Re: Actuation signal for the fuel injectors 
 
ref:  http://www.van-cafe.com/home/van/page_870
 
ref: http://www.van-cafe.com/shop/images/ecumanual.pdf
 ...."So, the Bosch ECU computer does a lot of work, but it is not rocket science by any stretch of the imagination. The Bosch ECU is a relatively simple microprocessor signal converter and interface, which does the work of previously separate external sub-systems (e.g. the old mechanical choke has been replaced by the fuel injector pulse width (wider pulse = more gas). Variable timing provided by vacuum pressure is replaced by a lookup table of values based on engine parameters provided by sensors. Once you understand what the ECU does, it is much easier to understand problems associated with it. "......
 
....."Electronic Control Unit (or ECU)

The Digifant electronic control unit incorporates all the functions of the fuel system and ignition system and provides both the actuation signal for the fuel injectors and optimum ignition timing point for all engine operating conditions. Injection duration opening signals are provided based on the following inputs:

• Engine speed
• Intake air volume
• Coolant temperature
• Oxygen content in the exhaust gas
• Battery voltage
• Intake air temperature

The injector opening time is taken from a program in the control unit at 16 points for RPM, and 16 points for load, for a total of 256 operational points. Injection times can be determined between these fixed points for a total of 65,000 theoretical different opening points...."
 
..."Fuel Injectors

Digifant fuel injectors are electronically controlled on/off valves. A solenoid actuates a needle valve allowing fuel to be forced through the injector nozzle. All four injectors open at the same time and inject fuel directly into the intake manifold near the intake valves. Injector quantity is controlled by the amount of time the solenoids are energized. This in turn is controlled by the fuel injector pulse width, determined by the ECU.

Note: Digifant injectors (yellow body) are NOT interchangeable with AFC (blue body) injectors.".....
 
It is well worth a read through the manual to get a better understanding how the system works
 
Stuart
86 Vanagon GL 2.1L