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Diesel EGR problems

Exhaust Gas Recirculation (EGR) valves cause more

than their fair share of problems. Problems with theEGR system, like so many vehicle problems, are oftencaused by a lack of maintenance: diesel ownerstypically expect high mileages and low maintenancebills. Because owners expect their diesels to go forhuge mileages without much maintenance, they dontpay much attention to their diesel engines untilsomething goes wrong. By then it may be too late.

Also, many diesel owners resent paying to have theirengines EGR valve replaced at a fairly early age (it canbe expensive). However, faulty EGR valves cansometimes be fixed by simply cleaning them.Moreover, many EGR problems can be avoided bysimply ensuring that the vehicle is maintainedregularly and gets a decent blat down a highway atleast once a month, with plenty of accelerating and

decelerating (pottering around town at low speeds isespecially bad for EGR valves). Many owners have triedto remove the EGR assembly for this reason, but thereare lots of fishhooks in the process. The first one isthat the removal of the EGR assembly will confuse theECU and trigger a check engine light. There are,however, proper removal kits for those who wish totake this path. This removal kit has blanking plates for

the manifold, together with a custom computer chipthat fools the ECU into thinking that nothingschanged.There are lots of reasons for removing theEGR, and lots of reasons for not removing the EGR. TheExhaust Gas Recirculation (EGR) valve is an anti-pollution device, aimed primarily at reducing theamount of nitrogen oxide (NOx) spewing out of thevehicles exhaust pipe. The engine produces nitrogen

as part of the combustion process. As thetemperatures inside the engine increase, this nitrogen

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and the oxygen in the engines combustion chambercan chemically combine to form nitrogen oxides. NOxreacts with sunlight to cause smog. Exhaust GasRecirculation works by recirculating a controlledportion of an engines exhaust fumes back throughthe engine. The EGR valve is the tap that turns the flowof exhaust gases on and off, hopefully at appropriatetimes.These recycled, carbon dioxide-rich exhaustfumes cool the combustion chambers within theengine. This cooling effect lowers the combustionchamber temperature. These recycled exhaust fumesalso displace some of the oxygen that would otherwise

be drawn into the engine from the surroundingatmosphere. Because the combustion chamber iscooler and because theres less oxygen, less NOx isproduced.Also, because the combustion chambers arecooler, the engine as a whole runs cooler. This isparticularly important to the engines turbocharger:turbochargers (and the oil that they need for theirlubrication) dont last long if the engine is

overheating.

Because the EGRs recycled exhaust gasdisplaces some of the air within the combustionchamber, the engines efficiency is reduced. For thisreason, the EGR system doesnt operate during timesof heavy acceleration. It also doesnt operate duringidle, because the presence of exhaust gases at idletends to cause uncontrollable rough running. EGRsystems operate primarily when the vehicle is cruising

under light load. Because there is less demand on theengine when the vehicle is cruising under light load,the engine can afford to temporarily lose somecapacity. Also, because of the cooling effect of the EGRsystem, the engine can run cooler when the vehicle iscruising under light load. Because the engine is cooler,the engines lubricating oil is cooler as well. Cool oillasts longer and works better than oil that has been

continuously overheated. Therefore, the EGR system isimportant for the cool running of the engine and also

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in the protection of the engine oil from continuousheat.In the real world, EGR valves often dont workvery well. What goes wrong is this: the exhaust gasesfrom the vehicles engine contain much more than justcarbon dioxide: they also contain dozens of chemicalby-products, left behind after the fuel was burntinside the engine. One of these by-products is a finedust, known as particulates. This dust is mostlyunburnt carbon fuel. The more efficiently the dieselengine burns its fuel, the less carbon dust isproduced. However, no diesel engine works withanything like complete efficiency and, over time, the

carbon dust inside the exhaust gases begins to clogup the EGR system, reducing the movement of the EGRvalve. This clogged EGR valve causes the engine to runbadly due to an imbalance in the fuel/air mixture.Because the engine is running badly, the fuel is notbeing consumed efficiently. Because the fuel is notbeing consumed efficiently, more carbon dust isproduced. Some of this carbon dust within the exhaust

gets recycled by the EGR system, clogging the EGRvalve still further. The more the EGR gets clogged, themore carbon dust is produced. The more carbon dustis produced, the more the EGR valve clogs. Thisviscious circle continues until the EGR valve jamscompletely open or closed.If the jammed EGR valve isnot repaired or replaced quickly, all sorts of problemsmay occur. Four of the most common are rough

running, high fuel consumption, turbocharger failureand, sometimes, total engine failure. Heres how itworks:When the engine is cruising, the EGR valve issupposed to open to allow the carbon dioxide in theexhaust to cool the combustion chamber. However, ifthe EGR valve jams open, exhaust fumes are being fedinto the engine at all times. This can mean pooracceleration and rough running, because the excess

exhaust fumes are depriving the engine of oxygen.Because there is insufficient oxygen, theres too much

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fuel, so the unburnt fuel starts spewing out of theexhaust as black smoke, especially when the engine isat idle. Fuel consumption is likely to rise substantially.Also, due to a lack of oxygen (which is needed tocomplete the combustion process), the enginesometimes starts to misfire, sometimes seriously (thismisfiring may produce an unusual metallic rattle orknocking when the engine is under load). If the engineis left in this condition for too long, the engine life willbe shortened considerably. In the worst case thisproblem may cause melted pistons and thereforeengine failure. The valves in the cylinder head may

also begin to stick due to being heavily coated withcarbon.However, other really nasty problems occurwhen the EGR valve jams closed: without the coolingeffect of the exhaust gases, the engine starts tooverheat. Over time, this overheating causes theengine oil that feeds the turbocharger to break down.When the engine oil starts to break down, the bearingsin the turbocharger fail. When the bearings fail, the

turbocharger will fail, and replacement wont becheap. If the turbocharger is replaced without solvingthe EGR problem, the next turbocharger will also failbefore too long.It gets worse: when the engineoverheats, more lubricating oil can enter thecombustion chamber and the engine can start runningon lubricating oil even if the diesel fuel supply is cutoff. The engine may then begin to run on its own

engine oil instead of diesel fuel. The driver may beunable to switch off the engine except by stalling it.Eventually, the engine sucks away all the lubricating oiland the engine disintegrates.