By Annalloyd Thomason, Vice President/General Manager, NGVi
As more heavy-duty natural gas vehicles (NGVs) roll out into fleets, the cost of maintenance becomes even more critical, yet an often overlooked or undervalued necessity is adequate technician training. Using natural gas as a transportation fuel is more economical—especially in the medium- and heavy truck market—and those favorable economics are the primary driver behind the decision many fleets make to convert to natural gas. However, favorable economics can easily be diminished or wiped out altogether if maintenance costs increase unnecessarily. What can cause this increase? Typically, it’s a lack of technician training.
Not understanding how to diagnose technical problems on a natural gas vehicle can cost thousands of dollars per vehicle. Maintenance costs can also be increased because fuel system component failures caused by improper maintenance are not covered under warranty.
Medium- and heavy-duty NGVs are very different from diesel vehicles, and technicians must be trained on the properties and characteristics of the fuel itself as well as the fuel system. First and foremost, natural gas is a gaseous fuel—not a liquid—and it does not behave like diesel. Perhaps the most significant difference for technicians to work with is the fact that natural gas ignites via spark ignition, not compression ignition, and the fuel is harder to ignite than diesel. In addition, high-pressure fuel systems on heavy-duty CNG vehicles require different safety and service procedures than diesel vehicles.
Many times, the problems that technicians are trying to diagnose are caused in the fuel system and not the engine. For instance, coating of carry-over oil from the fueling station can cause incorrect sensor readings, which results in many different and serious driveability issues. Filter service requirements are different than those most technicians are accustomed to and filters may not catch ALL the oil in a fuel system. Improper engine oil selection and service intervals can cause engine component failure. And improper coolant service and fill procedures can cause both driveability issues and components failures.
So what are the major issues that technicians usually are not trained to address? Oil carryover is perhaps the single most serious issue and can cause multiple problems, including stumble on acceleration, lack of performance and misfires. Misfires cause overheating of the convertor regardless of the root cause. Contamination, lowering catalyst efficiency, can lead to clogging, increased exhaust backpressure and power loss. In extreme cases, vehicles become nearly undriveable. When compressor oil is present in fuel, it can result in pre-ignition, detonation and engine damage. Technicians must understand these problems and more importantly, how to diagnose and repair them.
Other common problems might include hard starting, too frequent spark plug replacement and poor fuel economy. Technicians must be trained on the NGV ignition system operation and diagnosis. They must fully understand voltage drop analysis and diagnosis—often a weak point for traditional diesel technicians. And they must be trained on determining the root cause of misfires and how to diagnose them.
If technicians are not adequately trained, there are serious economic impacts. First, if technicians don’t know how to diagnose root problems, they usually replace an entire component. This is expensive and unnecessary. The parts most frequently replaced due to the lack of training include spark plugs, fuel and exhaust sensors, coalescing filter elements and three-way catalytic converters. This may not sound too serious at first, until you consider that each three-way catalytic converter on the Cummins ISLG engine series costs about $23,000.
Investing in technician training for medium- and heavy-duty NGVs is just that—an investment that helps protect the long-term favorable economics of using natural gas vehicles. Proper training reduces maintenance cost, reduces vehicle downtime as well as increases technician safety and confidence. And in the long term, it’s an investment with a very short payback.