Engine Controls - Basic Testing - 6.5L Diesel: Other GMC C3500 HD

Compression

Check engine mechanical condition using a compression gauge, vacuum gauge or engine analyzer capable of performing a relative compression test. If using engine analyzer, see engine analyzer instruction manual for availability and description of relative compression feature.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use a vacuum gauge or a low-pressure (1-5 psi) pressure gauge to check exhaust system.

If using a vacuum gauge, connect gauge to intake manifold vacuum, and start engine. Observe gauge while holding throttle steady at 2000-2500 RPM. If vacuum gauge reading slowly drops after stabilizing, exhaust system may be restricted.

1. Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.
2. Diagnosis

1. Start engine and bring to operating temperature. Increase engine speed to 2000-2500 RPM. Note gauge. Exhaust system is restricted if reading exceeds 1.25 psi (.09 kg/cm 2 ).
2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exists, check for restricted catalytic converter. Replace as required.

DEFINITION

No-start is defined as engine cranks okay but does not start. Engine may fire a few times.

Note. Before performing following tests, check battery condition, engine cranking speed and fuel supply.

SUMMARY

If faults were not found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to appropriate TESTS W/CODES article below. If no hard codes are found in self-diagnostics, or vehicle does not have a self-diagnostic system, proceed to TESTS W/O CODES - 6.5L DIESEL article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

1. «TESTS W/CODES - 6.5L DIESEL»(ref-20088) (for C/K Pickup, Sierra Pickup, Suburban, Tahoe & Yukon)
2. «TESTS W/CODES - 6.5L DIESEL»(ref-20089) (for "P" & "G" Series Van)

Wiring Diagram ("C" & "K" Series Pickup, & Sierra - Diesel VIN F & P With M/T - 1 Of 2). Scheme 118

Wiring Diagram ("C" & "K" Series Pickup, & Sierra - Diesel VIN F & P With M/T - 2 Of 2). Scheme 119

Wiring Diagram ("C" & "K" Series Pickup, & Sierra - Diesel VIN P With 4L60-E - 1 Of 2). Scheme 120

Wiring Diagram ("C" & "K" Series Pickup, & Sierra - Diesel VIN P With 4L60-E - 2 Of 2). Scheme 121

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - Diesel VIN F & S With 4L80-E - 1 Of 2). Scheme 122

Wiring Diagram ("C" & "K" Series Pickup, Sierra, Suburban, Tahoe & Yukon - Diesel VIN F & S With 4L80-E - 2 Of 2). Scheme 123

Wiring Diagram ("P" Series - 6.5L VIN F - 1 Of 2). Scheme 124

Wiring Diagram ("P" Series - 6.5L VIN F - 2 Of 2). Scheme 125

Wiring Diagram ("P" Series - 6.5L VIN Y A/T). Scheme 126

Wiring Diagram ("P" Series - 6.5L VIN Y M/T). Scheme 127

Wiring Diagram (Pickup, Sierra Pickup & Van - 6.5L VIN P - 1 Of 2). Scheme 128

Wiring Diagram (Pickup, Sierra Pickup & Van - 6.5L VIN P - 2 Of 2). Scheme 129