Key diagnostic behavior

In ADEM IV systems, injection is enabled only when two main conditions are met:

• Valid RPM signal (engine speed)
• Sufficient injection actuation pressure (IAP) generated by the HEUI system

If actuation pressure is not reached, the ECM will not trigger injectors, even if all electrical signals are correct.

Critical circuits to verify with this pinout

Injection Actuation Pressure (IAP) control

This is the most critical part of the system.

The ECM controls the IAP through a solenoid (IAP control valve). Failures here can cause:

• No start
• Long crank
• Low power

IAP sensor

The ECM relies on this feedback to enable injection.

A common issue:

• Pressure is present
• But incorrect signal prevents injection

Crankshaft signal

Required for injection timing. Without RPM signal, there is no injector activation.

Injector control circuits

Injectors are activated once RPM and actuation pressure conditions are met. If both are correct but there is no injection, these circuits must be checked.

Power supply and grounds

Stable voltage is required, especially during cranking. Low voltage can affect IAP control and ECM operation.

Practical use of this pinout

This pinout is commonly used to:

• Diagnose no-start conditions related to low actuation pressure
• Verify IAP control solenoid signal
• Check IAP sensor feedback directly at the ECM
• Confirm RPM signal during cranking
• Trace injector control when pressure is present but there is no activation
• Perform bench testing focusing on actuation pressure simulation

Technical note

In HEUI systems like ADEM IV, injection depends on oil pressure, not just electrical command.

Before replacing injectors or the ECM, always verify:

• IAP generation
• IAP sensor feedback
• Control of the actuation solenoid

Misdiagnosis often leads to unnecessary electrical repairs when the root cause is hydraulic.