/How to Replace a Car’s EGR Valve

How to Replace a Car’s EGR Valve

Most engines have an exhaust gas recirculation (EGR) valve to help pre­vent the formation of oxides of nitrogen (NOx). NOx in the presence of sunlight forms smog.

Cars EGR Valve at How to Replace a Car’s EGR Valve

As fuel burns, temperature inside an engine can rise to a point at which it acts as a catalyst for nitrogen and oxygen molecules to fuse and form NOx. The EGR valve is used to divert exhaust gas to the cylinders. This gas, being relatively cool, keeps heat in the cylinders below the crit­ical point at which fusion occurs.

A faulty EGR valve will introduce exhaust gas prematurely, diluting the strength of the fuel mixture in the cylinders. A lean fuel mixture de­grades engine performance. Exhaust gas leaking into the cylinders causes an engine to idle rough and also causes one or more of the other perfor­mance problems.

The weakest component of an EGR valve is an internal diaphragm that pulsates to meter exhaust gas to the cylinders. This rubberized part can develop a crack through which exhaust gas will enter the engine when it isn’t supposed to. Here’s how to determine whether this is what has happened and, if so, what to do about it:

Locate the EGR valve. It is usually under the carburetor or throttle body, on the intake manifold, or behind the air meter of an engine equipped with a multiport injection system. If you can’t find the valve, ask a mechanic to point it out.

If the valve is raised high enough off the engine, make sure the en­gine is cold to avoid burning yourself and touch the bottom of the valve to establish whether its diaphragm is exposed. If the di­aphragm is exposed, the bottom of the valve will feel soft and flexible. If the diaphragm is concealed, the bottom of the valve will be metal.

If your EGR valve has an exposed diaphragm, buy a spray can of car­buretor solvent. Start the engine and let it idle. Obviously, the idle will be rough. If it wasn’t, there would be no reason to suspect that the EGR valve was shot. Remember that the one performance problem that pre­vails with a faulty EGR valve is rough idle.

Aim the can of solvent at the underside of the valve and spray the exposed diaphragm. If the diaphragm has a crack, the solvent will seal it and engine idle will become smooth, thus confirming that the EGR valve should be replaced.

To test an EGR valve with a concealed diaphragm, follow these steps:

  • With the engine turned off, disconnect the hose from the EGR valve vacuum fitting.
  • Attach a hand-held vacuum analyzer to the fitting.
  • Pump the handle of the vacuum analyzer until you encounter re­sistance and get a reading on the meter. Watch the meter for about 60 seconds. If the needle drops, the diaphragm is damaged. Replace the EGR valve.
  • If your engine appears to be equipped with a backpressure EGR valve, remove the valve from the engine.
  • Place the base of the valve on a piece of cardboard and trace its outline to make a template.
  • Cut out the template and punch holes in it that coincide with the positions of the bolt holes in the valve.
  • Coat both sides of the template with chassis grease, which you can buy from an auto supply store.

Cars EGR Valve 5 at How to Replace a Car’s EGR Valve

  • Place the template on the engine in the spot occupied by the EGR valve, put the EGR valve on top of the template, and bolt the valve and template to the engine.
  • Start the engine. Has rough idle disappeared? If so, the EGR valve is bad. Install a new one.

To replace a damaged EGR valve, make sure the engine is turned off. Remove the bolts holding the valve to the engine and take off the valve.

Stuff a rag into the hole left in the engine to prevent dirt from falling inside. Then, use a wire brush to clean around the hole. Re­move the rag and install a new EGR valve, using a new gasket. Tighten bolts securely.

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