Explain this fuel injection wiring diagram

From the pdf found here:


On the Car Diagnosis. Your Volvo's engine uses port fuel injection firing all injectors simultaneously with some cross-over occurring within the plenum. The injection pulses can vary considerably, and Volvo FI set-ups fire the injector twice per revolution (keeps the valve wet between intake cycles) to prevent hardened deposits from forming on the valves. This often results in enough fuel being present for near-normal engine operation on three injectors. All four injectors fire at the same time on +12V current supplied from the radio suppression relay (later cars) or the car's power supply. The injectors fire when the FI ECU grounds the circuit. Basic diagnostic tests for injectors include:
 
Batch fire. From the article you linked:

"D-Jetronic is a grouped injection system, where half of the injectors are in a group that are pulsed simultaneously. In four-cylinder implementations, there are two cylinders per group. There is one injection pulse per power cycle. With grouped injection, one cylinder gets the injection pulse right before the intake valve opens, the other cylinder gets the injection pulse about 180 degrees before the intake valve opens."
 
Yea, that was in the 60's. 20 years later why didn't Volvo use individually firing injectors?
Because they outsourced that engine system to Bosch. Whining about it isn’t going to change that. Contemporary car companies (Honda, Toyota, domestics) were still using carburetors. Some contemporary Bosch injection systems, like K-Jetronic, were continuous injection - a constant spray. No better, no worse, than this system.

Do you want help with your Volvo?

Or do you want to complain?
 
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