SPACER ENTRY EGR SYSTEM
See Figures 1, 2, 3 and 4
In this system, a vacuum operated EGR flow valve is attached to the carburetor spacer. A passage in the carburetor spacer mates with a hole in the mounting face of the EGR valve or the intake manifold. The most common system allows exhaust gases to flow from the exhaust crossover, through the control valve and through the spacer into the intake manifold below the carburetor. For those engines where exhaust gases cannot be picked up from the exhaust crossover (6 cylinder) as described above, the gases are picked up from the choke stove located on the exhaust manifold or directly from the exhaust manifold. The exhaust gases are routed to the carburetor spacer through steel tubing.
The vacuum signal which operates the EGR valve originates at the EGR vacuum port in the carburetor. This signal is controlled by at least one, and sometimes two, series of valves.
A water temperature sensing valve (the EGR PVS) which is closed until the water temperature reaches either 60°F (15.5°C) or 125°F (52°C), depending on application, is normally used.
The position of the EGR vacuum port in the carburetor and calibration of the EGR valve can be varied to give the required modulation of EGR during acceleration and low speed cruise conditions. However, a more complicated system using a second series valve is sometimes needed to provide control of EGR for engine operation at high speed cruise conditions. The second valve, the high speed modulator valve, is controlled as a function of vehicle speed.
The high speed EGR modulator subsystem consists of a speed sensor, an electronic module and a solenoid vacuum valve. The speed sensor, driven by the speedometer cable, provides an AC signal in relation to engine speed, to the electronic module. The electronic module processes the information from the speed sensor and sends a signal to the high speed modulator (vacuum solenoid) valve. When the vehicle speed exceeds the module trigger speed, the solenoid vacuum valve closes which, in turn, causes the EGR valve to close.EGR Valve Cleaning
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 orifice hole in the EGR valve body for deposits. A small hand drill of no more than 0.060 inch; (1.5mm) 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. Clean the cavity and passages in the main body of the valve.EGR Supply Passages and Carburetor Space Cleaning
Remove the carburetor and carburetor spacer on engines so equipped. Clean the supply tube with a small power driven rotary type wire brush. 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.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.EGR System Testing
VALVE FUNCTION TEST
With the engine at idle, apply 8 in. Hg of vacuum to the EGR valve. The valve stem should move opening the valve and the engine should roughen. If the valve stem moves but the engine does not roughen, remove and clean the inlet and outlet ports with a wire brush. Do not use sandblasting or gasoline to clean the EGR valve because they will damage the valve.
With the engine at idle, trap 4 in. Hg of vacuum in the valve and hold it. Vacuum should not drop more than 1 in. Hg in 30 seconds. If so, replace the valve.SEAT TEST
When the valve is suspected of leaking, which is indicated by rough idle or stalling, perform the following:
- Insert a blocking gasket with no flow holes between the valve and mounting base and retighten the valve.
- Start the engine and observe idle quality. If the engine idle improves, replace the valve and remove the blocking gasket.
ELECTRONIC EGR (EEGR) SYSTEM
See Figure 5
The Electronic EGR system (EEGR) is found in all systems in which EGR flow is controlled according to computer commands by means of an EGR valve position sensor (EVP) attached to the valve.
The EEGR valve is operated by a vacuum signal from the dual EGR Solenoid Valves, or the electronic vacuum regulator which actuates the valve diaphragm.
As supply vacuum overcomes the spring load, the diaphragm is actuated lifting the pintle off of its seat allowing the exhaust gas to flow. The amount of flow is directly proportional to the pintle position. The EVP sensor sends an electrical signal notify the EEC of its position.
The EEGR valve is not serviceable. The EVP sensor must be serviced separately.
INTEGRAL BACKPRESSURE (IBP) EGR SYSTEM
See Figure 6
The Integral Backpressure (IBP) EGR system combines inputs of EGR port vacuum and backpressure into one unit. The valve requires both inputs for proper operation. The valve won't operate on vacuum alone.
There are two types of backpressure valves: the poppet type and the tapered pintle type.
PORTED EGR VALVE
The ported EGR valve is operated by engine vacuum alone. A vacuum signal from the carburetor activates the EGR valve diaphragm. As the vacuum signal increase it gradually opens the valve pintle allowing exhaust gases to flow. The amount of flow is directly proportional to the pintle position.Functional Check-Signal Response
Check that all a vacuum lines are properly routed and all connections are secure. If vacuum hoses are cracked, crimped or broken replace them.
- When the engine is cold there should be no vacuum to operate the valve. If there is vacuum check the PVS or TVS for function and replace as required.
- There should be no vacuum at the valve at warm curb idle.