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Do you have a digit volt meter? Check the voltage at the jumper post located under the red plastic cover under the hood. Use the engine as ground. Check the DC voltage and then check for alternating voltage (ac).

I have a friend whose old Nissan Z was running funky. I checked the DC voltage at the under hood battery. It was all over the place. Switched my meter to read ac voltage. He had 27vac at the battery. Had to replace the alternator.

These symptoms are way whacky, basically defying logic. So, start with the basics.
 

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Discussion Starter · #23 ·
Will do now, I'm at friend's car service and we're trying all the suggestions, we'll remove the serpentine belt first and see if it changes anything. I'll keep you guys posted.
 

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Discussion Starter · #24 · (Edited)
So we figured out that alternator is self exciting. Basically the dashboard battery light didn't work, but when we tested the controlling connector of the alternator with the ground then the dashboard battery light lighted up. So technically the alternator doesn't respond to the control signal and just living by its own. I'll try replacing the alternator if we don't figure anything else.
 

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Discussion Starter · #27 ·
Disconnected the "post-cat" o2 sensors, they are suppose to be removed from the ecu but they were still sending data. No noticeable change after that. But then I disconnected the pre-cat O2s as well and I didn't get the CEL or any issue codes at all... broken ECU confirmed?
 

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Discussion Starter · #31 ·
it's very hard if not impossible to keep rising RPMs linearly until about 1200rpm, everything below this it's jumping slightly up and down, I did the best I could but it's not perfect.
 

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2003 330cic, 2003 325iT
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So we figured out that alternator is self exciting. Basically the dashboard battery light didn't work, but when we tested the controlling connector of the alternator with the ground then the dashboard battery light lighted up. So technically the alternator doesn't respond to the control signal and just living by its own. I'll try replacing the alternator if we don't figure anything else.
Just replace the voltage regulator on the back. Cheaper
 

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already did, you missed my message where i fixed it
Oops! ;)
I would focus on the cats. You did nonconventional stuff there and the highest odds are that it lead to the issue
 

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2000 E46 323i, 3.0L and 2.0L Z3's
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The logs are great. It's so nice to get clean data and not get 200 lines of data with the same data every 10 lines which comes down to 20 data points.

Both logs are good.

The MAF is under reporting 15% to20%, this causes lean conditions. I use a +/- 10% acceptable margin. So your MAF should be changed.

The total fuel trims start around 0% at idle and rise to around 10% lean at 3,000 rpm. This could be a function of the MAF error or it could indicate a fuel delivery problem. Not enough fuel getting to the rail at higher rev/fuel usage. Maybe consider replacing the Fuel pump and filter if they have not already been changed.

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I've read the thread a couple of times and reviewed the logs you have provided. Trying to see what I have missed.
  • A bouncy or surging idle is sometimes caused by a vacuum leak. On the M54 engines, it can be the loss of the blanking cap on the small nipple on in the middle of the CCV regulator. You have the M56 valve cover, so it's different. I know nothing about the M56 system as they never made it to my part of the world.
  • One of your logs showed an extremely rich condition, the other a slightly lean condition. The rev-rise logs, show a lean condition. What ever the problem is, it is common to both banks.
  • All I can suggest, is to have a good look at the M56 valve cover installation. Are there any vacuum leaks or ways for oil to be drawn into the inlet manifold to provide extra fuel and cause the rich conditions. Maybe check that the oil drain tube inside the dipstick tube is clear?
That's about all I've got. Good luck with the search.
 

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Discussion Starter · #40 ·
Thank you very much, I will report my findings here.
M56 valve cover is almost identical to M54, the only difference except the material is the PCV location and newer type of coils, also the gasket is a bit different. We don't have them here as well, I bought it on ebay from California. There are no vacuum leaks, at least no significant ones, I recently noticed my valve cover gasket started leaking since I was removing valve cover when fixing VANOS seals and used old gasket to put it back on (need to order gasket from EU for m56). Hovewer the caps on the back are all there, I was removing those caps before to create intentional vacuum leak because it was driving better this way but for some reason it doesn't do it anymore so I put them back. So I'll need to replace the valve cover gasket, maybe oil is spilling somewhere. Also my fuel consumption is just ridiculous the last few days, it's 19.3L / 100km, all a did was play with the o2 sensors configuration, but now first o2s are connected and second o2 are disconnected and the consumption is still ridiculous...
 
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