Stock ECU adapter. DIY USB Tuning on the fly. (Concept)

[Skylar]

I'm getting excited for this.

Gonna be a lot of hard work but if you can get a full ECU working, it'll be awesome.

[SamsTA22]

I hate to sound discouraging, but I don't see this working.

.... At least not in any marketable form... or soon.

There are a few reasons:
You're programming a PIC. Now, I admit, I am biased against them (bad experience). But they kind of suck for complicated things like standalone ECUs. It would be possible to make a basic interceptor type computer, like an SAFC or whatever (more info later).

Do you know what kind of buffering is appropriate for your I/O lines? e.g. you weren't planning on just wiring the CAS signal (which comes the distributor) directly into the Micro?

Also, a lot of the sensor inputs (most of them, actually) are just analog voltages. So you'll need an ADC to measure them. And a DAC to output the modified signal(s). (I dont think a digital pot will work very well.)

Then, if you want to directly modify output signals, theres just further complications, like how to synchronise the micro with the engine speed. This is where you approach standalone ecu functionality. Coding becomes way more complicated.

USB is way more difficult to learn how to work than serial or parallel ports. Most people in this situation would just use something like FTDI so they dont have to worry about dealing too much with usb.

Your software would have to be able to program the device, as well. Like being able to display the graph data. The most basic intercepter will just have a table, 16x16, 16x20, 24x24, whatever you choose. (Ideally, the user would be able to control the resolution). The table would just be RPM vs Load, filled with the modified load values.
Then your code would have to be able to interpolate the map, so it isn't ridiculously crude. That depends on your programming/maths ability, I guess.

Anyway, back to the PIC thing. Did you know you can get ARM cortex M4 development boards on ebay that has a DAC and ADC, along with a USB interface, and enough I/O lines for a full features ECU? for $20?
Of course, they dont have any buffering, or multiplexing on the ADC/DAC. But it would be easy enough to add that.

Or there's the Megasquirt. You're guaranteed to learn a few things about engine management trying to get one of those things to work. Damn good design, I think they just ask a bit too much of the average user. Or even the average tuner for that matter.

Alternatively, some MAF interceptors can be found pretty cheap nowadays. It'd probably be a bit of a challenge to tune one to work with a MAP sensor, though. But not impossible.