Coughing and Wheezing?

| April 07, 2005

The latest electronic injection systems will also de-rate the engine, reducing fuel delivery, if boost pressure drops, and the symptom is often a lack of power rather than smoke. However, a failed boost sensor, one that indicates boost pressure that’s higher than what’s actually there, can cause black smoke. This problem will normally result in an engine check light and appropriate trouble codes stored in the electronic control module. A fuel temperature sensor sending a reading that’s warmer than the actual fuel temperature can also cause smoke. You want to inspect wiring and connections to such sensors if you get this kind of symptom or trouble code.

Earlier injectors, such as those used with traditional hydromechanical fuel systems, may need to be rebuilt periodically. Pop pressure, spray pattern, fuel delivery, and nozzle needle lift can be checked on a test stand and the unit overhauled by a diesel specialist. The same checks, minus fuel delivery, will help injection nozzles used with in-line pumps.

Cummins PT injection pumps need to be calibrated on a flow bench periodically. But both these and traditional in-line injection pumps are subject to tampering. PT pumps can have manifold pressure control settings modified for faster response or the Button changed to up the power rating when the turbo and other engine parts are not up to it. In-line pumps can have the manifold pressure control settings or the rack settings changed. Manifold pressure control tampering creates smoke only when you hit the throttle. Incorrect rack settings or the wrong Button will produce smoke whenever the engine is under load. Getting an injection pump re-calibrated is not especially expensive, and correcting these settings will help your engine and oil last longer, and it will improve fuel economy.

In a few cases, internal problems with in-line pumps or unit injector pumps may cause smoke, though the normal result of wear on this equipment is reduced fuel delivery and power.
With the Detroit Diesel Series 92, tampering would consist of altering the settings on the throttle delay or fuel modulation system, or installing injectors that provide more fuel than the original ones. Get a diesel injection specialist to check injector sizes if the engine smokes constantly, or recalibrate the throttle delay/fuel modulator if smoke shows up only at sudden throttle opening.

Backpressure can result if you install the wrong muffler or up-rate the engine when the existing muffler lacks the necessary capacity. An EGR valve that has stuck open might also cause the problem, but you’d get the applicable trouble code. Burnt valves might also be a cause, and they’d likely also cause irregular running and a chugging noise. Have a cylinder pressure test done at an engine shop. Low cetane fuel might be responsible – consider that if the problem shows up suddenly after refueling, especially if changing suppliers.

White smoke

White smoke comes from fuel or other liquids that go right through the engine without evaporating. One cause could be an engine that runs too cold and needs a new thermostat. Another could be very low cetane fuel or a clogged fuel filter. The latter also gives slow throttle response.

Low compression on one cylinder might give puffs of white smoke, but you’d feel rough running or misfire. If something (for example water in the fuel) should cause an injector tip to break off, the resulting complete lack of proper atomization could give white smoke. Here again, you’d feel misfire and rough running.

Coolant leaking into the cylinder because of faulty injector sleeves or O-rings, a cracked head gasket, or an EGR cooler with internal piping that has corroded through could also cause heavy white smoke. Check the radiator or overflow tank for low coolant level.

Blue smoke

Blue smoke means significant amounts of oil are leaking into the combustion chamber. Lube oil burns poorly, it isn’t atomized and properly distributed in the combustion chamber.
This can occur if the turbo drain line is clogged, or if the turbo bearing and seals are worn. Check as described above for oil in the intake system downstream of the turbo. If it’s just turbo trouble, you’ve gotten off easy. However, turbo trouble often indicates oil change intervals have been over-extended, and that makes it all too likely you also have worn piston rings, cylinder liners, main bearings, and valve guides. In this case, you will see a significant loss of oil from the crankcase. A compression, cylinder pressure, or blow-by test at an engine shop will confirm or disprove this possibility.

Heading off trouble

Smoke, like other engine troubles, usually results from a lack of maintenance. On earlier engines, tampering to improve performance is a frequent cause. Don’t tamper with the engine. If somebody already has, get the injection pump or other fuel system parts set to spec’.
You should also change oil and filters as the factory recommends, or at intervals determined by an oil analysis program. Use quality fuel filters and air cleaners, and replace at recommended intervals. Have overheads adjusted as recommended, and get hydro-mechanical injection pumps set to spec’ as frequently as recommended, too. Watch for leaking air intake parts, and go over wiring to make sure insulation is sound and connections are tight. As the engine accumulates high miles, replace electronic injectors when they wear out. Doing all this will head off smoke trouble most of the time.

The right muffler means not only peace and quiet, but also peace of mind

Think of yourself standing waist deep in the ocean at the seashore and being hit by a wave. This is something like what a muffler does to interrupt sound waves in the exhaust. As the exhaust flows around various baffles and through holes inside the muffler, the sound waves are broken up, greatly lowering the volume you hear.

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