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Duramax Fuel System for Dummies

The electronically controlled, high-pressure, common-rail diesel fuel systems of today render most owners lost when attempting to comprehend just what occurs under the hood. Cutting to the chase, not knowing what is and what is not considered normal operation of the Duramax can fuel owner paranoia and bring one to the misconceived notion that a new (and expensive) batch of fuel injectors are needed when, in fact, they are not.

It has not helped that GM historically has demonstrated the inability to produce a reliable diesel fuel injection system. Check that – its first foray into electronically controlled diesel injection pumps on the 6.5 turbo diesel marked that engine forever as unreliable and cantankerous despite the resourceful owners and technicians that have dug in and found reasonable solutions to make the 6.5 more reliable. I still deal with people from the other diesel camps – the Cummins and Powerstoke faithful – who believe that the Duramax is merely a refreshed version of the 6.5 with all its failings: failings that are naturally exaggerated by those who have a prejudice against the General. The common notion that the 6.5 turbo diesel has an unreliable fuel system tainted the Duramax somewhat, especially at the start.

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Typical Four-Stroke Diesel Cycle

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Enter the Duramax in 2001: an amazing engine by all standards that set the pickup diesel market on its ear and left the would-be competition staggering to catch up. Quiet, powerful, efficient, smoke free and – dare we say – reliable? The Duramax made many converts from the other diesel camps simply because it was the best pickup diesel. Combining that engine with a beefy (and still unmatched) Allison transmission in a truck that actually drove and handled like something from the Twenty First Century that we had just entered; well, things were looking up...

...and then the fuel injector debacle began to unfold.

My article in the Spring 2008 issue of maxxTORQUE deals at length with the problems of and solutions to that very well known rash of fuel injector failures in the early days of the Duramax. If you have not read that article, it is well worth your time to go back and get educated on what really was going on at that time. Still, owners tainted by those early problems or rumors of fuel injector failures can have inordinate fears even though real solutions have been implemented.

This brings us to the purpose of this and subsequent articles: to help owners understand the inner workings of their Duramax diesel fuel system. This article will cover the fundamentals of the Duramax common-rail diesel fuel injection system, its components and their normal operation. In a future article, I will look in more detail at the brains of the operation – the Engine Control Module, sensors and control of the fuel system. Future articles will cover diagnosis and repair in more detail for the more adventurous, using tools like EFILive and HPTuners as well as readily available hand-held generic scan tools. This article will arm the average Duramax owner with enough knowledge to begin to understand the normal operation of the fuel system. It is generic enough to cover all Duramax engines, although it should be noted that there are several detailed differences between the LB7, LLY, LBZ and LMM fuel and engine management systems. I will cover each of the major fuel system components, their operation and various common service issues related to each component. To get started, let’s review some points of basic diesel engine operation.