Jim,
According to 505 Turbo Electrical Service Manual:
"...The basic amount of time for the injectors to operate
is determined by the signals that the INJECTION ECU receives
from the altitude sensor, the air flow sensor, the microswitch,
and the engine RPM signal from the IGNITION ECU and the Start
signal from the ignition switch. This calculated Basic Injection
Duration signal is sent to the IGNITION ECU.
The Basic Injection Duration signal is modified by the following
signals: (1) the battery voltage; (2) the exhaust oxygen content
measured by the lambda sensor; (3) the engine temperature sensor;
and (4) the Full Load Data signal from the IGNITION ECU. The INJECTION
ECU provides a ground for the injectors for a period to last
for the modified Basic Injection Duration time..."
---In other words--the IGNITION ECU does not affect injector duration, in fact, injector duration affects the ignition according to the above paragraphs. And that makes sense--injector duration decisions are made solely by the INJECTION ECU, as they are on any Lx-Jet system.
BTW, the "full load data signal" generated by the IGNITION ECU and sent to the INJECTION ECU combined with the closed throttle microswitch takes the place of the integrated throttle switch found on most other Lx-Jet applications. The word "data" is confusing because it is simply an on-off signal. The ignition ECU decides when the engine is under full-load and tells the injection ECU to go extra-rich.
Joe