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Black Diesel Smoke



Black smoke from a diesel is caused by a too-rich air to fuel ratio. This can be caused by numerous things, including but not limited to: dirty air filters, clogged muffler, catalytic converter, or a diesel particulate filter; as well as a turbocharger malfunction.  Leaky or stuck injectors can cause this also. The addition of chips or tuners, can also adversely affect the amount of Black Diesel Smoke seen.  Smoke can also be caused by advanced or retarded injection timing, but most diesels do not get out of time very often.

Air Filters

Most diesel powered vehicles made in the past 30 or so years have what is called an air filter minder. The minder is mounted post air filter and is able to measure the intake's restriction, or vacuum and when the filter begins to become clogged, triggers a little ball or marker. In the case with Ford diesels, a little plunger pulls out and locks at 25%, 50%, 75%, and 100%, respectively. Never trust the owner's manual on the air filter change schedule. Always change the filter when ever the marker, or whatever your engine happens to be equipped with, tells you it's time to change it. A dirty air filter can most indeed cause excessive black smoke as well as high EGTs and low miles per gallon. In extreme cases it can collapse the filter and the engine will suck the dirt that the filter trapped into itself, quickly destroying the piston rings. In short, keep your filters changed!

Clogged Muffler/ Catalytic Converter

Rarely will a muffler become clogged with soot, exhaust flow will almost always keep carbon deposits (black smoke) from accumulating to the point of clogging the muffler.  More commonly, the Catalytic Converter will clog with partially converted soot (ash) and become in-effective at reducing emissions and become a great restriction in the exhaust system as well.    If your truck is smoking and you suspect the catalytic converter, remove it and inspect.  It will usually be obvious if it is clogged or not.  If not under warranty, replacing the Cat. can be quite expensive.  It is illegal to cut out the catalytic converter, and the offense is punishable by federal law, so use your own judgment if you decide to remove it.   In most states you can easily get away with removing the muffler off of your truck, as the Turbocharger muffles at least 1/3 of the actual sound output of the engine and the Catalytic Converter also muffles the exhaust quite a bit.   Sound levels with the Cat. still in place are about the same if not a bit quieter than a Stock Ford Mustang GT.

Boost Problems

Boost problems causing black smoke can be caused by several things, including but not limited to a faulty turbocharger, leaking intercooler, leaking turbo charge pressure hoses/clamps, holes in the hoses, stuck open wastegate and a host of other possible causes.

Before we tread any further here, I must state, that if your diesel is electronically controlled, most manufacturers have the computer set to defuel if it senses no boost. If you have a  problem, the engine will defuel, and will not make power, but will also not smoke. This, however, is not true for mechanical diesels to a certain point, they use an injection pump with a device which increases fueling with boost, but this device is not 100% accurate all the time.

Typically, if you have a Faulty TurboCharger, the turbo will either, 1. Not Spool (I.e. it's supposed to whistle like no tomorrow) 2. Make Horrible noises because the turbine fins are hitting the housing while it attempts to spool, or if you have had an excessive black smoke issue for a long time, the exhaust side of the turbine, may just have melted to the point that the turbine wheel is no longer effective, however, this is rare, as the Pistons, usually melt before the turbo does.

Keep in mind, if your engine is emitting black smoke continuously while driving, your EGTs are going to be extremely high, and you will do severe damage to your engine by continuing to drive in that condition.  If you look back when you mat the throttle, and you see a very light haze, don't worry about it too much, but if it looks like black death out your exhaust system.. you might want to get it checked.  Also keep in mind, blacks moke, is not only bad for the environment, black smoke is money going out your exhaust that could have made you horsepower, but instead is just making it look like you're on fire.  Some people, actually enjoy laying a thick cloud of diesel soot everywhere.  I've been known to do it occasionally, I have a tuned diesel.

©Brian Hicks 2009  Animated Trucks Provided by

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