot of people feel the same way your MB tech does. I have also seen at least one very knowledgeable member on here argue that "Bosch is Bosch". I really don't know but I have never heard anything negative on here about autohaus.az. If they sell a part as OEM, then I believe them. The alternate brands they also offer might be questionable.
Hello Musikmann,

On the "Bosch is Bosch" issue, yes I agree that the parts Autohauz.az sells are genuine Bosch items in a Bosch box with Bosch part numbers. The issue my tech brought up is that the part Autohauz sells from a Bosch parts distributor is made for many different automotive applications. It may fit our E55's as well as a 2005 BMW 5 series. He theory is that MB makes a dedicated part for the their cars with certain tweeks that are recognized by the ECU and where a generic Bosch part will not have that tweek and affect performance. When I had the OEM MAF when living in CA the car ran like a beast all the time. Only when I moved to Boston and had a catalytic converter go bad then the MAF go south have I had this issue...
I'll see I can find an O.E.M. MAF at a bone yard and try that maybe?
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post #10 of 38 (permalink) Old 07-20-2008, 06:31 PM Thread Starter
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so the best solution is to go for the MAF from dealer? or changing the O2 sensor will help? I have already ordered the O2 sensors it should be on the way.....hopefully it will really help. btw before I got the new MAF 2 months ago I cleaned my original one and then the car runs like as it should too (very powerful)....then I got the new one that I have now after a couple of weeks and before that the "cleaned" old sensor is still doing great....maybe I should put that back on? or maybe I should just disconnect the battery at nite and reconnect back every morning =D

Last edited by msiumng; 07-20-2008 at 06:44 PM.
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