All Fairmont and Zephyr models are equipped with Exhaust Gas Recirculation (EGR) systems to control oxides of nitrogen.
On V8 engines, exhaust gases travel through the exhaust gas crossover passage in the intake manifold. A portion of these gases are diverted into a spacer which is mounted under the carburetor. The EGR control valve, which is attached to the rear of the spacer, consists of a vacuum diaphragm with an attached plunger which normally blocks off exhaust gases from entering the intake manifold. On 4- and 6-cylinder engines, an external tube carries exhaust manifold gases to the carburetor spacer. On all models, the EGR valve is controlled by a vacuum line from the carburetor which passes through a ported vacuum switch. The EGR ported vacuum switch provides a vacuum to the EGR valve when the coolant temperature is above 125°F. The vacuum diaphragm then opens the EGR valve permitting exhaust gases to flow through the carburetor spacer and enter the intake manifold where they combine with the fuel mixture and enter the combustion chambers. The exhaust gases are relatively oxygen-free, and tend to dilute the combustion charge. This lowers peak combustion temperature thereby reducing oxides of nitrogen.EGR System Venturi Vacuum Amplifier
The EGR system also includes a Venturi Vacuum Amplifier (VVA). The amplifier is used to boost a relatively weak venturi vacuum signal in the throat of the carburetor into a strong intake manifold vacuum signal to operate the EGR valve. By matching venturi air flow to EGR flow more closely, driveability is improved.
The amplifier features a vacuum reservoir and check valve to maintain an adequate vacuum supply regardless of variations in engine manifold vacuum. Also used in conjunction with the amplifier is a relief valve, which will cancel the output EGR vacuum signal whenever the venturi vacuum signal is equal to, or greater than, the intake manifold vacuum. Thus, the EGR valve may close at or near wide-open throttle acceleration, when maximum power is needed.EGR/Coolant Spark Control (CSC) System
The EGR/CSC system regulates both distributor spark advance and the EGR valve operation according to coolant temperature by sequentially switching vacuum signals.
The major EGR/CSC system components are:
- 95°F EGR-PVS valve
- Spark Delay Valve (SDV)
- Vacuum check valve
When the engine coolant temperature is below 82°F, the EGR-PVS valve admits carburetor EGR port vacuum (occurring at about 2,500 rpm) directly to the distributor advance diaphragm, through the one-way check valve.
At the same time, the EGR-PVS valve shuts off carburetor EGR vacuum to the EGR valve and transmission diaphragm.
When engine coolant temperature is 95°F and above, the EGR-PVS valve is actuated and directs carburetor EGR vacuum to the EGR valve and transmission instead of the distributor. At temperatures between 82°-95°F, the EGR-PVS valve may be open, closed, or in midposition.
The SDV valve delays carburetor spark vacuum to the distributor advance diaphragm by restricting the vacuum signal through the SDV valve for a predetermined time. During normal acceleration, little or no vacuum is admitted to the distributor advance diaphragm until acceleration is completed, because of (1) the time delay of the SDV valve and (2) the re-routing of EGR port vacuum if the engine coolant temperature is 95°F or higher.
The check valve blocks off vacuum signal from the SDV to the EGR-PVS so that carburetor spark vacuum will not be dissipated when the EGR-PVS is actuated above 95°F.
- Allow the engine to warm up, so that the coolant temperature has reached at least 125°F.
- Disconnect the vacuum hose which runs from the temperature cut-in valve to the EGR valve at the EGR valve end. Connect a vacuum gauge to this hose with a T-fitting.
- Increase engine speed. Do not exceed half throttle or 3,000 rpm. The gauge should indicate a vacuum. If no vacuum is present, check the following:
- The carburetor-look for a clogged vacuum port.
- The vacuum hoses-including the vacuum hoses to the transmission modulator.
- The temperature cut-in valve-if no vacuum is present at its outlet with the engine temperature above 125°F and vacuum available from the carburetor, the valve is defective.
- If all the above tests are positive, check the EGR valve itself.
- Connect an outside vacuum source and a vacuum gauge to the valve.
- Apply vacuum to the EGR valve. The valve should open at 3-10 in. Hg, the engine idle speed should slow down and the idle quality should become more rough.
- If this does not happen, i.e., the EGR valve remains closed, the EGR valve is defective and must be replaced.
- If the valve stem moves but the idle remains the same, the valve orifice is clogged and must be cleaned.
If an outside vacuum source is not available, disconnect the hose which runs between the EGR valve and the temperature cut-in valve and plug the hose connections on the cut-in valve. Connect the EGR valve hose to a source of intake manifold vacuum and watch the idle. The results should be the same as in Steps 6-7, above.Temperature Cut-In Valve EGR Ported Vacuum Switch
- Remove the valve from the engine.
- Connect an outside source of vacuum to the top port on the valve. Leave the bottom port vented to the atmosphere.
- Use ice or an aerosol spray to cool the valve below 60°F.
- Apply 20 in. Hg vacuum to the valve. The valve should hold a minimum of 19 in. Hg vacuum for 5 minutes without leaking down.
- Leave the vacuum source connected to the valve and place it, along with a high temperature thermometer, into a non-metallic, heat-resistant container full of water.
- Heat the water. The vacuum in the valve should drop to zero once the temperature of the water reaches about 125°F.
- Replace the valve if it fails either of the tests.
The vacuum modulator is used only with an automatic transmission.
- Remove the vacuum modulator from the car.
- Connect the modulator to an outside vacuum source: a distributor tester, for example.
The vacuum source should be adjusted to supply 18 in. Hg, with the end of the vacuum line blocked off.
- Connect the vacuum line from the vacuum source to the EGR port on the vacuum modulator.
- The vacuum modulator should hold the 18 in. Hg reading. If it does not, then the diaphragm is leaking and must be replaced.
The amplifiers have built-in calibrations and no external adjustments are required. If the amplifier tests reveal it is malfunctioning, replace the amplifier. All connections are located on one side of the amplifier. A vacuum connector and hose assembly is used to assure that proper connections are made at the amplifier. The amplifier is retained with a sheet-metal screw.
- Operate the engine until normal operating temperatures are reached.
- Before the vacuum amplifier is checked, inspect all other basic components of the EGR System (EGR valve, EGR/PVS valve, hoses, routing, etc.).
- Check vacuum amplifier connections for proper routing and installation. If necessary, refer to the typical vacuum amplifier schematic.
- Remove the hose at EGR valve.
- Connect a vacuum gauge to the EGR hose. The gauge must read in increments of at least 1 in. Hg graduation.
- Remove the hose at the carburetor venturi (leave off).
- With engine at curb idle speed, the vacuum gauge reading should be within +- 0.3 in. Hg. of specified bias valve as shown in amplifier specifications for other than zero bias. Zero bias may read from 0 to 0.5 in. Hg. If out of specification, replace the amplifier.
- Depress the accelerator and release it after the engine has reached 1,500 to 2,000 rpm. After the engine has returned to idle, the vacuum must return to the bias noted in Step 7. If the bias has changed, replace the amplifier. Also, if the vacuum shows a marked increase (greater than 1 in. Hg) during the acceleration period, the amplifier should be replaced.
- Hook up the venturi hose at the carburetor with the engine at curb idle rpm. If a sizeable increase in output vacuum is observed, (more than 0.5 in. Hg above Step 7), check the idle speed. High idle speed could increase output vacuum due to venturi vacuum increase. See the engine decal for the correct idle specifications.
- Check the amplifier reservoir and the connections as follows: disconnect the external reservoir hose at the amplifier and the AP or plug. Depress the accelerator rapidly to 1,500 to 2,000 rpm. The vacuum should increase to 4 in. Hg or more. If out of specifications, replace the amplifier.
Remove the EGR valve for cleaning. Do not strike or pry on the valve diaphragm housing or supports, as this may damage the valve operating mechanism and/or change the valve calibration. Check the orifice hole in the EGR valve body for deposits. A small hand drill of no more than 0.060 inch diameter may be used to clean the hole if plugged. Extreme care must be taken to avoid enlarging the hole or damaging the surface of the orifice plate.VALVES WHICH CANNOT BE DISASSEMBLED
Valves which are riveted or otherwise permanently assembled should be replaced if highly contaminated; they cannot be cleaned.VALVES WHICH CAN BE DISASSEMBLED
Separate the diaphragm section from the main mounting body. Clean the valve plates, stem, and the mounting plate, using a small power driven rotary wire brush. Take care not to damage the parts. Remove deposits between stem and valve disc by using a steel blade or shim, approximately 0.028 inch thick, in a sawing motion around the stem shoulder at both sides of the disc.
The poppet must wobble and move axially before reassembly.
Clean the cavity and passages in the main body of the valve with a power driven rotary wire brush. If the orifice plate has a hole less than 0.450 inch, it must be removed for cleaning. Remove all loosened debris, using shop compressed air. Reassemble the diaphragm section on the main body using a new gasket between them. Tighten the attaching screws to specification. Clean the orifice plate and the counterbore in the valve body. Reinstall the orifice plate, using a small amount of contact cement to retain the plate in place during assembly of the valve to the carburetor spacer. Apply cement only to the outer edges of the orifice plate to avoid restriction of the orifice.EGR SUPPLY PASSAGES AND CARBURETOR SPACER CLEANING
Remove the carburetor and carburetor spacer on engines so equipped. Clean the supply tube with a small power driven rotary wire brush or blast cleaning equipment. Clean the exhaust gas passages in the spacer, using a suitable wire brush and/or scraper. The machined holes in the spacer can be cleaned by using a suitable round wire brush. Hard encrusted material should be probed loose first, then brushed out. On 6-cylinder engines, the external tube from the exhaust manifold must be removed and cleaned with a brush.EGR EXHAUST GAS CHANNEL CLEANING
Clean the exhaust gas channel, where applicable, in the intake manifold, using a suitable carbon scraper. Clean the exhaust gas entry port in the intake manifold by hand, passing a suitable drill bit through the holes to auger out the deposits. Do not use a wire brush. The manifold riser bore(s) should be suitably plugged during the above action to prevent any of the residue from entering the induction system.