GM 6.6L Duramax Diesel V-8 Engines: How to Rebuild and Modify

By the late 1990s, General Motors realized that its old Detroit Diesel engine, which had been designed 20 years earlier, was due for a major update. The Detroit Diesel engine was never intended to be a serious horsepower or torque monster. It was just a steady and reliable workhorse that made credible power, met emissions standards, and achieved decent fuel economy. As Ford and Dodge released new designs of their Power Stroke and Cummins engines, respectively, General Motors needed to follow suit.

The first Duramax engine made its debut in 2001. Over the last 25 years, several versions were introduced, all displacing 6.6L and all producing ever-increasing horsepower, torque, and efficiency. As with any engine that is more than two decades old, many now need a complete overhaul. In GM 6.6L Duramax Diesel V-8 Engines: How to Rebuild and Modify, all aspects of a rebuild are covered in simple step-by-step fashion with more than 375 color photos. A brief history is provided, followed by diagnosis, engine removal, and disassembly procedures, which include the special tools that are required. Next are inspection and machine work, which are followed by reassembly and reinstallation. Finally, a performance chapter is included with commentary by Gale Banks.

Whether you want to tackle this project yourself or just want to know how it all works, this guide will help you along the way.

Table of Contents

Preface 

Acknowledgments 

About the Author 

Chapter 1: History and Operation 

RPO Code 

First Generation (LB7)

Second Generation (LLY)

Third Generation (LBZ)

Fourth Generation (LMM)

Fifth Generation (LML)

Sixth Generation (L5P)

The “Other” Duramax Engines

Engine Identification

Lubrication System

Cooling System

Turbocharger System

Glow-Plug System

Crankcase Ventilation System

EGR Electronic Throttle Valve

The HPCR Fuel-Injection System

Chapter 2: Engine Removal

Chapter 3: Special Tools and Engine Disassembly

Special Tools

Precision Measuring Tools

Valve-Spring Compressor

Electronically Controlled Cooling Fan

Engine Disassembly

Glow Plugs

Chapter 4: Inspection and Machine Work

Engine Block Cleaning, Inspection, and Service

Engine-Mount Hole Thread Inspection

Freeze/Cup Plug Installation

Camshaft and Bearing Inspection

Camshaft Bearing Removal

Oil Cooling Nozzle Removal

Cylinder Bores

Valvetrain Component Inspection 68 Crankshaft and Bearing Cleaning and Inspection

Crankshaft Bearing Selection

Injector Cleaning

Cylinder-Head Disassembly and Inspection

Valve-Guide Measurement, Reaming, and Valve Grinding

Glow-Plug Bores

Balancer

Oil Pan

Intake Manifold

Flywheel Housing

Front Cover

Piston and Ring Inspection

Connecting Rods

Chapter 5: Assembly

Measure the Camshaft Endplay

Engine Oil-Pressure Sensor

Engine Reinstallation

Chapter 6: L5P Engine and Service Issues

2024 L5P Pistons

2024 L5P Head Gasket

2024 L5P Piston Cooling Nozzle

Crankshaft

Cylinder Heads and Valve Springs 105

L5P Turbocharger

L5P Denso Fuel System 2017–Current

Fuel-Rail Pressure Sensor

Fuel-Level Sensor

In-Tank Lift Pump

High-Pressure Fuel Pump

L5P Solenoid Fuel Injector

Piezoelectricity

Fuel Rails

Engine Management

Fuel-Injection Control Module

DTC Retrieval and ECM Communication

Misfire Detection and Cylinder Balance Analysis

Injector Replacement and Calibration Codes

Cylinder Balance Test: Related DTC Not Set

Cylinder Firing Groups

E35 Bosch ECM

Sensor Overview

Exhaust Aftertreatment System

DPF Regeneration

Selective Catalyst Reduction System

Engine Diagnosis Cases

Return Volume Test for High-Pressure System

Duramax Engine Oil Checks

Method to Check for Fluid in Oil

Engine Oil

Oil Filter

Fuel Leaks