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What are the most common diesel engine repairs?

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Updated 1 Nov 2019

Clinton Brett

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Here, I am talking about failures outside the service schedule, within or outside the manufacturer’s warranty period, and due to poor maintenance. Please DO NOT think that when you’re playing ‘Google mechanics’, any of these repairs are going to fix your diesel.

Working on cars is not viable for the backyard mechanic and diagnosing diesel faults is for the qualified mechanic with years of experience and constant diagnostics training. Replacing the incorrect part can be costly, especially when you have not replaced all the necessary components that are part of the repair.

Fuel system

Fuel system repairs due to poor quality fuel are very common and often I see only the injectors being replaced.
When an injector fails due to normal wear and tear and it has been confirmed that no contamination is present, then you can replace only the full set of injectors. In some cases of normal wear, the entire system will require replacement due to the vital matching of the operating system.

When the system has been contaminated, there is more to the repair than the injectors. In many cases, immediate failure of the fuel injectors is imminent.

At this point, it is good to understand where the fuel travels in the diesel fuel system. From the fuel tank, diesel fuel travels via a fuel filter. A fuel filter will not stop all contaminants from entering the high-pressure system. Too much contamination eventually breaks through and when you decide to fill up with the wrong or poor-quality fuel, this contamination gets through the filter instantly.

From the filter, fuel travels to the high-pressure pump and on to the rail, some fuel from the pump returns to the tank for cooling purposes. Four-cylinder will have one rail, while a V6 and a V8 configuration will have two rails. The rail distributes fuel to all the injectors.

Fuel that is not injected into the engine returns to the fuel tank. Contaminants can become lodged within the metal internals of the pump, rails, pipes and in the tank, in addition to the possibility of rust forming. Once these components begin to break down, the entire system MUST be replaced. No magic chemical cleaner will fix this.

Exhaust gas recirculation valves

Exhaust Gas Recirculation Valves (EGR) and EGR coolers experience very high temperatures during the removal of harmful emissions from the exhaust. Carbon builds up causing the EGR to stick, and if not maintained correctly, prematurely fail. I do not condone so-called preventative maintenance ‘on vehicle intake cleans’ as they damage components, particularly EGR valves, EGR coolers, turbos, and diesel particulate filters (DPFs). In some cases, it can even lead to a complete engine failure.

I’ve seen an average of 50 failures per year from this process. To extend the life of your diesel engine, I advise that you have your mechanic remove the entire intake, EGR and cooler assembly for a full clean using an ultrasonic bath method.

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Written By

Clinton Brett

Clinton Brett is a qualified Heavy Vehicle Mechanic and Diesel Fuel Injection Specialist.

In 2013, he established Diesel Help Australia, an innovative business providing cost effective diagnostic and repair solutions for the automotive industry.

DHA delivers on-vehicle common rail diesel diagnostic training across Australia to the light and heavy industries.

Clinton is a Technical Writer for The Automotive Technician, Australian Workshop Manager and Australian Diesel Mechanic Magazine, as well as the Diesel Guest Speaker for the AAAA Conventions for the last 3 years.