So I should unplug both o2 sensors and see if computer goes back to normal fuel readings?
Yes , it wonât run correctly but it should even both banks up an show the rest of the system is good. If it doesnât itâs most likely the DME
Ok thank you I will try it
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I unplugged both the upstream o2 sensors and car still has hesitation. When they were unplugged all fuel trim were showing %0 . O2 sensors were showing 0.074 mA. Does this mean computer still thinks O2 sensors are connected?
When I plugged O2 sensors back in fuel trims all looked good except for long term fuel trim bank 1 was constantly over %10
As long as both banks even up it shows the DME is defaulting correctly . The long term view may take a while to come right depending on what system youâre testing with, if you can reset the adaptions plug everything back in and watch your injector open times they should adjust at a similar rate , if not as youâve done O2 sensors itâs looking like the DME is faulting, may be worth getting it reprogrammed or looked at by an electronic repair shop
Thatâs good info. Presumably fuel rail shares both banks, so unlikely to be a problem with fuel rail pressure. & unlikely to be leaking injector, b/c all three on that bank would be to be faulty. hmmm ⊠Iâm guessing in order of likelihood the explanations are
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intake air leaks (intake manifold/throttle-body gaskets, rubber intake-path boots past the MAF, pcv system air leak for that bank, etc) are allowing unmetered air into combustion chamber.
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exhaust system air leaks for that bank are allowing outside air to come in contact with o2 sensor
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o2 sensor for that bank, associated o2 sensor circuit wiring, or ecm problem.
Until the rich mixture problem is solved, might be a good idea to remove the new cat you installed, put old one back, otherwise risk having to install another new cat.
For addâl clue, might be a good idea to ask shop to assess the fuel injector electrical-pulsing situation, comparing bank 1 to bank 2.
Would you suggest sending the dme to one of those dme service repair on eBay?
Iâve worked for BMW for twenty odd year and to be honest itâs luck of the draw, repairing the outputs for the coils or injectors seem fairly doable but when youâre into the sensor interpretations thatâs pretty hit and miss. Second hand ecus are a problem because they contain the chassis number which requires after market software 
And Iâve seen newish cars wrecked because itâs wiped the vin number from the whole car.
Do you think it is possible for bad valve cover gasket to cause bank 1 lean code?
Seems unlikely. If outside air leaked into valve cover , it could get into the pcv system, from that sucked into engine air intake. But that would affect both banks, not just bank 1. I suppose if the valve stem seals were dodgy, that could cause air under the valve cover to get sucked into combustion chambers, affecting only that bank. Is there any indication the valve stem seals are leaking? Cloud of blue smoke out the tailpipe when first starting engine after it has been sitting for an hour or two?
Might be intake manifold gasket
No blue smoke. The car doesnât smoke.
I have a feeling the problem could be some gasket cause an air leak. These German rubber go bad at high mileage
A faulty one of those could cause a lean code. Depending on engine configuration, it might only show up in one bank. No experience w/your car or engne. Is it a V 6 or V8? Is it turbo- or super-charged?
Itâs 6 cylinder twin turbo
V6 or in-line 6?
Inline 6 cyl
Thereâs actually a poster here w/handle @TwinTurbo . Maybe theyâll chime in on this one.
That new catalytic converter cost me $1600. Real slap in the face. That one guy was right about not swapping it out. Could be something as little as a gasket