So next i'm going to start talking a little bit about the fuel injection system we are going to be tuning. We will be working with Motronic 4.4, Volvo’s and Bosch’s latest ECU* for most 850’s and 98 C/S/V70’s. This ECU is used on both non-turbo and turbo Volvo’s. It appeared as early as 1996 models as my 1996 NA has M4.4*.
Motronic’s main brain is a Siemens SAB83C517A-5N18 CPU*. This an 8 bit 8051 based CPU* that can operate up to 18mhz. It is clocked at 16Mhz on M4.4*. It features 32K x 8 ROM, 256 x 8 on-chip RAM, 2K x 8 on-chip RAM (XRAM), Four 16 bit timers/counters, 10 bit A/D converter with, 12 multiplexed inputs, Two full duplex serial interfaces, Nine ports: 56 I/O lines, 12 input lines,Mask programmable ROM (Internal ROM protection). M4.4 also contains an Intel AN28F010 EEPROM. It is 128kb in size. You are probably wondering how can a 8 bit cpu that usually can only address 64kb address 128kb of memory? Well Bosch implemented a technique called bank switching. P5.7 on the cpu triggers the 17th address line needed to access the upper 64kb of the 128kb. So Motronic 4.4 has two main flash banks, the upper and the lower. The ECU* uses all of the sensors mentioned above except the pressure sensor.
Being an 8 bit system and 10+ years old, the software isn't too hard to understand. Motronic 4.4 uses a MAF* to measure the actual mass of the air coming in. It then uses this information along with RPM* and injector constant and the TPS* to calculate load. This load value is used all throughout the software and will be gone into more detail in the next section. The software also contains Maps* such as main fueling maps, ignition maps and requested load (boost map) to name a few. I won't go too into detail about the software here as all of the other sections will contain information on tuning the software, so I don't want to spoil everything here.