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7 Series - E38 (1995 - 2001)

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  #1  
Old 01-18-2013, 10:58 AM
dseemgoblue dseemgoblue is offline
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Location: Houston
 
Join Date: Sep 2010
Posts: 41
Mein Auto: 2000 740il
Engine knock with both CPS codes and Knock sensor codes

Looking for a little clarity here. I have read as much as I can on this board and others and there seems to be a number of different opinions as to how to solve.

A little history; I have a 2000 740IL and about 4 months ago a CEL popped up and I had it read and it came up CPS. The CEL came on and went off immediately and the engine seemed to be running as usual although I have always had a bit of the rough idle problem that seems to be the case with many of us. Started the car up yesterday morning and heard the " diesel engine " knocking coming from I believe bank 1 ( the right front of the engine ) and after driving the CEL came on and stayed on and the code read for a knock sensor.

The first thing I did was unplug the CPS while the car was running and there was no change in the way the car idled and when I gave it some gas it seemed to be responsive. I have read that this is a indicator that the CPS are bad and that is throwing the knock sensor fault code? Would a bad CPS cause that god awful engine knock? I have also read that there may be back pressure and that pulling the pre-cat O2 sensors and driving it around a bit? The CPS are obviously easy to replace but the knock sensors are a big pain in the rear.

Any input into steps to troubleshoot would be much appreciated.


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  #2  
Old 01-18-2013, 11:13 AM
kupplung kupplung is offline
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Location: Austin, Tx
 
Join Date: Nov 2012
Posts: 16
Mein Auto: 2009 BMW z4 sDrive35i
Are you running premium fuel? Modern engines use the knock sensors to adjust ignition timing to compensate for lower-octane fuels. That's why it says premium only, but runs fine on regular. Unless, I'm guessing, if your knock sensors go out.
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  #3  
Old 01-18-2013, 11:22 AM
dseemgoblue dseemgoblue is offline
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Location: Houston
 
Join Date: Sep 2010
Posts: 41
Mein Auto: 2000 740il
I always use Shell super premium. I also heard the you can unplug the CPS and use an OHM meter and check the resistance? I cant seem to find what the correct reading would be? I am trying to avoid doing all of the work to change the knock sensors if they are not bad. Thamks for your reply, I really do appreciate the help.
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  #4  
Old 01-18-2013, 11:31 AM
kupplung kupplung is offline
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Location: Austin, Tx
 
Join Date: Nov 2012
Posts: 16
Mein Auto: 2009 BMW z4 sDrive35i
There is a lot of discussion on whether ohm-testing the CPSs works. Those who believe it does say the correct reading should be in the hundreds of ohms, and that a bad sensor will read mega- or kilo- ohms. I have also read that the old-style sensors could be ohm-tested, but that the newer sensors on the m62tu cars can't be.

In any case, camshaft position sensors tend to fail gradually. Mine we causing a no-start without throwing any codes. If you saw CPS codes, you should go ahead and replace the sensors. From personal experience, I recommend paying the extra money for true OEM sensors.

Another test you could do, if you think the CPS is bad, is switch the CPSs on bank 1 and bank 2, and see if the knock codes switch to the other bank.
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