Knock Noise in a Detroit Diesel Series 60

by Richard Rowe
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Introduced in 1987, the first Detroit Series 60 engine was a departure from its predecessors in many ways. Its overhead camshaft increased flow through the head and its drive-by-wire throttle made it the very first roadgoing truck engine to utilize full electronic controls. While the 60's advanced technologies did help to make it a darling among drivers and mechanics for decades, it isn't free of the problems that plague all diesels regardless of vintage or design.

Normal Clatter

The Series 60 isn't the loudest diesel on Earth, but it's still a diesel. Diesels operate in a constant state of detonation, which isn't as precise or as fast as spark ignition. A diesel engine compresses its fuel to ignition rather than quickly flashing it to boom with a spark. All diesels operate under a certain amount of uncontrolled detonation or even preignition, and direct-injection engines like the Series 60 are even more prone to rattle. Add that to the engine's normal fuel injector and fuel pump racket and you've got a recipe for constant, though normal, clatter.

Fuel Knocking

Because the diesel ignites fuel as the piston rises in the cylinder, fuel injected before the piston approaches top dead center will preignite and create a separate flame front. When that flame front smacks into the one that's supposed to propagate from the top of the cylinder, the shockwaves cancel out and result in knock. Ironically, these dual flame fronts will result in incomplete combustion; or at least mistimed combustion, resulting in a misfire.

Fuel Knock Problems

If you haven't modified the engine, then odds are that you've got some sort of fuel leakage in the cylinder. This fuel could come from a leaking injector, but it could just as well be an internal oil leak. The Series 60 is more than capable of using its oil for fuel, so oil leaking into the cylinder through bad seals or through the turbo will act as an additional fuel and incite preignition. Advancing the fuel injection timing or excessively lengthening the injection cycle will also cause preignition, which is why diesel enthusiasts generally prefer to install larger injectors rather than simply playing with the stock injector timing or duration.

Loss of Air or EGR

A lack of boost, uncontrolled boost, a malfunctioning wastegate or a malfunctioning exhaust gas recirculation valve or solenoid will all throw off the engine's delicate air/fuel balance. This is the inverse of a leaking injector; that being just the right amount of fuel, but too little oxygen to burn it. Boost leaks and a malfunctioning wastegate will result in a noticeable drop in boost on your truck's analog boost gauge. Some other oxygen-related failures will trigger a check engine light and others will not, depending upon the model year.

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