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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
Valve Clearance Check: Verify and adjust valve clearances as necessary. If they’re within spec, proceed to Step 2.
Engine Warm-Up: Run the engine until the coolant temperature reaches between 88-96°C (190-205°F).
Test Setup
Battery Prep: Disconnect the battery and connect a charger following OEM guidelines.
Remove Rocker Arm Covers
Disconnect Fuel System Wiring:
Disconnect the fuel injector wiring harness and electrical contacts.
Disconnect the two cable connections to the Jake Brake® solenoid switch.
Injector Harness Removal:
Disconnect the 14-pin injector harness connector.
Remove the spring clip securing the injector harness connector to the camshaft frame.
High-Pressure Fuel Lines: Disconnect from all cylinders.
Injector Removal: Remove all injectors and clear any residual fuel from the cylinders using a vacuum pump.
Compression Testing
Install Compression Adapter: Insert the compression test adapter (J-47411) into the injector holes in the cylinder head.
Secure Adapter: Attach the injector retaining bracket and screws, tightening to 20 Nm (14 lb·ft) + 90 degrees.
Fuel Rail Plug: Install the fuel rail plug (J-48704 or W470589129100).
Reattach Battery: Reconnect the battery with the charger connected to maintain stable voltage.
Note: Sufficient battery voltage is crucial for accurate test results.
DiagnosticLink Setup: Begin the compression test routine using DiagnosticLink to disable fuel supply to the quantity control valve.
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
Remove Test Adapter: Discard injector retaining bolts, remove the compression test adapter, and reassemble components.
Repeat for Suspect Cylinders: Perform the test on each suspect cylinder.
Repairs: Based on test results, perform necessary repairs.
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