u/rhodesman

have a thread going with my friends and thought it would be fun for people to share what they drove back when the movie first came out

Context:

This issue is for a 2010 135i w/ N54 engine. This is a fully built engine with pistons, rods, racing bearings, still TT but upgraded. Still using the BMW plastic valve cover but I have a BMS PCV valve and every gasket, seal, etc. was replaced ~3,000 miles ago. I've done smoke tests on the vacuum system, intakes, valve cover and there are zero issues there.

The 29E1 error ONLY happens after about 10-15 minutes of the car starting, if I clear the code it wont come back until I turn off the car and start it again and then, again, 10-15 minutes after starting it will come back.

Symptoms

• Code 29E1 (Fuel Mixture Control 2 / Bank 2 fuel trim range exceeded)
• Triggers after 10-15 minutes of driving — cold start or warm start, doesn't matter
• Clears easily, does NOT return during the same drive cycle after clearing
• Returns on the next start after key-off
• Car runs great otherwise — no drivability issues, no misfires, no power loss
• After extended sit (~1 week), first drive after did not trigger the code (LTFT decay effect)

Data from JB4 logs

• Bank 2 trim +5 to +8 units above Bank 1 consistently at idle/cruise (B1 avg 25, B2 avg 30-33)
• Closed-loop AFR matched at ~14.7 both banks (DME correcting successfully)
• WOT AFR B1 avg 13.09, B2 avg 12.97 — Bank 2 slightly RICHER at WOT than Bank 1
• Per-cylinder ignition timing balanced across all 6 cylinders at boost
• No safety triggers (LastSafety = 0)
• No misfires logged

Build context

• 2010 BMW 135i, N54
• Full built engine: Manley forged pistons/rods, ARP hardware, racing rod & crank bearings
• VTTO 2" inlets, VTTO F-RB+ turbos, VSRF ceramic 3" downpipes
• Aluminum intake manifold with 750cc port injection + Index 12 direct injectors
• Fuel-It Stage 4 LPFP
• Self-tuned 93 OCT pump gas (recently transitioned from E85 tune)
• BMS JB4, MHD Flasher
• ~3000 miles on this engine rebuild

I'm just looking for any thoughts/advice on what else I should look at. if vacuum leaks are not the issue, and the engine runs perfectly fine otherwise, is it just a bank 2 sensor that's out of wack? I reset all the adaptations but after a while the 29E1 error came back so it's definitely a persistent bugger. I have replaced the top O2 sensors but the bottom ones are still original (113k miles). Other than this one error, the engine runs perfectly - idles smooth, pulls hard at WOT, no hesitation or hiccups anywhere.