Engine control unit version is Bosch Motronic ML1.3:
- Rest of the world: 0261200013 — ROW
- Switzerland and Sweden: 0261200024 — S/CH
- Boost and knock control: 0261201003 — ROW and S/CH
- Air flow meter 0280203022 — ROW and S/CH
- ECU eprom memory: 4x16kbit, 2x32kbit or 1x64kbit
Engine is managed with early Motronic with complimentary unit for turbo application. Management was advanced for its time. Three-way solenoid valve is used with spring-loaded mechanical wastegate, this makes influencing boost pressure possible. Knock control can adjust ignition timing and decrease boost when pinging is recorded by two block sensors. Upon overboost situation fuel injection is shutdown almost immediately and for a set time engine performance is regulated and decreased. All this high-technology for engine protection over 30 years ago.
Replacing eproms is straight forward, disconnect unit, remove lid and open four screws. Circuit board is folded open and eproms are visible. Early four eprom versions require soldering, later ones are socketed. Remove socketed eproms carefully not to damage chip or circuit board. Control unit is at front passengers feet, behind speaker grill. There are two connectors, one for Motronic and second for transmission. Boost and knock control unit is inside glovebox. Unit has pressure line with blowback valve attached to it, other end is fixed to intake manifold.
Like other Motronics, 745i turbo binaries can be modified for fuel maps, ignition maps, turbo specific boost cut function and more. Programmer is needed for reading and writing eproms, chip type used is either 2716, 2732 or 2764. Easy approach is a modified chip with only boost cut deleted. Hitting boost cut limit, in detail below, is happening at 0.7 bar with stock exhaust. Deleting boost cut function removes engine protection in case of wastegate or magnetic valve malfunction and may lead to engine failure in worst case scenario.
Exhaust system modifications can trigger overboost protection, common for many turbocharged cars. Decreased back pressure after turbine causes situation where wastegate is not able to follow. Boost pressure is elevated and engine protection triggered, injection stops and car shudders. According to BMW in 745i turbo this limit is reached when air flow meter registers 15% higher air flow than full throttle for more than 1.5s. This may be solved with modified chip, but once again part of engine protection is lost.
Deleting boost cut in binary file simply means changing group of values. It places protection feature out of function and no more fuel cut on boost is seen. This can be achieved by programming binary from Motronic box, downloading modified file or buying a ready chip. Remember to verify version before proceeding with downloaded file. How to work with binaries is instructed on another page, see above. Take care of maintenance items before proceeding and always monitor boost pressure (air/fuel-ratio recommended too) as safety measure.
In Sweden and Switzerland blue label ECU was used instead of white label one. Also Japan had region specific unit, a red label ECU. Sweden was first european countries pushing emissions in footsteps of US in late 70s and early 80s. ECU software was modified for this purpose, e.g. ignition map differs in slow to medium rpm range. Some say this was due catalysator but realoem is against this. Most likely these engines were tuned for low emissions (hydrocarbon, noise), as 1984 Porsche 911 Carrera. For Japanese region catalytic converter is in realoem.
BMW 3.4L engine service book gives more insight to this. Book lists temperature switch 45C/55C in troubleshooting section (only for S/CH models with EGR). Exhaust gas recirculation is nitrogen oxide (NOx) reduction technology. According to Wikipedia: “EGR works by recirculating a portion of an engine’s exhaust gas back to the engine cylinders”. Temperature switch is there for blocking EGR valve until the engine reaches normal operation temperature. EGR slows combustion, this can be compensated by advancing ignition timing (modified ECU software).