🧠 Mastering Diesel Injector Testing: The Ultimate Guide to Armature Lift, AHE, ZME & More.

Unlock better diagnostics, cleaner emissions, and longer injector life with these expert insights.

🔩 What is Armature Lift?

Armature Lift is the actual displacement (in micrometers, μm) of the injector’s internal armature when the electromagnetic coil is energized.

• It determines how far the needle valve opens, directly affecting fuel delivery and spray pattern.

• Typical value for Bosch CRI3.4: 32–38 μm

  • ❗ Below 30 μm: Poor fuel injection

  • ❗ Above 40 μm: May cause leakage or wear

🧪 Why is Armature Lift Important in Testing?

• Evaluate Opening Efficiency: Too low = poor injection; too high = risk of internal damage

• Diagnose Mechanical Condition: Detect stuck movement, spring tension issues, or contamination

• Verify Refurbishment Quality: Confirm lift is within acceptable range after overhaul

🧲 Advanced Features: AHE & ZME Functions

AHE Function (Activation of Holding Electric Current)

• 📦 For Bosch CRI2 injectors

• Simulates holding current to verify the coil can maintain the open state

• Detects aging coils and intermittent injection failures

ZME Function (Zerstäuber Magnet Einheit)

• 📦 For Bosch CRI3 injectors

• Simulates high-frequency response of spray magnet unit

• Detects slow opening, failed reset, or internal wear

🔍 Key Injector Performance Tests – Explained

Image courtesy of Risey’s testing system

Test	High Value Issue	Low Value Issue	🔧 Solution
WARM	Unstable at high temp	Bad atomization	Clean/Inspect Coil & Valve
LEAK	Seal failure, leakage	Minor seal wear	Replace Seals
VL (Full Load)	Over-injection	Power loss	Check pulse width/control system
VL(R)	Excess return flow	Blocked valve	Clean/replace valve
EM (Emission)	Dirty spray, high NOx	Weak combustion	Clean/replace injector
LL (Low Load)	Too rich at idle	Poor idle or stalling	Adjust pulse, clean injector
VE (Pilot Injection)	Knock, rough engine	Unstable combustion	Inspect nozzle/control system
VE(R)	Return path failure	Weak circuit	Adjust or replace components
VE2	Fuel waste under pressure	Bad startup injection	Check pressure system

🛠️ Extended Load Condition Testing

Condition	Focus	High Value Issue	Low Value Issue
Mid Load	Partial power	High emissions	Weak acceleration
Full Load	Max output	Fuel waste	Engine power loss
Start	Cold ignition	Engine knock	Hard start
Idle	Low RPM	Unstable RPM	Engine stalls

✅ Summary

Proper analysis of armature lift, current-holding capability (AHE), and spray response (ZME), combined with condition-specific fuel flow metrics, offers a complete view of injector health. Whether you're diagnosing faults, refurbishing injectors, or testing with a professional bench, these parameters are key to efficient engine performance and long injector life.