Detroit Diesel GHG17 Heavy Duty Mechanical Cylinder Compression Test Guide

This guide details how to conduct a mechanical cylinder compression test on a Detroit Diesel GHG17 Heavy Duty engine. Perform this test only when directed by a diagnostic procedure.

Related Tools and Equipment

• Diagnostic Software: DDDL 8.20 (2024)
• Adapter: Nexiq USB Link 3

Prerequisite Check

Start with a relative cylinder compression test using DiagnosticLink. If results suggest a weak cylinder, proceed with this mechanical test.

Mechanical Compression Test Procedure

Preparation

1. Valve Clearance Check: Verify and adjust valve clearances as necessary. If they’re within spec, proceed to Step 2.
2. Engine Warm-Up: Run the engine until the coolant temperature reaches between 88-96°C (190-205°F).

Test Setup

3. Battery Prep: Disconnect the battery and connect a charger following OEM guidelines.
4. Remove Rocker Arm Covers
5. Disconnect Fuel System Wiring:
   • Disconnect the fuel injector wiring harness and electrical contacts.
   • Disconnect the two cable connections to the Jake Brake® solenoid switch.
6. Injector Harness Removal:
   • Disconnect the 14-pin injector harness connector.
   • Remove the spring clip securing the injector harness connector to the camshaft frame.
7. High-Pressure Fuel Lines: Disconnect from all cylinders.
8. Injector Removal: Remove all injectors and clear any residual fuel from the cylinders using a vacuum pump.

Compression Testing

9. Install Compression Adapter: Insert the compression test adapter (J-47411) into the injector holes in the cylinder head.
10. Secure Adapter: Attach the injector retaining bracket and screws, tightening to 20 Nm (14 lb·ft) + 90 degrees.
11. Fuel Rail Plug: Install the fuel rail plug (J-48704 or W470589129100).
12. Reattach Battery: Reconnect the battery with the charger connected to maintain stable voltage.

Note: Sufficient battery voltage is crucial for accurate test results.

13. DiagnosticLink Setup: Begin the compression test routine using DiagnosticLink to disable fuel supply to the quantity control valve.
14. Perform Compression Test:
    • Start the engine with the starter at 150 RPM or higher.
    • Perform five compression strokes and record the gauge reading.
    • At normal operating temperatures, compression should be at least 28 bar (400 psi). If not, repeat with a different gauge to verify.

Note: Injector retaining bolts are single-use only.

Post-Test

15. Remove Test Adapter: Discard injector retaining bolts, remove the compression test adapter, and reassemble components.
16. Repeat for Suspect Cylinders: Perform the test on each suspect cylinder.
17. Repairs: Based on test results, perform necessary repairs.