Click on our menu buttons immediately below to find MegaSquirt® information quickly:


Sharing Sensors with OEM Controllers

Q. I am planning an MegaSquirt® install soon. Can I keep my existing intake air temperature and engine coolant temperature sensors functioning with my stock ECU for timing, while also splicing MegaSquirt® into them at the same time for fuel? What about other sensors?

A. Yes, it can sometimes be done, and this is how:

Sensors that have a voltage output (EGO O2 sensors, throttle position sensors (TPS), manifold absolute pressure (MAP) sensors, VR and Hall ignition/crank/cam sensors, and many mass air flow (MAF) sensors) have a variable voltage signal that can be tapped into and used directly by your MegaSquirt® controllers high-impedance inputs (high impedance means they won't draw much current) without affecting the OEM ECU.

Sensors that have a varying resistance response require bias voltages through a bias resistor, and there must only be one bias resistor per sensor at any given time. Temperature sensors are typically negative temperature coefficient (NTC) thermistors (i.e. variable resistance that decreases with increasing temperature). So if you wish to share temperature sensors between your OEM ECU and your MegaSquirt® controller, you need to eliminate the MegaSquirt® controller bias resistor, and determine the value of the OEM ECU's bias resistor. You can do this as follows:

MegaSquirt® and MicroSquirt® controllers are experimental devices intended for educational purposes.
MegaSquirt® and MicroSquirt® controllers are not for sale or use on pollution controlled vehicles. Check the laws that apply in your locality to determine if using a MegaSquirt® or MicroSquirt® controller is legal for your application.
©2004, 2013 Bruce Bowling and Al Grippo. All rights reserved. MegaSquirt® and MicroSquirt® are registered trademarks. This document is solely for the support of MegaSquirt® boards from Bowling and Grippo.