My advice as an EE designer...

Be warned: You are entering a rat hole. It's really hard to build stuff this and get it right - especially long term in automotive, even for the pros. We use extensive circuit simulation and testing on stuff like this - and it NEVER works the first time.

Don't think about selling them until you have one that works for a long time. Even then, the liability/tech support/field incidents will take all your time.

That being said, success or failure youll learn so much working on the project itll be worth it, especially if you want to go into EE. Youll make about $1 an hour if you tally up how much time it will take to make a working unit youd trust in your car :-)

You are going to need access to an oscilloscope, and someone to consult on the PCB layout.

Go for it...show this project at an EE job interview and you're hired.

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car