Bank1 unstable fuel trim
 

I'm trying to chase down the cause of my unstable Bank1. Bank2 looks stable.

I recently just put in a replacment engine. engine starts up every time, and idles fine, it runs very rich at idle. No CEL at all also.

I'm on the same tune as my previous engine, and have added headers now.

Things I have done:
-smoke tested the intakes and plenum for leaks. Everything mostly checks out, I do have some smoke coming from the maf from both bank1 and bank2. i plan to swap the maf from bank1 to bank 2 and make sure the seal is in good condition or replace it with a new one. Voltage for both MAFs are also consistent which makes me believ eits not the MAFs.

-Had an exhaust manifold leak and replaced the gasket. but problem still exist. made sure the test pipe to header flanges didn't have leaks and rtv them to make sure.

-replaced the spark plugs with new oem. swapped igition coils from bank 1 to bank 2 and still same problem.

-replaced the pcv valve

Next things I plan to do:
-swap the upstream o2 sensor. these are new Denso sensors also, but will swap bank1 to bank2 to see if the problem follows

-pull the fuel injectors to check o-ring and swap bank 1 to bank 2 also. injecors were sent off to be cleaned not long ago.

-read somewhere that the downstream o2 sensor somewhat sends a feedback signal and was a cause of some people's bank issue. I have test pipes with defoulers and have never had any problems previously. I will unplug them and see if it affects anything.

I can't think of anything else

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Update:

Swap bank1 and 2 MAF = no fix

Pulled injectors and swap bank 1 to bank 2 = no fix

No tested bank 1 exhaust side but didn't see any leaks at the test-header flange or header-block flange

swapped the upstream o2 sensor but haven't started up the car to check.

not sure what else I can do after this.

How rich are you running at idle? You may need to re tune.

What do your AFRs look like when you do a pull to redline? The ECU will go into open-loop mode which ignores the short term fuel trims (they should read 100% during this time).

Have a tune session planned but can't tune until I have this resolved.

my bank 2 will sit at 97, but my bank 1 will jump between 100 and 125.

at idle my AFR for bank 2 is around 14.7 and my bank 1 will jump around from 12s-16s.

Could you post a log file?

updated the original post with more information

Did you do any kind of mechanical engine checks? Compression, leak down? Sounds like you’ve done all the control side stuff swapping but you say it’s happening after an engine swap. What’s the condition of the engine? If your having a bad or weak cylinder it’s going to show more at idle than at higher RPM. I’d suspect it to have to be pretty bad to throw off the fuel trims that much and would show more running condition issues (misfire etc) but as you’ve already done all the injectors which would be the only other main thing aside from a shorted harness which again should massively show an issue.

I haven't done a compression or leak down test. I can do a compression test next, just to confirm. The engine is a low mileage engine I got locally, 15,000 miles from a reputable shop, so I didn't think about a weak cylinder at first.

I forgot to mention, I swapped the O2 sensor (upstream) and the fuel trim seems to not be as erratic, bank1 in the 90s-100, and bank2 80s-90s.
O2 sensors were new when i installed them.

UPDATE!

I finally found the issue that was causing my problems.

I had the plugs for the ignition coils for cylinder 3 and 5 mixed up.

I couldn’t find a wiring diagram for VHR harness so I use a DE as reference.
Sure enough, it matched.

When I was plugging everything up, I thought the lengths were obvious enough to determine which cylinder they went to.

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