Megasquirt - Stim Testing


Intro - Stim types - Testing


The Megastim/ JimStim is a piece of test equipment complementary to the Megasquirt. It is an excellent tool to use during and after assembly of the Megasquirt to confirm correct operation and to learn about how the Megasquirt reacts to the various sensor inputs before installing onto an engine.

Stim types

The Megastim is a the entry-level stim

It simulates:
- CLT sensor
- MAT sensor
- O2 sensor
- Distributor or EDIS RPM signal (only)
It has LEDs to indicate:
- the two output channels of the batch-fire Megasquirt
- fuel pump
- idle output

The JimStim is a more fully featured stim

It simulates:
- CLT sensor
- MAT sensor
- O2 sensor (narrowband or wideband)
- spare potentiometer for additional sensor
- Many RPM signals equivalent to OEM trigger patterns with both crank and cam outputs. 'Hall' or 'VR' type signals.
It has LEDs to indicate:
- the two output channels of the batch-fire Megasquirt
- two bi-colour LEDs for stepper idle
- fuel pump
- idle output
- four spare LEDs for spark or fuel indication

The JimStimX is an optional board to complement the JimStim when used with the MS3X.

It plugs directly into the MS3X connector and has:
- 8 injector LEDs
- 8 spark LEDs
- 6 'PWM' LEDs
- 3 potentiometers for analogue inputs
- 4 switch inputs
- connection for the MS3X cam input


If you purchased a kit, you will need to assemble your stim, see:-

  • JimStim information
  • Megastim v1 information
  • Megastim v2.1 information


    Having assembled your stim, you need a source of around 12V DC e.g. bench power supply, 'wall wart', mains adapter or FUSED car/bike 12V battery. (A small 9V battery can be used, but may only last 15 minutes.)
    - Plug the stim into your Megasquirt
    - Connect your computer to the Megasquirt with serial or USB. See the Serial Setup page if you haven't already.
    - The stim is marked with +/- connections. Be certain to connect + from the power supply or battery to + on the stim.
    - Turn on the power source and turn on the power switch on the stim (if fitted.)
    - If this is your first time, then you may need to load firmware to your Megasquirt.
    - Ensure your tuning software is installed if you haven't already.
    - Now, open TunerStudio.
    - All being well, TunerStudio will connect and show some gauges. If it is showing "Offline" then you have a problem.
    - Vary the CLT, MAT, TPS potentiometers (pots) and confirm that the on-screen gauges are moving.
    - The response from the O2 pot will depends on the EGO/O2 settings in TunerStudio.
    - The MAP sensor isn't tested with the Stim - you need a small syringe and some hose. (Inkjet refill syringes are handy.)
    - Ideally you now want to set the stim wheel mode to match the wheel mode your engine uses. The JimStim has support for a wide range of wheels. If you have the MegaStim them you can only simulate distributor or EDIS.
    - It is common that the 'VR pots' on the Megasquirt mainboard may need a little adjustment to pick up an rpm signal when testing on the bench.
    to be continued......

    If you have a question, comment, or suggestion for this FAQ please post it on the forum.

    No part of this manual may be reproduced or changed without written permission from James Murray and Ken Culver.