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The Evil Of EGR On Diesel Engines

The Terrible Mess Your Engine Has To Endure For Cleaner Emissions

David Kennedy
May 1, 2011
Photographers: Christian Hazel
Your engine’s manifold absolute pressure (MAP) sensor is your little buddy. Buried somewhere in the stream of your charged intake air (usually in the manifold), it employs a little ceramic or silicone element that senses variations in manifold pressure. The pressure changes indicate engine load, boost, operational elevation, and other pressure variables your ECU needs to know about to get your diesel to run at peak performance.
Photo 2/5   |   1105dp The Evil Of Egr On Diesel Engines installed Map Sensor
But if your MAP sensor is your buddy, your exhaust gas recirculation (EGR) valve is the bully with the huge forehead who stole your lunch money and pants’d you in front of the cheerleaders. In a gasser, EGR isn’t too obnoxious because gas engines don’t create much soot. But in a diesel, well, we’re sure we don’t need to tell you about all the gritty, dirty carbon that little EGR bully throws back through your intake, cylinder head(s), and combustion chamber.
Photo 3/5   |   Don’t try to adjust your TV screen. The blurry, fuzzy, round, black piece is the MAP sensor element in our 6.7L Cummins-powered Ram engulfed with hairy soot from the engine’s EGR system. Owners of ’03½-and-newer Power Stroke, ’04½-and-newer Duramax, and other EGR-equipped diesels can expect the same fate for their MAP sensors.
If your diesel is saddled with an evil EGR system and you’re suddenly noticing your mileage plummeting and your performance suffering, do yourself a favor and pop off your MAP sensor to make sure it’s not coated in a nasty, gooey, sheathing of soot. Our ’07 6.7L Cummins was. It took about 5 minutes to remove, clean, and reinstall our MAP sensor in our Dodge Ram. The reward was a small bump in fuel economy (about mpg) and much snappier throttle response and top end pulling power.
Photo 4/5   |   We simply sprayed our MAP sensor clean with special CRC Mass Air Flow sensor aerosol cleaner from our local auto parts store, but any electrical parts cleaner should work. Try to avoid using harsh brake parts or carburetor cleaner, as they may damage some plastics or sensitive parts.
What Is EGR?
Exhaust gas recirculation (EGR) is a system that takes exhaust gas from a diesel’s exhaust manifold and reintroduces it into the intake of the engine to reduce the combustion chamber temperature.
Why do modern diesels have EGR? you ask. Basically, EGR is used to reduce the formation of NOx emissions, which are created when the combustion chamber temperature exceeds 2,370 degrees. Pumping exhaust (EGR) back into the engine helps to cool the combustion chamber because EGR has almost no oxygen in it. Without oxygen, the temperature stays below the NOx-producing threshold, and the emissions coming out the tailpipe are cleaner.
Unfortunately, the EGR gasses from a diesel tend to bring a sooty mess with themit’s a lot like cholesterol in your body. That sooty mess tends to gum up the EGR valve, EGR cooler, intake ports, and any sensors that are exposed to it. Take a look at these two 6.0L Power Stroke EGR valves. The one on the right is almost new, and the one on the left is so gummed up from EGR that it stopped working. And keep in mind, that as bad as EGR is, if your diesel is tuned to blow black smoke out the exhaustyour EGR system is being exposed to that same stuff!
Photo 5/5   |   1105dp The Evil Of Egr On Diesel Engines egr Valves

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