Single-bank fueling: what it actually is
The community's most-misread N54 term. Single-bank fueling is an MHD flash option that runs the DME on bank-1 oxygen sensors only — built for single-turbo cars.
"Single-bank fueling" sounds like hardware — one fuel rail? one pump? one bank of injectors? It isn't. In every thread that matters, the term means one thing: an MHD flash option that runs the DME's fueling and boost control from the bank-1 oxygen sensors only, with both bank-2 sensors physically removed. It exists for single-turbo N54s, and it's the rare option that makes a car more honest, not less. Here's what it is, when it's right, and what you give up.
Why it exists
A stock N54 has two turbochargers, two exhaust streams, and four oxygen sensors — a wideband primary and a cat-monitor secondary per bank. The DME trims cylinders 1–3 against bank 1's sensors and cylinders 4–6 against bank 2's. Two closed loops, two exhaust streams: correct.
A single-turbo conversion collapses that into one manifold feeding one turbine. Keep both banks active and the DME still trims cylinders 1–3 and 4–6 separately — but they're breathing through the same collector now, so the two trims fight over one shared exhaust stream. It runs. Not well. Single-bank fueling fixes the geometry: one sensor view, one trim, one loop that matches the hardware.
What changes on the car
- **Remove and unplug both bank-2 sensors** — primary wideband and secondary. The DME is told, by the flash, not to expect them.
- **Bank-1 primary goes post-turbo, pre-cat** — the downpipe bung right after the hot side.
- **Bank-1 secondary goes post-cat.**
That placement is deliberate, and it's why the option exists at all: single-turbo downpipes put bungs close to the turbine, and wideband sensors aren't built for pre-turbo heat. Many single-turbo cars end up with one sensor pre-cat and one post-cat — the same arrangement inline-six OEMs ship from the factory.
What changes in software
It's a flash-time selection in MHD, not a hardware kit: no DME re-pinning, no harness surgery, no adapter. It rides alongside whatever map you flash, and it coexists with a JB4 if one's installed — the piggyback reads fueling state and doesn't care which bank the DME is listening to.
What you give up
The honest trade is diagnostic granularity:
- With two banks, a lazy injector on one bank shows up as that bank's trims drifting. With one bank, a single weak cylinder is diluted by five healthy ones in the shared stream — the wideband sees the average, not the outlier.
- Per-bank AFR logging is gone from your datalogs; you get one authoritative lambda.
- Cat-monitoring, already nominal on most converted cars, is reduced to the bank-1 secondary.
The community's own framing cuts both ways: when oxygen sensors are marginal (heat-cycled hard on single-turbo cars), banking on one good pair is safer than two questionable ones — you at least get an accurate AFR instead of two arguments.
Where it sits in the fueling picture
Single-bank fueling is about measurement, not delivery. If you came here researching how to feed a big single turbo, the delivery ladder is separate:
| Question | The guide |
|---|---|
| How does the DME measure AFR after a single-turbo swap? | This one — single-bank fueling |
| How do I get more fuel into a 500+ whp N54? | Port injection |
| How do I feed the low-pressure side (and a second pump)? | LPFP upgrades |
| Why does ethanol move the whole target envelope? | Why E85 changes your boost targets |
Sources
- The original single-bank fueling discussion (e90post): [MHD single bank fueling thread](https://www.e90post.com/forums/showthread.php?t=2043273)
- Community verification on JB4 coexistence (JB4tech): [single bank fueling + JB4](https://www.jb4tech.com/forum/model-specific-engine-tuning-modification-discussion/n54/833917-mhd-single-bank-fueling-jb4)
Is single-bank fueling a pump or injector upgrade?
No. Despite how it sounds, it's software plus oxygen-sensor placement: an MHD flash option that lets the DME fuel and control boost from the bank-1 oxygen sensors alone. The fuel pumps and injectors are separate decisions with their own guides.
When should a single-turbo N54 run single-bank fueling?
When the exhaust is one manifold feeding one turbo. Two oxygen sensors watching separate cylinder banks that share a collector means the DME trims two halves of one exhaust stream against each other — it runs, but not well. One manifold, one sensor view, one trim is the physically honest configuration.