I installed a MS in my '86 RX-7 a little over a year ago and raced with it last year. I didn't know much about ECUs nor fuel injection before I started and learned a bunch in the process, both about MS and about my car. If you're a tinkerer with time on your hands I highly recommend it. Some of my comments below assume we're talking about a street car, not an IT car.
MS is a very customizable system, both from a hardware and a software standpoint. It needs to be built with the correct options to work with your car.
- If your coolant and intake air temperature sensors don't match the "standard" MS sensors, you may need to change some resistor values on the MS and use EasyTherm to calibrate the firmware. Or you could install the "standard" sensors and not have to fiddle with it.
- If your injectors are low impedence, you may need to have the optional PWM drivers on your MS.
- Different kinds of crank/cam sensors require different interface hardware. I had to build a second variable reluctance circuit on my MS to interface with the stock RX-7 crank angle sensor.
- If you're doing spark, different kinds of ignition require different output circuitry or mods.
If you're doing spark, you need to be using the Megasquirt-n-spark-extra firmware. Make sure you have the latest version (029w), as there were some bugs in prior versions. Another option is the HR (high resolution) version of the extra firmware.
If you are a tinkerer, you NEED a wideband O2 sensor. You can get a good start at a tune on the dyno, but you'll really want to tweak it afterwards to make it optimal, and you've got to be able to see where your mixture is under all kinds of situations. The least expensive one I know about is about $200 from Innovate.
You've got to have a laptop computer to be successful at this. You'll certainly be using MegaTune. Make sure you also get and use MegaLogViewer (free software) - it's wonderful. You can log long runs and see in detail exactly what happened. It also is very good at processing the actual fuel mixture from the logs and calculating new fuel maps to produce the mixtures you'd like.
If you're a die-hard, get a Palm Pilot so you can log and/or tune without the laptop in the car.
Marty Doane
ITS RX-7 #13 (sold)
2016 Winnebago Journey (home)
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