Computer Operation

The computer controls 4 circuits: EFI fuel control, the air/fuel mixture fine-tuning (using oxygen sensor), electronic spark advance, and idle speed control.

In open-loop operation, the air flowmeter and the fuel flowmeter are used to determine mixture strength. This occurs when the engine is cold or when acceleration is needed. When the oxygen sensor is hot and cruising operation occurs, the system enters closed-loop operation.

In closed-loop, the oxygen sensor reports the amount of unburned oxygen in the exhaust to the computer. The computer then drives the control pump faster or slower to adjust mixture.

Three other sub-systems are involved in computer operation. The idle speed is controlled by a motor on the throttle body, which adjusts the throttle stop to maintain idle in cold operation or with A/C on. A Power Module inside the air cleaner near the injectors provides 23-volt current for operating the EFI system. Finally, an Automatic Shut-Down Module terminates power to the fuel pumps whenever the ignition key is on, but no signal is received from the distributor. During cranking, the ASD allows the pumps to operate, but if the fuel pressure switch does not close in 10-20 seconds, the pumps stop. This prevents flooding if the injectors are leaking.