Danish VW beach buggy Vems v3.1 project. 4 cyl boxer engine, port inj, wasted spark.

Im still soldering but having a hard time finding the right dokumentation for v3.1


Before pictures.



So far i have mounted.

Flyback diodes M 724 B14 ZP -> lowZ? confirmed ok.

Transient protection diode 1.5KE18A

L3 1R5 ok

Resistor briged 5X-1-103


Flyback wire



4 IRF640N inj FETs

4 22ohm resistors

2 N408AB 14N40FVL FETs

Not mounted jet.


Anything else missing ?




I have connection problems

Any tricks to connect a very old board (number 57) to vemstune ?

im receiving 192byte's from ECU (sending 84byte) before getting "Could not find ECU"


Problem with comunication fixed, forced into bootloader mode and updated firmware to "1.1.94 bootloader update"

Whats the recommended firmware version ??

Trigger Setup

Is this set up for primary hall sensor ?


Not really, you need for primtrig HALL: SJ2 closed !!!, SJ6 open (which is so), see GenBoard/Manual/InputTriggerHardWare



Trigger Setup

I found out that I have a VR sensor instead of a Hall sensor... dooh ;-)

R30 = Removede again

C88 = Not mounted

R55 = 10Kohm

SJ1 = Shorted

SJ2 = 10Kohm <- is this ok ?

SJ6 = Shorted

D14 = Not mounted

R56 = mounted again = 10Kohm

C30 = ok

R57 = 75Kohm

R87 = 1000Kohm

C38 = ok

R88 = 10Kohm

C31 = ok

C39 = ok

Mesurement between Trigger1 connecter and LM1815 pin3 = 20Kohm = ok

Mesurement between LM1815 pin12 and AVR pin 29 = 0ohm = ok


Grounding on fiberglass buggy

Where should i put my grounds ?

Engine is under the black cross

Battery is under the blue cross

Ecu is mounted on a 2mm stainless steel plate, i have prepared a line of 6mm bolts for grounding on the plate.

Where to put GND5. (powerground) ?

Where to put sensor GND. ?

Picture ->

  • 20/04/2014. Ok i found som 50mm2 cable that i will connect battery -> ecu plate -> engine.
  • I will shield cranktrigger (at common ground on ecu plate)
  • i will shield wires from ecu to ignition coil (at common ground on ecu plate)



Bosch MAP sensor gives weird voltage (prolly not connected properly)

[Bosch MAP sensor 0 281 002 316 pdf] (0.2-4bar): normal 4bar Bosch

the problem is that the MAP sensor gives about 4.2 volts when the engine is stopped (101 kPa).

Vemstune shows about 337kpa which approximately matches the 4.2V input: (4.2 - 0.2) * 400/4.6=347 kPa (would be good after offset tuning).

MAP sensor is coupled direct onto the PCB where the internal normally sit, by a cable. That's OK.

I there anyway to calibrate the map-sensor.

Calibration requires at least 2 points. If you can measure at a different pressures, than calibration might be possible.

It would be nice to measure at

Do you suspect it's reverse slope (lower voltage for higher pressure) ? I guess there is no accidental pullup to 5V (at least unlikely: for MAP, there is no pullup resistor provision onboard).

According to datasheet, the sensor is normal analog voltage, NOT frequency output like some Ford sensors.

I have checked the wiring again, and you are right..... ground and Vcc is mixedup


I have triple checked map-sensor wiring and it actually not wrong, i nearly burned it trying to swap Vcc and ground ;-)

Picture internal wiring ->


Changed the Map-sensor to MPX4250... problem solved

Engine is now running :-) but since missing serialnr: ignition is locked at 10 degrees

Vems 3.1 board no57 firmware 1.2.11

vems forum tread,2290.0.html

Fixed bootloader in serialnr 57, upgraded to uhex.

Stepper (push-pull) output diode protection

What diodes to use on stepper output ?

VEMS (v3.0 and) 3.1 had onboard provision for 2 SMB diodes per stepper output

I think I also need D45 on the 12v_p to supply 12volt ?

and from 3.3 there is no D45.

Now running without D47-D54 and D45 is replaced by a wire. Seems to work