Auto Service World
Feature   September 1, 2008   by CARS Magazine

Taking care of diesel engines

Strict adherence to oil changes, fuel cleanliness will help prevent many problems from coming up with diesel engines

Slowly but surely automotive and light-duty truck diesel is making headway in the North American market. According to J. D. Power, the projected percentage of diesel vehicles in North America is expected to reach 15 per cent in 2015, with diesel cars even outperforming hybrid models in light vehicle sales.

Much of this is going to be driven by improvements to diesel technology, some of which is already in the market right now. Taking a spin in one of today’s new diesel cars or trucks, one discovers how different they are from the older diesel technology of the 1970s and early-80s. The engines are cleaner, quieter and more powerful, as well as being very fuel efficient.

For today’s technician, the challenge will be getting up to speed on diesel engines and how to repair them.

Stick to that regular oil change

David Wood, engine specialist with Diesel Auto Services in Vancouver, BC says he has worked with a lot of different diesel engine technologies, most particularly the HEUI (hydraulically actuated, electronically controlled unit injector) diesel engines, one that uses base engine oil pressurized by a high-pressure oil pump to work the injectors.

What Wood says to technicians working on this kind of engine is to pay particular attention to that high-pressure pump and the oil used. As an example, in the 6.0 litre engines, that pump will have to produce up to 4,000 psi of pressure to move the oil to operate the injectors. That puts a lot of strain on the pump, the injectors and most of all on the oil which has to be carefully checked and changed regularly so as to protect the engine components and to make sure the necessary pressures are kept up to keep the engine running properly.

“If you go by the recommended manufacturer’s specifications, they will call for 12,000 km intervals for changing the engine oil,” Wood says. “We at the shop actually recommend even more regular servicing. Engine oil is relatively cheap as compared to (engine) components.”

Another tip with such engines is to regularly use an anti-foam additive when changing the oil. Wood says because the engine system needs to generate high hydraulic pressures to actuate the injectors, it is important to make sure there is no air in the system as air contamination will affect the timing and the precise injection of the fuel.

Andy Vandriel, a mechanic anic with Wayne Pitman Ford Lincoln in Guelph, Ont. says sticking to regularly mandated oil changes is critical to maintaining diesel engines, either in light trucks or automobiles. Too often, according to Vandriel, some owners try to save some money by either forgoing an oil change or pushing an oil change past the recommended interval. The problem when this is done, and which he has seen, is the oil will soon get dirty and break down and then quickly start plugging up the injectors. Telltale signs that contaminated oil, or oil that has bro- ken down, will include hard starting, reduced engine performance and poor fuel economy, adds Vandriel.

As well, the other crucial piece of equipment that has to be carefully maintained is the fuel filter. Vandriel recommends the fuel filter be changed every 24,000 km.

“The filters will get clogged with all sorts of debris,” says Wood. “If that happens (clogging due to debris) you will wind-up with a low transfer pump pressure and when that happens, the drop in pressure will not adequately charge the injection system and you could wind-up with poor fuel economy because you are not burning the fuel quite as well. After a time you could damage the injection components.”

Wood says that, for example, that in Dodge trucks with 24-valve engines, the injection pump is very sensitive to transfer pump pressure and if something happens to the pressure and it drops past a certain point, it could very well cause an overheating condition inside the injection pump and cause it to fail.

Fuel contamination

Sean Bennett, program coordinator with the diesel and truck department at Centennial College in Toronto says one of the big issues with diesel engine maintenance is proper fuel handling. Before, contamination with diesel fuel was a regular problem. Today, it has become less so, but it is still something that technicians should watch out for. When a technician discovers that there is fuel contamination, the likely source is at the facility that has sold the customer the fuel due to poor storage practices.

But sometimes the contamination can come with how a technician handles the replacement of the fuel filter, priming the filter with poor quality fuel or doing it improperly and causing contamination to occur.

“Most manufacturers have taken measures to prevent technicians from (contaminating) a fuel system by the removal of the fuel filter,” says Bennett. “When you put a fuel filter on, in order to maintain prime, the practice was to fill that filter with fuel and the routing geometry of a fuel filter was that the fuel enters from the outside annulus, the upper ring of the filter, and passes through the filtration media and exists through the central bore.”

The proper way to do it is for a technician to pour the fuel through that outer annulus and wait some 15 minutes or more for the fuel to pass through the filtration media. However, some people rush the process and don’t wait for the fuel to pass through before putting the filter in the vehicle. If this is done, there is a good chance for contamination to occur and if that happens, even a 20-30 micron sized particle can cause havoc in the system, adds Bennett, especially in the new common rail diesel engine technologies where if contamination occurs it can plug up key orifices in the common rail system and lead to injector failure.

Common rail diesel

In order to meet today’s stringent emissions standards, diesel engine developers have moved to common rail diesel. Common rail diesel uses a high-pressure fuel rail that feeds individual solenoid valves instead of the older technology where a fuel pump was used to feed unit injectors. As well, today’s common rail diesel engines use piezoelectric injectors to produce more precise fuel pressure and more accurate fuel spray for cleaner burns of fuel. Because common rail systems work on very exacting tolerances and the injectors need to work precisely, technicians will have to pay particular attention to maintaining the injectors and electronics. As well, the high-pressure pipes in the system have to be carefully inspected to make sure there is no damage or leaking. Another thing that will have to be kept in mind is that common rail diesel is especially sensitive to fuel contamination and technicians and manufacturers recommend that owners stick to using ultra-low sulfur diesel fuel which is made to help diesel engines meet today’s emissions requirements. Anything else will cause problems for the engine.



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