MAF sensor question
 

Lost power on my X. The feeling was like I'm driving 3.0 instead of 4.4 .
Later, I found out that MAF sensor was the problem, and when I disconnected it , the car was alive again. Now the question is if I will be driving with disconnected MAF, until I will get a new one, may it cause any other problems or no? Will it damage oxygen sensor? :dunno:
THank you.

I can't answer this with authority because I'm not educated in the matter. However logic would tell me that the purpose of the MAF is to help ensure complete combustion of the fuel/air mixture by measuring the air volume taken into the engine and adjusting the fuel and timing accordingly. Without the MAF the air is unmetered so the engines brain can't tell what is the correct amount of fuel to inject or where it's at with timing. The result is a less than ideal burn cycle and following on from that will be less than ideal exhaust gas. I'd imagine the O2 sensors and the cat are probably not designed to cope with that and are likely to suffer as a result.

But two things.

One is that if your MAF has been bad for some time then the fuel/air and timing have been off for some time also. That being the case, I wouldn't have thought that unplugging the MAF would have a significantly detrimental effect for the while that you're waiting to install a new one.

And second, I can't imagine the replacement part will take that long for you to get ? So I'd say for a short time you shouldn't do any material damage to O2 sensors or cat.

I suspect I have a similar issue. I've been trying to track down the reason for this annoying power loss I've got between 1,000 and 2,000 RPM for some time now. Thing is that you could spend thousands replacing this and that part without solving the problem so I've been trying to learn more of the characteristics of the symptom before I go in a particular direction. My MAF is on my radar as a possible culprit ..... think I'll try disconnecting it one of these days and see what happens.

"Thing is that you could spend thousands replacing this and that part without solving the problem so I've been trying to learn more of the characteristics of the symptom before I go in a particular direction." - Agree 100% !!!
I went through a lots of forums and 90% of people were saying that if you unplug the MAF and the power comes back the MAf sensor is the problem. So, I ordered today a new MAF sensor from Autozone. Its Cardone reman sensor - 286$ plus tax with one year warranty and 90 days return option. I'm going to try it. If its not good I will return it. I know that it is possible to get this sensor for 50 or 60$ less on the ebay or amazon but I dont want to take that risk.
Estimated arrival date 7/6/11. I will post the results when will get and install it.

You may want to read this post for an explanation on MAF sensors:
How to test the MAFs yourself and How MAFs work - The Unofficial BMW M5 Messageboard (m5board.com)
The e39 predates the e53 but I suspect much of the same engineering principles apply to both. In a nutshell, the engine computer can estimate the air flow from the other sensors so if your MAF sensor is shot, the estimate will be better than the shot readings hence better performance. You can also try cleaning them but this is, apparently, only a temporary solution.

I tried to clean the MAF before I ordered a new sensor. I used CRC Mass Air Flow Sensor Cleaner but it didn't give any improvements. Thank you for the link. It says in there that MAFs typically last 50000 miles before getting so contaminated it affects engine performance. My MAF has 46000 miles on it.I guess its time for a new one.

No problem, you're welcome. Some people change out these consumable parts on a regular basis as preventative medicine. Do you have a code reader? It would be helpful to know if it is throwing any codes.

No I don't have a code reader but I'm sure that I should get one. I'm probably gonna have to do a research on that in order to find out which one I should get.
In my case everything started with the check engine light and significant decrease in engine power . I disconnected the battery for about 10 min and when I connected battery back the check engine light never came back again, no matter if the MAF was connected or disconnected.

FWIW, I have a Peake code reader and it's good for basic codes on the BMWs, mainly emissions related codes. It seems to be the staple for many of the older vehicles. There's quite a bit of help at the M5 forum I go to. Very simple to use and would probably get the codes that gave you your check engine light. It will also reset oil, service intervals, and clear codes.
Products
I also just ordered this software:
BMW GT1 Software
It's supposed to replicate the GT1 system dealers use but I won't know till it arrives and I can play with it.

Finally got the new sensor with the core yesterday. Plugged it and ..... it's working perfect.
No check engine light and power is back. I'm back on the road.

Excellent result, well done.

A little update. After I drove the car for about 50 miles the check engine light came back. My friend explained me that after I disconnected the battery I didn't drive it long enough and that is why the check engine light never came back. Now the check engine light is on because the old error was stored in the memory and it need to be cleared. So, I purchased today actron cp 9575 autoscanner. After a scan I got p0171 and p0174 codes.
A code P0171 and P0174 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty.
There could be a vacuum leak downstream of the MAF sensor.
I made a reset and cleared all the codes that were stored. After that I tested and drove the car for a long distances. All's clear. The check engine never came back again.

Way to go!:thumbup:

Did you get the GT1 software?

It's still in transit from the other side of the pond. Once it arrives, I'll also need some time to get it working on an old laptop of mine. Lastly, I have a tendency to blow things up so please bear with me and I'll keep you posted.

So where did you end up ordering the sensor from ?

I purchased the scanner and sensor from Autozone.