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Discussion Starter · #1 ·
I have had an issue with seemingly random check engine light, car runs rough etc. Code is one or both bank max LTFT value I believe (im a dummy and forgot to screen grab). I reset the ecu using my m-engineering setup and the car runs perfect for awhile. So something is causing the car to think it needs more fuel when it doesn't

Check out this log.. note the car ran great the whole time. But it took 186sec for the alternator it seems to come on (exceed 13v) and you can see in the screen grab the voltage dropped from 14 to 13, and the o2s stopped responding.

Bad alt? very weird semi random behavior!
edit: added a view where I exaggerated
Colorfulness Rectangle Terrestrial plant Font Urban design

the scale of the battery voltage
Colorfulness Light Rectangle Slope Screenshot

Colorfulness Light Rectangle Slope Screenshot
 

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I was live logging yesterday and noticed that my battery voltage at startup was 13V which I thought was low.. I was about to measure it directly, but within a few mins it slowly went up to 14V. I thought it was odd that the alternator wasn’t driving the voltage to 14V+ at startup, but I haven’t had a chance to investigate any further (ie to check if it’s normal or not). Did you resolve your issue? If so, was it voltage related or something else?

Thanks!

Z.
 

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Discussion Starter · #3 · (Edited)
Nothing resolved yet. the slow turn on of the alternator didnt worry me too much, but is indeed odd. the weirder thing is the correlation b/w the drops in voltage and the wide bands going dead. that could be a big deal.
 
2012 MP4-12C
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Since the mid 2000's (in the case of GM, 2006) it's been common practice for basically every car to dynamically turn the alternator on and off. This reduces the load on the engine, providing better fuel economy, and strategically charges the battery to prolong lifespan. These cars are no different, they tend to take a minute or so till they kick on most times and periodically regulate up and down while driving. It should have no relationship to anything else.
 

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Discussion Starter · #5 ·
Interesting. So normal behavior. I honestly haven't noticed this before, but most the time cars I am logging im either not looking at vbatt at all, or its proEFI, Motec etc.

Have you ever noticed that the widebands go static at points during a drive?
 
2012 MP4-12C
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Interesting. So normal behavior. I honestly haven't noticed this before, but most the time cars I am logging im either not looking at vbatt at all, or its proEFI, Motec etc.

Have you ever noticed that the widebands go static at points during a drive?
I don't have a ton of experience logging like how you are, but I'd imagine with the rate that things are always changing, it shouldn't do that.
 

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Discussion Starter · #7 ·
I sent this off to m engineering as well, hopefully they have some input (it's their tune). although I doubt its tune related.

Car is so enjoyable to drive, but this seemingly random issue is getting anoying.
 
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