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VEMS is a low volume commercial engine management system. VEMS is unlike most other EMS's in that it used to be public domain and then a form of open source.



The original version of VEMS was called MegaSquirtAVR and was a re-write of the popular but inadequate (at the time) MegaSquirt system. At some point it was suspected that some of the VEMS design had been stolen by a popular automotive electronics company and the design was closed from that point on.


VEMS can be purchased as a pre-made board or a complete system with several options in between. Most of the design is built with SMD components to keep size down and reliability up.


VEMS uses the AVR Atmega128 which is significantly more powerful than the original MS1 CPU.


The early MS based version was called 2.0 however that has been out of circulation for some time. The 3.0 board was the first "GenBoard" variant. Development was closed at 3.2 and the current version is 3.4. All 3.X versions incorporate one or more wide band controller.


VEMS firmware is primarily written in the C programming language, however some parts are distributed in binary and not C for IP protection reasons with an NDA.


The VEMS project is poorly documented compared with the MegaSquirt system which many believe is over documented. This has caused adoption of the system to be limited and slow.

Tuning Software

Tuning is done with MegaTune as written by Eric Fahlgren for the MegaSquirt system. MegaTune is licensed under GPL and can therefore be used by anyone.


The original MSAVR system is public domain and still available for download. This original source is obviously MegaSquirt based and therefore surrounded by some controversy. Later source was under an open source license, however since 3.2 the system is effectively closed source.


"DIY" fuel injection systems

MegaSquirt MegaSquirt II MicroSquirt MS2 Sequencer MegaSquirt 3 VEMS FreeEMS
Released 2001 2005 2007 Not yet available Not yet available 2003 2008
Processor 8-Bit MC68HC908 16-Bit MC9S12C64 16-Bit MC9S12C64 Dual 16-bit MC9S12C64 16-Bit MC9XEP100 AVR Atmega128 16-Bit MC9XDP512
Speed 8 MHz 24 MHz 24 MHz 2 x 24 MHz 50 MHz 16 MHz 40 MHz
Flash 32 kB 128 kB 128 kB 2 x 128 kB 1024 kB 128 kB 512 kB
User RAM 512 B 4 kB 4 kB 2 x 4 kB 64 kB 4 kB 32 kB
Total IO pins 34 max with mods 31 max with mods 31 max with mods 62 max 91, 119, or 152 53 max 91 or 119
ADC/ATD pins 8 (8 bit) 8 (10 bit) 8 (10 bit) 16 (10 bit) 16, 24 or 32 (12 bit) ? 16 or 24 (10 bit)
IC/OC pins 2 6 exposed 6 exposed 12 exposed 8 - 16 ? 8
Features/ Benefits Fuel and COP ignition with msextra, inexpensive, rich feature set. Fuel and COP ignition with ms2extra, good fuel and ignition accuracy. Same Features as MS-II, plus small size, sealed case, assembled. Sequential Injection (8-channels), COP (8-channels), individual trims, uses MS-II and MS-II Extra Firmware, assembled Sequential Injection (8-channels), COP (8-channels), individual trims, uses merged MS-II and MS-II Extra Firmware, assembled Sequential Injection (8-channels), COP (8-channels + 4 logic-level IGN outputs), rich feature set, assembled, exists now. Sequential Injection (6-channels), COP (12-channels), individual trims, cheap, uses free open source software and hardware designs, modular clean source code.

Note: Both MS1 and MS2 are effectively just processors, both of them require a main board to function. The three different available main boards, 2.2, 3.0 and 3.57, are cheap, reasonable, and expensive respectively. Consequently, MS1 or MS2 being cheap relies on the use of a 2.2 or 3.0 board both of which have some issues.

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