M7 SmazTunerECU reference
Chapter 31 of 60·Part VI of XIV

MAFless / Speed Density

Converting to speed density: FRLFN rescaling, trim unlocking, fault suppression.

ECUs06A906032LP
19 symbols in this chapter
CDLMMDFPMDKV_WFRA_WFRLFNFR_WFTBRG31G42KFZWKRKTELAMFALAMSONI_WMSHFM_WNMOT_WPVDKS_WRL_WTANSTI_B1

Open the symbol index

In this page
On this page
  1. 31.1. The Mathematical Mechanics of the Saugrohrmodell
  2. 31.2. Calibration Protocol for Permanent Speed Density Conversion
  3. 1. Rescale the FRLFN Volumetric Efficiency Surface
  4. 2. Unlock Closed-Loop Adaptive Trimming in MAFless Mode
  5. 3. Suppress MAF Sensor Diagnostic Faults
  6. Related chapters
Back to top

In high-output motorsport builds (> 350 WHP on K04-hybrid, Garrett GT28/G25, or Precision turbochargers), the factory Mass Air Flow (MAF) sensor becomes a major mechanical and electronic liability:

  1. Intake Flow Restriction: The 63 mm (or 73 mm BAM) MAF housing chokes the compressor inlet.
  2. Voltage Saturation: Peak mass airflow exceeds the maximum ADC measuring ceiling (5.00V / 655 kg/h / ∼ 285 g/s), causing the ECU to under-report cylinder filling at high boost.
  3. Sensor Element Contamination: Blow-by oil mist, water-methanol spray, and turbulent pre-compressor reversion coat the delicate heated platinum film, skewing fueling calibration.

While amateur tuners simply unplug the MAF and accept factory limp-mode defaults, Bosch ME7.5 contains an advanced physical Intake Manifold Pressure Filling Model (Saugrohrmodell). By calibrating this subsystem, the ECU can be converted to operate in a pure, factory-clean Speed Density / Alpha-N mode with full closed-loop wideband lambda trimming.

code
┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│                   BOSCH ME7.5 SAUGROHRMODELL (SPEED DENSITY) CHARGE CALCULATION                  │
├──────────────────────────────────────────────────────────────────────────────────────────────────┤
│           [ Engine Speed (nmot_w) ]         [ Throttle Plate Angle (dkv_w) ]                     │
│                        │                                   │                                     │
│                        ▼                                   ▼                                     │
│           ┌─────────────────────────────────────────────────────────────┐                        │
│           │            FRLFN Characteristic Filling Surface             │                        │
│           │      Base Volumetric Efficiency: VE = f(nmot, dkv)          │                        │
│           └──────────────────────────────┬──────────────────────────────┘                        │
│                                          │                                                       │
│                                          ▼ Base Relative Filling (rl_base)                       │
│           [ Manifold Absolute Pressure (pvdks_w / MAP Sensor G31) ]                              │
│           [ Intake Air Temperature (tans / IAT Sensor G42) ]                                     │
│                                          │                                                       │
│                                          ▼ Corrected via FTBR (Gas Law: P = rho * R * T)         │
│           ┌─────────────────────────────────────────────────────────────┐                        │
│           │      Synthesized Relative Cylinder Air Charge (rl_w)        │                        │
│           └──────────────────────────────┬──────────────────────────────┘                        │
│                                          │                                                       │
│       ┌──────────────────────────────────┴──────────────────────────────────┐                    │
│       ▼                                                                     ▼                    │
│ [ Fuel Injection Duration ]                                      [ Ignition Advance Map ]        │
│ ti_b1 = rl_w * KRKTE * LAMFA                                     KFZW = f(nmot_w, rl_w)          │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

31.1. The Mathematical Mechanics of the Saugrohrmodell

When the MAF sensor signal (mshfm_w) is absent, the ECU calculates relative cylinder filling (rl) from the ideal gas law:

rl = FRLFN(Nmot, αdk) × (PdsPambient ) × FTBR(Tans)

Where:

  • FRLFN (Kennfeld Normierte Füllung): The primary 3D volumetric efficiency matrix (Address 0x01A240 in 06A906032LP, 16 × 16 grid). It maps engine speed and throttle angle to base cylinder filling under standard temperature and pressure.
  • Pds (Saugrohrdruck): Manifold absolute pressure measured by the charge pipe MAP sensor (G31 / Pin 101).
  • FTBR (Temperaturkorrekturfaktor): Density correction factor inversely proportional to absolute intake air temperature in Kelvin: FTBR =293.15 K273.15 + Tans (°C)

31.2. Calibration Protocol for Permanent Speed Density Conversion

To eliminate the MAF sensor cleanly without triggering limp mode or losing closed-loop fueling adaptions:

1. Rescale the FRLFN Volumetric Efficiency Surface

  • In 06A906032LP, open FRLFN at 0x01A240.
  • In big turbo applications with high-lift camshafts or ported cylinder heads, low-RPM volumetric efficiency drops slightly while high-RPM volumetric efficiency increases by 15% to 25%.
  • Log wideband lambda (lamsoni_w) and short-term fuel trim (fr_w). Smoothly adjust cells in FRLFN until fr_w fluctuates within ± 2.5% across all throttle positions.

2. Unlock Closed-Loop Adaptive Trimming in MAFless Mode

In factory software, when the MAF fails, the ECU disables long-term fuel trim learning (fra_w).

  • Codeword CW_LRA (Lambda Regulation Adaptation Mode):
    • Set bit CW_LRA.0 = 1 (Enables additive and multiplicative lambda trim adaptation during Alpha-N backup mode).
    • This ensures the wideband LSU 4.2 sensor continues continuously adapting to ambient weather and fuel density variations.

3. Suppress MAF Sensor Diagnostic Faults

  • Codeword CDLMM (Codeword for Air Mass Meter Diagnosis):
    • Using me7_dtc_manager.py (DOC 34), set fault classes for P0102 (MAF Low Input) and P0103 (MAF High Input) in array CLA* to 0x00.
    • The Check Engine Light remains completely dark, and readiness monitors pass unconditionally.
  • DFPM Error Classes:

Cross-referenced on shared calibration symbols, not on subject matter.

→Chapter 12 — RAM Logging & .ecu Files — MSHFM_W , DKV_W , TI_B1 , TANS , FR_W , FRA_W

MSHFM_W · DKV_W · TI_B1 · TANS · FR_W · FRA_W

→Chapter 25 — Troubleshooting & Failsafes — DKV_W , TANS , G42 , FRA_W , LAMFA , NMOT_W

DKV_W · TANS · G42 · FRA_W · LAMFA · NMOT_W

→Chapter 60 — Post-Dyno Verification — FRA_W , LAMSONI_W , RL_W , KRKTE , NMOT_W , KFZW

FRA_W · LAMSONI_W · RL_W · KRKTE · NMOT_W · KFZW

→Chapter 3 — Benchmark Calibrations — G42 , G31 , DFPM , LAMFA , KFZW

G42 · G31 · DFPM · LAMFA · KFZW

→Chapter 35 — High-Speed Logging — PVDKS_W , LAMSONI_W , RL_W , NMOT_W

PVDKS_W · LAMSONI_W · RL_W · NMOT_W

→Chapter 55 — Flash Map & Task Tree — TI_B1 , RL_W , DFPM , NMOT_W

TI_B1 · RL_W · DFPM · NMOT_W

Esc
↑↓ move↵ openEsc close