EGR System

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Overview

The Exhaust Gas Recirculation (EGR) system helps to reduce vehicle emissions by introducing a small amount of exhaust gas into the engine’s intake manifold. Re-burning this used fuel reduces combustion chamber temperatures, which play a huge roll in the formation of dangerous emissions like oxides of nitrogen. EGR failures can be subtle and are usually progressive.
An EGR system starts at the exhaust valve or manifold, where a small channel redirects a certain amount of the spent gases toward the EGR valve. Then, depending on the type of valve, it will be opened by the engine computer, engine vacuum or pressure of the exhaust. Once the valve is open, a predetermined amount of exhaust flows into the intake manifold, and from there into the combustion chamber.

📎 Misfire | Stuck Open EGR | 2011 Subaru Forester
📎 Sticking EGR | Vauxhall Zafira
📝 Misfire Under Load | EGR Passages Clogged | 2011 Toyota Prius.
- Shakes under load while driving. Changed spark plugs, MAF, O2, cleaned throttle body. No change. Took the intake manifold out. Found EGR passages inside the intake were clogged. Cleaning them fixed the problem.
📝 P0402 Exhaust Gas Recirculation Flow (EGR) Excessive Detected | Bad/wrong air filter | 2009 Dodge Ram 6.7L
📝 P1404 EGR Closed Position Performance | PCM Reflash (TSB) | 2001 Chevy Impala 3.8L
📝 EGR Dirty Passages

An EGR valve that fails to close properly can act as a vacuum leak, causing the fuel and air mixture to become too lean, resulting in an engine that sputters and misses at idle. This can also lead to engine stalling and hesitation upon acceleration.

When an EGR valve fails to open and close at the proper rate, at the proper time, overall engine power is reduced due to decreased combustion chamber efficiency. This results in the engine using more fuel to do the same amount of work it would normally do under normal operating conditions. Modern engines also make use of computers that can read this as an incorrect fuel ratio, and instruct the fuel system to compensate by introducing more fuel into the mixture.

The introduction of exhaust gases into the combustion chamber by the EGR valve serves to reduce the temperature of the ignition process. If the EGR valve fails to open, combustion temperatures increase, resulting in higher overall engine temperatures, which can lead to engine overheating.

Pinging and knocking commonly result from increased engine temperatures. These increased temperatures cause pinging and knocking by creating a condition where the fuel and air mixture within a cylinder ignites prematurely. If an EGR valve is opening improperly, it can increase engine temperatures, causing the pre-ignition of the combustion process before the proper timing, resulting in engine knock.

The EGR valve’s main purpose is to aid in the reduction of noxious gases produce by the engine. It does this by lowering the temperature of the combustion process through the introduction into the combustion chamber of controlled amounts of exhaust gases. This lower temperature has the effect of reducing the amount oxides of nitrogen (NOx) produced by the engine. A faulty EGR valve will fail to properly cool the combustion process allowing these gases to increase, which can lead to an abnormally high NOx reading during emissions testing.

The Stall test
- With this test we fully open (by vacuum or electrically) EGR valve to allow gasses to flow intake manifold. Warm up the engine. Apply vacuum and the motor must nearly stall from 800rpm normal idle. I get 400 RPM and a shaking motor, some motors stall. This symptom is a pass (stalling or nearly). If the RPM changes none or little? (a 100 rpm drop is too little), then the path is blocked.