I'm trying to find info on how to use the megasquirt as a piggyback ecu. I had someone tell me on here before it was possible, but i never can find info on how to use it as a piggyback. Maybe I don't quit understand because I'm just starting out learning about how ecu's work. I'm not sure what version to look at or what I need. I tried the search on here but there are way to many posts to go through them all. Is it possible to use it like this and if so where should I go to find the best info on the tried and true methods that work on our cars for this( oh yeah i have a 97 rs). I've downloaded all the megasquirt manual but not sure if I need all the options for what I'm trying to do. Any help would definately be appreciated.

If you wanna control fuel (easily)

Grab your tach output from your ecu (or grab the crank sensor). Mod up the MS circuit board accordingly for the crank sensor.

Cut your injector harness, grab some bosch connectors from Napa and make your own connections to your injectors.

Wire them into the MS.

Drill/tap a new Intake temp sensor into your manifold ($15 part at Napa, Advance Auto) check msefi.com for details.

Add an additional Coolant sensor by teeing off you existing coolant sensor by using a NPT tee from a hardware store. (Coolant sensor also available at Napa, Advance Auto)

Wire up 12v, switched 12v. Go!

To be more specific, you will need to feed the MS a o2 sensor and TPS signal from the ECU.

This may not seem like its piggybacked to you but it is. If your looking to use the MS as a extra injector controller and leave the Factory ECU control the primary injectors then you can do that also.

You will still need to connect up the MS the same way but the injector harness will need to connect to the secondary injectors. The VE table you set up will need to be complete as if MS was controlling the primaries too. In the N/A bins of the VE table you will need to input the value "1". MS does not understand 0.

Terry

ok, but are you able to use it just for the 4 primary injectors without having secondary injectors? Also, I've read that it is good to find someone that has the same setup I'm beginning with, so that I can start off tuning somewhere in the general area of how my car will run. Are there any suggestions anyone has on what is the best version used on 2gnt (Msns, ms v. 2.2, ms vs.3)? I really appreciate the help you are giving me so I can start out on this project on the right foot. Thanks....

Yes, the traditional design is using the MS for 4 primary injectors. Many people are using the v2.2. The v3.0 has tach noise issues and although some people have had luck using an alternate circuit, there is no guarenteed fix. The VR circuit has worked for a few people but not everyone. I am currently working on this but not sure if this is going to pan out or not.

Terry

sorry to revive an older topic, but if you are using megasquirt solely to control fuel do you need to wire the fuel pump to the megasquirt, or will the stock ecu run it?

98 GS
Super 17c Turbo, Portfueler, Je pistons, Eagle rods, Etc.

The Stock ECU will run the fuel pump just fine.