Small 4.75 L liter gas engine, block compatible with MTZ tractor 4 cylinder, 1500 RPM powerplant (grid) application

(some comments on this page are Hungarian)

While 1st serial port is connected to VemsTune,

2nd serial port acts as a "modbus RTU slave" and accepts commands from a "modbus RTU master" device.

ECU serialnr=8538 ?


See MembersPage/PhatBob/UserGuide

Supply +12V or +13.5V (not +24V !!!)


5 EGT (order comment: "5 EGT inputs") 4 individual + 1 mixed

CLT Coolant Temperature (hengerfej víz temperature)

MAT Manifold Air Temperature (gázkeverék temperature osztócsoben) 0-5V signal

TPS (folytószelep pozíció)

MAP : Manifold Absolute Pressure, pneumatic connector (szívócsonyomás, abszolút 0-300 kPa ?)

Trigger input

Warning: since this engine has primary trigger on the camshaft, not the crankshaft as usual, 6-1 is not suitable, only 8-1 or 12-1 or 12-2 (or some even higher toothcount).

EC36/28: +5V output for HALL sensors (max 50mA recommended)

Ignition outputs (1,3,4,2 firing order)

4A biztosítékon át a gyújtótrafó másik vége tápfeszre (+12V vagy +24V DC) van kötve

Injector outputs

LPG 3.6 Ohm injectors

not directly related to cyl, going into manifold

Starter config

IAC PWM output

Possible PWM voltage for Woodward 5-32VDC

  • TPS in EC36/1 0,75-4,25VDC exact range configurable (within 0-5V)
  • 0-90% (or 10-90% )
  • EC36/pin11 (ign4) 0/5V (max: 1.1mA) seems to work
  • dropped: EC18/pin4 (Stepper A) 0/12V

Woodwars spec:

PWM Command Input (+PWM at pin 11, PWM ground at pin 3)—This actuator can be configured to handle a PWM signal from a high-side or low-side opencollector or open-drain source, as well as from a push-pull (customer pull-up) source. The necessary pull-up and pull-down voltages to accommodate the

open-collector sources are handled within the L-Series actuator. Nominally, the frequency of PWM is 1 kHz, but it will handle the full range of 300 to 1500 Hz

ETC output (v3 electronic throttle, which outputs upto 8kHz PWM with quartz precision) was NOT requested, and not connected to Econoseal pin.

Lacking ETC output, we used a small patch to use 4x IAC frequency (max 1000 Hz), and mostly used at 600 Hz (150 Hz configured in VT). Seemed to work better than 400 Hz (configured 100Hz).

The signal that works well for PWM IAC, showed up noisy in the woodward valve: woodward's input calculation is not robust at all: No outlier elimination, not even averaging. The PID in the woodward is configurable, and it was possible to slow it slightly (this is a powerplant, not a racecar) to get smooth output.

Mixture valve


2nd RS232 for CRC protected special commands, voltage measured from pin5 (GND) base

1st RS232TX (EC18/14) (female DSUB9/3)

1st RS232RX (EC18/15) (female DSUB9/2)


2nd RS232TX (EC18/6) (female DSUB9/2)

2nd RS232RX (EC18/12) (female DSUB9/3)

GND EC18/17 (DSUB9/5)


(02) 06 00 XX VV 00 (CRC CRC)

XX table:

Read (subset or all) runtime vars command

Standard modbus command 03 (Read holding registers) example:

(02) 03 00 XX 00 LL (CRC) XX = index, LL = length in words (max 38)

  • response is 2*LL bytes (as in modbus standard), from 2*XX byteoffset. The full set of runtime variables can be read in 1 or multiple queries.

Register/Address for reading

Eg XX=07 and LL=01 gives the RPM value (byteoffset=14) in big endian format 0..25500 RPM

Byte offsets (for some important values):

See <VT installdir> /config/vemsTune-v3-1.2.23.ini


- EGT1, EGT2

- worst knock value

- relative knock values 0..7

- errors, trigger error (hibák)

- individual power (gyújtás kihagyás)


- base timing ("TDC after trigger" value not changing during operation, set from VemsTune, primary trigger dialog).

- lambda SP (SP ?)

K-Thermocouple. Andor, Viktor, please verify from your paper, or device behavior that EGT uses mcp3208 channel 0 and 1 (4 and 3 are almost certain)

For some reason, CLT-out, CLT-in and MAT are on K-thermo, instead of the more common and more precise NTC.

MAT and CLT-out values: configured to 17 point curve, with -1Celsius starting point... That way (in this fw) it will measure from mcp3208 instead of AVR ADC.

Example curve for "egt cal of 75" (only the first 2 counts... Most likely the max configurable CLT and MAT is 155C, so 145..155C instead of 145..217C configured, slope effected accordingly) (calculated with 3.55V = 803 deg C)

0 -1

0,32 72

0,64 145

0,96 217

1,28 290

1,59 360

1,91 432

2,23 504

2,55 577

2,87 649

3,19 722

3,51 794

3,83 866

4,14 936

4,46 1009

4,78 1081

5,09 1151

WBO sensor connection

Digital inputs

Digital output

Knock sensor 1pcs.

Base Config made; Configured for: