If you're experiencing a net power loss, odds are good that you've got some sort of boost leak. Diesel engine are simple creatures by nature, but turbo-diesel engines are absolutely dependent upon the turbo itself to make power. Boost leaks are a common fault on older engines, which often develop leaks around the several fittings that link the turbo output to the engine. There's a trick that grizzled, old mechanics use to find boost leaks. Find a friend who smokes really big, cheap cigars and have him blow a thick cloud of smoke around your turbo plumbing; boost leaks will disturb the smoke and send jets of air shooting through it.
Introduced in 1984, the Cummins B-Series engine represented something of revolution in thinking for America's heavy pickup segment. Before a few visionary engineers at Dodge decided to experiment with Cummins' newest light-truck powerplant, big pickups were saddled with unreliable and underpowered and unreliable oil-burners designed for automotive applications. While the industrial-strength Cummins has developed a reputation for power and reliability, no machine works perfectly forever.
Low Sulfur Diesel
The Cummins B-Series engine was designed at a time before the EPA decided to stick its powdered nose into the diesel exhaust industry. In the decades since the Cummins debuted, the government has dropped allowable fuel sulfur levels to less than 10 percent of what they were in 1984. Sulfur's primary job is to act as a lubricant for the engine and fuel pump, reducing parasitic drag and engine wear. Simply getting rid of the sulfur itself can cost power, but there's another side to this equation. Manufacturers use hydrogen injection to remove sulfur, which drops the fuel's cetane rating and its power potential. And worse, cetane rating can vary wildly from pump to pump, from 35 up to 45 depending on the batch and manufacturer.
Fuel Pump Problems
The pre-1998 Cummins' P7100 fuel pump is a fascinating device, resembling nothing so much as a tiny model of the B-Series engine itself. This design makes the pump a fully positive-displacement unit; it always pumps the same amount of fuel regardless of rpm. Fuel pumps, like engines, can and do develop internal leaks over time, depriving your B-series of the required fuel pressure and reducing its power output. As you might have guessed from the previous section, low-sulfur diesel can drastically accelerate pump wear and seal failure. This is especially true where nylon and rubber fittings and seals are concerned, because sulfur helps them to swell and seal more tightly. Low-sulfur diesel can dry fittings, causing them to shrink and release fuel pressure.
Pre-2007 Cummins engines used a wastegate to route exhaust gases around the turbo, bypassing it to control rpm once the turbo had reached optimum boost levels. High exhaust back pressure -- typically resulting from increasing power without replacing the exhaust -- can cause the wastegate actuator to open prematurely. This premature opening will kill midrange torque and throttle response. While an aftermarket wastegate actuator can fix this problem, it doesn't address its root cause. As with all diesel engines, the best modification you can make is to replace the entire exhaust system from the turbo back with one designed for optimal flow. An aftermarket exhaust will not only stabilize the actuator, make more power and increase fuel economy, it'll also drop exhaust gas temperatures to boost turbo and engine longevity.
- AllData: 1997 Dodge Ram 3500 5.9-Liter L6 Vehicle and Engine Specifications
- High-Performance Diesel Builder's Guide; Joe Petitt
- Diesel Power Magazine: Fuel Additive Test - ULSD
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