Ok, here is an updated circuit. If anyone is following and wants to try it, feel free (It might take me a while). I would say make injUS delay at least 1000, or if you are coyotex, just dial it in with that diagnostic port
This goes in line with the injector lead, and the connector already has 12v and ground, and you should already have a negative injector tap.
Here is the opto I'm using:
http://mouser.com/Search/ProductDeta...key859-LTV-815
The diode is a 1n4004
http://mouser.com/Search/ProductDeta...lkey821-1N4004
The resistors are 10k ohm and 470 ohm