Motronic Rev Limiters - Three Types [that I know of]

Type 1 - Rev Limiter - [8 bit - multiply by 40]

First generation Motronic ECUs (8051 Microcontroller based) Rev Limits ML1.1/ML1.2 & ML3.1 - For early Motronic systems using a starter ring gear sensor.

Simply convert the number from hexadecimal (hex) to decimal and multiply by 40.

Example: From a Porsche 911 with a BOSCH type ML3.1 ECU - 0261200078_1267355211

Example: For a Rev Limit of A3h [A3h converts to 163 decimal]
Rev Limit Formula = A3h x 40 = 163 x 40 = 6,520 rpm

Type 3 - Rev Limiter - [16 bit - reverse order & divide by 4]

This first appeared in the BOSCH M3.1 and M3.3 ECUs used by BMW. That I am aware of. It may have been used first elsewhere.

Definition:little-endian
Data is stored with the least-significant byte first, then, the most-significant byte [16-bit words]...

16 Bit rev limiter - Two 8-bit hex numbers. Data is stored little-endian.

Example: From a BMW 325i with a BOSCH M3.1 ECU - 0261200402_1267357098

90 65h [little-endian] converts to 6590h [hex] converts to 26,000 [decimal]

Rev Limiter Formula = 6590h/4 = 26,000/4 = 6,500 rpm

There is no cosmic significance in the names "Type 1", "Type 2" and "Type 3". I had to call them something...

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