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= EGR Theory. EGR serves one purpose and one purpose only. That purpose is to reduce Oxides of Nitrogen (NOx). Undernormal combustion, Nitrogen(N2)Oxygen (O2) in the air and Hydrocarbons (HC) in the fuel combind into water(H2O) Carbon dioxide (CO2) and the Nitrogen remains unchanged. Under very hot combustion temperatures, the Nitrogen reacts with the other two byproducts and forms Nitrogen oxide (NO). After being released into the atmosphere, it picks up another Oxygen and becomes Nitrogen dioxide (NO2). In the presence of sunlight,

it combines with other compounds like Hydrocarbons and forms Smog. Since exhaust gas is inert (very stable) it doesn't burn again. So by being introduced into

the combustion chamber, it will lower combustion chamber temps enough so that

the Nitrogen doesn't react with the other compounds and is passed unchanged out

the tailpipe thus not contributing to smog. Now, since exhaust gas doesn't burn, it

doesn't exactly help with combustion. At higher RPM's, this really isn't noticable,

but at idle, the reintroduction of exhaust gas will cause a very rough idle and can

cause stalling if to much is introduced into the combustion chamber = = EGR Valve = 4.2L, 4.6L, 5.4L and 6.8L Engines 1. Disconnect the negative battery cable. 2. Remove the vacuum hose from the EGR valve. 3. On the 4.6L engine, remove the nut and brake booster bracket. 4. On the 5.4L engine, remove the DPFE sensor retaining nuts and place the sensor to the side to allow access to the EGR tube. 5. Disconnect the EGR valve-to-exhaust manifold tube from the EGR valve. 6. Remove the EGR valve mounting bolts, then separate the valve from the intake manifold. 7. Remove and discard the old EGR valve gasket, and clean the gasket mating surfaces on the valve and the intake manifold. To Install: 8. Install the EGR valve, along with a new gasket, on the manifold, then install and tighten the mounting bolts. 9. Connect the EGR valve-to-exhaust manifold tube to the valve, then tighten the tube nut to 25-35 lbs. (34-47 Nm). 10. Connect the vacuum hose to the EGR valve. 11. On the 5.7L engine, install the DPFE sensor. 12. On the 4.6L engine install the brake booster bracket and the retaining nut. 13. Connect the negative battery cable.

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