Metro’s entire fleet of hybrid buses has faulty engines that sometimes fail to start.
“It started at the beginning of their service life, but it has really manifested itself across the fleet in the last six to eight months,” said Phil Wallace, Metro’s general superintendent for bus maintenance and engineering. “In the last three months, we put our finger on it.”
The flawed engines are responsible for the hybrid’s high engine-failure rate compared with the agency’s other new buses. Metro’s 50 hybrids, which were rolled out in 2006, had a 26 percent failure rate in January, compared with a 7 percent failure rate for the agency’s compressed natural gas buses and a 5 percent rate for clean diesel buses, new data shows. The statistics were compiled for the first time at the request of the board of directors.
Wallace said the microcomputer embedded in the engine of each of the hybrid buses was not properly sealed by engine manufacturer Cummins Engine Co. The computers, which measure the engines’ exhaust back pressure and temperatures, have been malfunctioning when the buses are exposed to heavy rain or pressure washing. Moisture slowly seeps into the computer, triggering the check-engine light and causing the engine to cut off while the bus is running its route, Wallace said.
Metro has to find another bus for passengers and dispatches a service car to the bus to reset the system.
“It was a design issue with this model,” he said. “It passed all their testing, but their testing wasn’t rigorous enough.”
Metro has ordered 203 more hybrid buses, which are scheduled to arrive beginning in September, but Wallace said the manufacturer is correcting the problem. Cummins is scheduled to deliver new, properly sealed computers for Metro’s current stock of hybrids at the end of the month and will install them shortly afterward, he said.
Metro staff members have seen the testing data for the new computers and are satisfied with the methods and results, Wallace said. The bus engines are still under manufacturer warranty and Metro will not pay for the replacement equipment. Each General Motors Hybrid bus costs at least $130,000 more than compressed natural gas or clean diesel buses, but are considered more fuel-efficient and environmentally friendly.
Unlike compressed natural gas buses, hybrids can be stored in regular bus depots and require no expensive facility conversions.
“They’re cost-effective to operate,” Wallace said. “Other than this issue, the buses have performed very well since they’ve been in service.”
Bus breakdowns
January bus failure rates by cause
» Hybrid
Engine: 26 percent
Air system: 4 percent
Transmission: 2 percent
Doors: 0 percent
Brakes: 2 percent
» Compressed natural gas
Engine: 7 percent
Air system: 2 percent
Transmission: 2 percent
Doors: 0 percent
Brakes: 0 percent
» Clean diesel
Engine: 5 percent
Air system: 0 percent
Transmission: 2 percent
Doors: 2 percent
Brakes: 1 percent
