Remapping Motronic

For those cars whose engine management system is Motronic 1.3, it is possible to wipe the chip in the ECU and recode it for custom performance. This is known as Remapping.

Components

Inside your ECU is a chip, known as an EPROM (Erasable Programmable Read Only Memory). With the aid of an ultra-violet eraser and a programmer, it is possible to blank your chip and write your own map to govern fuelling and ignition timing.

The EPROM in a 320i or 325i is a 27C256 type, a 28-pin DIL (Dual In-line) chip. It contains 256K-bits of CMOS memory (arranged as 32,000 words x 8-bits). The Motronic digital fuel injection system uses an 8-bit processor. The word length is 8-bits. Each 8-bit word contains an executable instruction or a piece of data. The data is arranged in Hexadecimal (Hex) format for use with computers.

Programming Langauge

The chip program is written in Assembly langauge, which can be translated into Hex or even binary code by software such as that included with an EPROM programmer. An example of this is as below from a standard BMW 325i chip (part section of the code):

Assembly Language:

MOV F0h,0Ah JNB F0h,51h DJNZ 08h,4Eh MOV A,09h CJNE A,#00h,24h ORL C1h,#C0h CLR AFh CLR 93h MOV C6h,A SETB AFh ANL C1h,#3Fh MOV A,#F4h ADD A,C6h MOV C6h,A MOV A,#01h ADDC A,C7h MOV C7h,A ORL C1h,#80h SETB 93h

Hexadecimal Language:

0---1---2---3---4---5---6---7---8---9---A---B---C---D---E---F

85 0A F0 30 F0 51 D5 08 4E E5 09 B4 00 24 43 C1

C0 C2 AF C2 93 F5 C6 D2 AF 53 C1 3F 74 F4 25 C6

F5 C6 74 01 35 C7 F5 C7 43 C1 80 D2 93 75 08 0A

80 67 B4 01 24 43 C1 30 C2 AF C2 92 F5 C4 D2 AF

Specific lines of the program set the various parameters controlling the fuelling map, fuel octane rating, ignition timing, rev limit, etc.