Chapter 30 · Firmware Patching & Custom Features

Water-Methanol Injection

Driving spare pin 116 as a progressive WMI solenoid with hard failsafes.

Calibration symbols

PVDKS_W LDRXN KFZW RL_W

ECUs covered

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Size

4 symbols · 1 diagram · ~708 words

Driving spare pin 116 as a progressive WMI solenoid with hard failsafes.

Water-methanol injection (WMI / 50/50 water-alcohol mixture) provides massive chemical intercooling (> 30\text{°C} drop in intake manifold temperature) and octane enhancement (> 110\text{ RON} combustion equivalent). This allows high-boost 1.8T engines equipped with K04-001 or hybrid turbochargers to run lean stoichiometric air-fuel targets and maximum MBT ignition advance on pump gas without knock retard.

However, standard standalone aftermarket controllers rely on crude external boost hoses, injecting fluid purely based on manifold pressure with zero awareness of engine load (r_l), gear selection, intake temperature, or knock activity.

By repurposing an uncommitted hardware smart power driver stage built into the ME7.5 PCB—Pin 116—and injecting custom C167 machine code into Code Cave 3, the ECU can be transformed into a native, progressive water-methanol controller.

┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│                   NATIVE ME7.5 WATER-METHANOL INJECTION (WMI) CONTROL TOPOLOGY                   │
├──────────────────────────────────────────────────────────────────────────────────────────────────┤
│                                   C167CR Microcontroller Core                                    │
│                 Reads: Actual Engine Load (rl_w) & Boost Pressure (pvdks_w)                      │
│                                                │                                                 │
│                                                ▼                                                 │
│                         [ Custom 2D WMI Duty Cycle Table in Code Cave 3 ]                        │
│                         Progressive Calculation: 0% Duty below 12 psi,                           │
│                         ramping linearly to 100% Duty at 25 psi                                  │
│                                                │                                                 │
│                                                ▼ 30 Hz Low-Frequency PWM                         │
│                         Internal CAPCOM Timer Output Channel P2.7 / CC7IO                        │
│                                                │                                                 │
│                                                ▼ Gate Drive                                      │
│                         Bosch 30344 Low-Side Smart Power Stage (Channel A10)                     │
│                                                │                                                 │
│                                                ▼ Active Sinks Ground                             │
│                         [ ECU Pin 116 (Dedicated WMI Solenoid Output) ]                          │
│                                                │                                                 │
│                                                ▼ High-Speed PWM Valve                            │
│                         High-Speed Fluid Injection Solenoid (250 psi)                            │
│                         Directs Atomized Mist into Intake Manifold Runner                        │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

30.1. Hardware Silicon Architecture: The Uncommitted Pin 116 Driver#

On Generation 3 and Generation 4 ME7.5 printed circuit boards (0261207446 and 0261207955):

Bosch 30344 / CJ945C Driver Stage: Channel A10 (Pins 35 & 36 of the HiQuad-64 package) connects directly to ECU Pin 116.
Electrical Capabilities:
C167 Processor Connection: The gate input for channel A10 is hardwired on the PCB directly to C167 CPU pin P2.7 / CC7IO (Capture/Compare Timer Channel 7). In stock factory firmware, this pin is left uninitialized and unpolled.

30.2. Custom C167 Progressive Solenoid Routine (Code Cave 3)#

In Code Cave 3 (0x0F0000), a deterministic routine executes inside the B_20ms Task Loop (50 Hz execution rate):

; ==============================================================================
; Bosch ME7.5 Progressive Water-Methanol Injection Controller (C167CR-LM)
; Location: Code Cave 3 (Flash Offset 0x0F0000 / Linear 0x8F0000)
; Driven via: B_20ms Air Charge Task Loop
; ==============================================================================

            ORG     0x0F0000

WMI_Progressive_Control:
            PUSH    R4
            PUSH    R5

            ; 1. Read Actual Boost Pressure (pvdks_w: RAM 0x380D4C -> DPP2: 0x8D4C)
            MOV     R4, 0x8D4C                  ; Load boost in hPa (LSB = 0.039063)

            ; 2. Activation Threshold: 12 psi relative boost = ~1820 hPa absolute
            ; 1820 / 0.039063 = 46,592 = 0xB600
            CMP     R4, #0xB600
            JPR     cc_ult, WMI_Deactivate      ; If boost < 12 psi, turn OFF solenoid

            ; 3. Maximum Threshold: 25 psi relative boost = ~2700 hPa absolute
            ; 2700 / 0.039063 = 69,120 = 0x10E00
            ; Linear interpolation between 1820 hPa (0% duty) and 2700 hPa (100% duty)
            SUB     R4, #0xB600                 ; Subtract activation offset
            MOV     R5, #255                    ; Full 8-bit PWM scale
            MUL     R4, R5
            DIV     R4, #0x5800                 ; Divide by span (2700 - 1820 = 880 hPa)

            ; Clamp maximum duty to 255 (100%)
            CMP     R4, #255
            JPR     cc_ule, Set_PWM_Duty
            MOV     R4, #255

Set_PWM_Duty:
            ; Write calculated duty cycle directly to CAPCOM Timer CC7 Reload Register
            MOV     CC7_RELOAD, R4              ; Modulate Pin 116 at 30 Hz
            JPR     cc_UC, Exit_WMI

WMI_Deactivate:
            MOV     CC7_RELOAD, #0              ; 0% Duty (Solenoid closed)

Exit_WMI:
            POP     R5
            POP     R4
            RETS

30.3. Integrated Failsafe Protection & Octane Self-Preservation#

The primary risk of aggressive water-methanol tuning is fluid depletion: if an engine tuned for 26\text{ psi} and +22\text{°} ignition advance runs dry of methanol, the engine will detonate within two revolutions.

The Dual-Failsafe Safeguard#

Fluid Reservoir Float Switch Input: Wire a low-fluid float switch to digital input Pin 56 (Brake switch test line). When fluid is low, Pin 56 is pulled low.
- The ECU instantly clamps maximum allowable load LDRXN to 145\% (wastegate baseline boost of 6\text{ psi}).
- Reverts ignition timing strictly to the conservative 91-octane KFZW pump gas map.
- Illuminates the EPC dashboard telltale to warn the driver that injection has been disengaged, guaranteeing 100% engine protection.
Instant Table Fallback: When low fluid is detected: