The Raspberry is impressive, essentially desktop linux in your palm. But I am not sure that it is well suited to the precise EFI and ignition timing output needs. There are chips that specifically have precision timing control peripherals built into them. I would consider this essential. And I just looked over the Megasquirt line.. it is impressive, the latest designs even do VVT. But yikes, they are on the pricey side, like $1250. So you can have: 1 Everything that you need from Megasquirt out of the box ready to wire. $$$, plus 10 hours to wire your car. 2 Speeduino can do the essentials for most folks but takes some assembly. $$, plus 30 hours of time invested. 3 Burn some proms on a factory ECU with the help of free software. $, plus 30 hours of time invested. 3 We put our heads together and create something Fiero specific with swaps in mind. $$$, plus 100+ hours of time invested. The question is really, do you want to work on your car, or create the electronics that make your car work? I think that if I really wanted to create and program an ECU, that I would best find a forum on line that has a gaggle of folks that want to do just that. I am going to drop back and just have fun working on my 2M4. Maybe someday I will get that LZ9 3.9L, add a megasquirt, stick it to my Getrag, and learn to weld.
Of course this leads me to further thinking... A Raspberry Pi 3b is only $35 and gets you a lot more bang for buck. Quad-core ARM 1.2 Ghz with 1GB of ram and 4 usb ports, blue-tooth, Wi-Fi and HDMI output...
And that would be great the problem is development, hardware these days is cheap. Speeduino exists because one person developed it from scratch to a point where it worked then people were willing to add to it.
Personally, my opinion is that the engine's operation should be dictated by its RPM and load. VSS is superfluous; I don't want my engine behaving differently because the car is moving at a different speed...
I may be remembering wrong but the Fiero ECU gets it's vss signal from the gauges after the ppm is cut in half. What it actually uses that signal for, I'm not actually sure, it may be part of the emissions system, helping determine things like when open the egr?
Regardless it's not necessary and I'm unaware of the benefits if not for emissions and economy.
1. Eliminates stalling when you clutch in at speed. The idle settings (IAC/throttle blade, ignition timing, and air flow tables), while moving allow a higher RPM to avoid stalling during extreme transients (like clutch in and dropping the throttle), once the car us below the specified idle speed (usually less than 5 mph), it drops the idle down to the actual idle speed. So the VSS enables dual idle speed - one is used while rolling, the other is used while stopped. W/o this feature, you either have to live with stalling at speed or a higher than normal idle speed when stopped.
2. Allows the fan to turn off above 35 mph. At speed, the lower air dam creates sufficient airflow through the radiator, so the fan isn't needed. My turning it off at speed you improve life of the fan motor as well as reduce electrical load which helps fuel economy.
I once drove without the VSS (fuse was out) in my '85 2.5 automatic. It threw a CEL obviously but it also ran like crap when idling and was almost stalling when coasting or braking to a stop.
So yeah, I'd say it's quite important. That 30ish per mile thing also acts as one of the logic points to turn on the TCC.
[This message has been edited by cebix (edited 10-01-2017).]
That sounds like something that can be added to Speeduino, as it sounds like it is necessary. The fun part of roll your own is uncovering and replicating every functionality of the original ECM.. even the bits you never knew existed. Then you know every nut, bolt, and line of software.
With a MT, when coasting downhill in gear, the ECM knows not to try to adjust the idle speed beyond the preprogrammed steps. When stopped the ECM adjusts idle speed based on RPM. Without a VSS input when coasting down hill, the ECM would close down the IAC, trying to adjust idle speed, but since the engine is being driven by the wheels, it can't control it. At the bottom of a long hill, if you push in the clutch, the engine would be idling way below the target idle, or would just stall.
Sounds like they have a ways to go in their attempt to reinvent the wheel.
I remember 70s cars with carburetors that sucked. Cold fast idle sucked on them. Putting them in reverse and having them die sucked. Having to hold the brake while you lightly held the gas sucked. You had to set the "automatic" choke and fast idle by pressing the gas before starting them.
Then in the 80s we got fuel injection and many of those problems went away.
