UPDATE: I think I figured out the problem. It was the O2 sensors that kept on messing with the long term fuel trim overriding even the open loop mode. I have an obd2 reader where i can graph simultaneously the output of both front 02 sensors, right away from the graph i could tell o2s were stalling at times and one was more active than the other. New ones are on the way. and for Now I disconnected both front o2 sensors and to my surprise no check engine light. I graphed the outputs of o2's now and they are at constant .48v on both which makes the ecu no to interfere with long or short fuel trim,, weird//
Car pulls like a beast and not slowing down with both o2 disconnected.

 

Interesting... good work troubleshooting

Report back once you receive/install O2 Sensors

 

Hmmm... so we can drive with our o2 sensors disconnected? I'm going to try it...

 

Very interesting. I'll be curious to see the results. How many miles on your E55?

 

106,000

 

Hrmm might have to try this

 

Update: ok check engine light did come on today, but car drives the same no slowing down and this might sounds strange but transmission shifts instantly as if the car has been just reset. So a bad o2 sensor will screw up power and will make the transmission lag? weirdness ..
also my MPG went up by 2 mi in the the city from 15.5 to 18 ,
I'm just wondering now if it was a good idea to get Bosch o2 sensors since both MAF and o2 are made by them and seem to be a common failure on these cars.

 

Can we unplug the o2 sensor by hand? Or we need tools? More information would be appreciated.

 

You can unplug them by hand or with help of flat head screw driver. Open your hood and on both sides close to firewall you will see blue wire and the connector is right there, very easy. 02 sensors are on top of the manifold.
After you unplug them make sure you disconnect the battery for 1 minute or so to reset the ecu's previous settings learned from 02 .
Post back the results.

 

Buahahah... I'll peek in either Friday or Saturday.

 

Any update? Have you replaced your 02 sensors yet?

 

Replaced the O2 Sensors (front only, since I think rear have no effect on fuel trim. or do they?) and reset the ecu, at first I thought problem was cured but after about 5 days again back to square one with power loss, although I should mention that I think power loss was not as dramatic as before and it also took a little longer for ecu to tune power down.
So in search of an answer for this problem I ended replacing oil one more time after only 2000mi on old oil and to my surprise it cured 80% of the ticking(lifter noise) that I had. So this made me think there was really lots of gunk build up inside the engine from previous owner which could in turn could cause high compression and when knock sensors would sense any detonation, timing would be turned down causing power loss. BUT why with o2 disconnected there is no power loss at all? If it was related to knock sensors than disconnecting 02 would have no effect on this would it?
I have to confirm no power loss yet,
to be continued.....

 

any updates on this? My car is feeling the same and I am thinking new MAF and O2 sensors. I am going to get the oil changed this week, so that might help. Also i'll try resetting the ecu.

 

That is sport mode. If you slam the pedal and then release it the car stays in the low gear anticipating that you are going to slam the pedal again.

 

hi guys! how do you disconnect the battery? thanks!

 

On each side of the rear seat, you can stick your hand under and feel a latch. Pull that, and the seat will pop up. You'll find the battery underneath.

 

Update:
after replacing front o2 sensors, 2 new MAF, spark plug wires and spark plugs the issue still remains, although power loss is not as dramatic as it was before.
After resetting ecu by battery disconnect car runs great for around 4-5 days and than power loss creeps in, quarter mile trap speed drops to 104mph after power loss vs 108mph after reset.
And it has nothing to do with driving slow and ECU readjusting to granny mode, no matter how I will drive power loss always comes back.
The only method I have found to cure the power loss is to disconnect two front o2 sensors completely and by this overriding fuel trim correction which contributes loss of power, car will run constantly in Open loop but Im not sure that it is safe to run the vehicle this way all the time (please correct me if Im wrong)
I don't know where else to look and what else to try.
maybe a dyno with AF reader will tell me a little bit, at least what is going on with my AF ratios when power is down.

Lets get this problem figured out guys. Please provide any valuable input.
Thanks

 

Hello, I just picked up an E55 about 3 days ago. And I am having the same problem as you. Im thinking about pulling the plug on the o2 sensors. I know that you said that the CEL comes on, But will they go away once plugged back in?

Thanks in advance. BTW this was the car that I just picked up.

http://www.benzworld.org/forums/sale...low-miles.html

 

Yea they go away after being reconencted. Have you tried new MAF yet? If not, its the first thing I would try. I have Brand new Bosch insert for $100 if you want to try that first.
Unfortunatly for me the problem still persists after 4 new MAF , new o2, new wires,.. Its driving me crazy,, I think maybe there is a glitch in the ECU itself

 

I must add Alex that you're not the only one with this problem. When one of my relatives got their W210 E55 gosh, 7 years ago and took me for a drive, all I could feel was huge low end torque. After I got my license and took it for a spin, all that torque and power was gone and I swear it was just as fast as my now gone E320. I had just driven a W140 S600 that day which has more power and torque than an E55, but is slower than an E55 because of it's weight. I was pretty confused about why it felt so slow!

 

I think its ECU related, bad programming from the factory. Its just stupid for the ecu to pull -25% of fuel at wot or at higher loads when O2s clearly show that Engine is running lean,,something is defently mest up here since any half smart ECU would throw a code to indicate that there is somthing wrong or start putting back fuel not subtract it...........

Im also thinking that all that lean running has to be bad for the engines internals.... I might as well just disconect the O2 and forget fuel corections all together , restore lost power and will be running slighly richer and safer for the engine...

 

Hey Bud!

You know we all had this debate a few times. The ECU is horsecrap! Once n while I'll just do the ECU reset to get her fired up again. But nothing like when you disconnect the battery and take her for a spin... Insane Night/Day. I don't think I feel it as much with my mods, well at least when she starts to get a little sluggish the easy ECU trick works for me. (you will notice when in traffic and lots of stop/go she slows down after a week) give or take. For me anyway.

Armani

*** I hear ya.. pretty annoying if you ask me

 

I always have nitrod in my dash so i can monitor fuel trim and all the data,, Sometimes driving the car just for half a day even will get -20hp because of the ecu being retarded, sometimes it takes a few days but in my car at least, after a week of driving im in the e320 teritory,,its bad.. and its bad for our engines because of fuel starvation at top end....
I actually googled Ecu Failures in w210 and it looks like its a common issue and is also related to the rough idle that so many of us expirience...
Fudge,, at times like these i wished i have gotten a lexus,,....

 

So I did a little more reading.. and came across this, I doubt you have a bad ECU unit but in either case it probably adapts quicker when driving slow. Although I can't confirm that just a guess.

Armani


The following has been drawn from my involvement with Bosch ECU’s (Motronic) found amongst others, in the BMW cars and motorbikes. The object of this document is to provide the vehicle owner with a simplistic but relatively accurate view of what is taking place during ECU reset function.

What’s with the ECU?
One thing about ECU’s is that although basic in execution they posses the ability to process a large number of inputs in a relative short span of time rendering a predetermined range of outputs.

Most of the current ECU’s have some level of learning built in, basically, this is done to allow the ECU to adjust certain parameters to the driving habits of the owners. Albeit a positive thing to have, since it will collect/update the stored information based on the various driving conditions it encounters, it sometimes works in a negative fashion when the car is subjected to a steady diet of stop and go traffic.

After the ECU has been reset it adopts a base factory setting. In my car, a 99 E430, the shift points occur at 2400 rpm, after reset, under moderate acceleration. Every ignition On/Off is considered a cycle and the computer will average 10 cycles and adjust the parameters accordingly.

Another parameter that is reset is the A/F ratio for the base map, this ratio returns to a slightly richer one, once again as the vehicle enters the closed loop operation (steady state, constant power conditions, where the mixture is governed by the O2 sensor output) the A/F ratio will change accordingly, most of the time to a leaner condition where mileage can improve at the expense of a slight loss in power.

If the owner becomes significantly more aggressive in their driving the cycle repeats itself with the associated results, it stands to reason that if the driving style decreases so will the performance of the car. (i.e. shift points). Do remember that at this point you are working with an average and even in the case of a major change in driving style, either way, will result in a small overall change as it is being averaged. (Sum/10). One way to get around this fairly quickly and start afresh is by resetting the ECU.

Procedure to reset the ECU
Ignition to #2 position, dash on engine off
Depress accelerator to the floor and hold there for a few seconds
Release accelerator
Turn ignition off
Wait 30 seconds

BTW, this is equally applicable to all Bosch equipped Motronic systems.

How often should you reset the ECU?
This is based on your driving habits. In my case I drive a little in the city, but most of my driving is at highway speeds, at slightly above posted limits. In my case I reset the ECU after 3 months running. On the other hand, someone that encounters bumper to bumper traffic everyday it might be advantageous to reset more often.

 

Interesting info about this car's ECU. I took it out for a spin yesterday and it had its low end grunt back, but I did notice again that power tapers off at higher RPM.