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Cold Start Injection System

To improve engine starting when coolant temperatures are low, a supplementary injector is installed on many EFI engines. The cold start injection system consists of the following components:

1) Cold Start Injector

2) Start Injector Time Switch

3) ECU (most EFI/TCCS) Cold Start Injector

The cold start injector is located at some central location in the intake manifold. It is designed to supplement the cranking air/fuel ratio and prime the intake manifold in much the same way as a choke valve does while cranking a carbureted engine.

This injector, controlled by the start injector time switch and ECU, sprays a finely atomized mist of fuel while the engine is cranked to improve the speed with which the engine starts. To prevent engine flooding, the injection time is limited by calibration of the start injector time switch and a timer in the ECU.

Cold Start Injector Control

Start Injector Time Switch

The function of the start injector time switch is to control the cold start injector ground circuit and to determine maximum injection duration while cranking. Its bi-metallic switch is heated by both engine coolant and an electrical heater.

When the engine is cranked, current flows from the STA circuit of the ignition switch to the cold start injector. Current also flows to the heater coils of the start injector time switch. When the bi-metallic contact of the start injector time switch is closed, current flows through the STJ circuit to ground, causing the cold start injector to deliver fuel.

Toyota Cold Start Injector Time Switch

As the bi-metallic switch is heated by electric current, it opens, causing the STJ circuit to be broken. This prevents the cold start injector from delivering fuel.

Heater coils 1 and 2 are wired to accommodate heater current flow whether or not the time switch is closed.

When the time switch contact is open, current can still flow through Heat Coil 2, thereby preventing the contact from closing in the middle of a cranking cycle.

The start injector time switch comes in several calibration values. These values determine the maximum temperature and maximum time that the switch will remain closed while the engine is being cranked. Specifications for switch calibration are stamped on the switch. Application information is available through parts and technical service bulletins.

ECU Cold Start Injector Control

On most TCCS engines, an alternate ground may be supplied to the cold start injector by the ECU at the STJ terminal. Based on signals from the coolant temperature sensor, the ECU can operate the cold start injector for up to three seconds regardless of the status of the time switch. Maximum coolant temperature for ECU control is 113'F (45'C), above which the cold start injector will not operate from any source.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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