EGR Valve--whats make it tick?!!

[sprat]

My 95 cavy, 2.2 , has been surging and i checked the EGR valve --its working if i use a vacumn hose and suck on it-the engine decreases the rpm so this shows it working and not defective. I hook the hose from the engine to it and nothing works as i rev the engine up. [ i had used a pencil to plug the end of the hose before to see if this helps any and it runs fine but the mileage sucks.] I sprayed brake cleaner all over the vacumn lines and the engine didnt respond so now i replaced the egr unit that is mounted on the mainfold area with another one from a bone yard--its 35.00 for a new one--although it didnt help any--I FAILED--is there anything else i should be looking for to fix this problem other than buying a new unit at the parts store? Its got me puzzled--i have read in the repair manuals that the engine needs vacumn to operate this or is the electrical unit what controls the EGR? Help please--thanks in advance...

[cujotom]

Buy a new one. If that does the trick great. If not return it. I believe on a 94 cav the egr uses backpressure to operate the vaccum. A new egr costed me about$70 so dont feel bad about $35. I did the same thing went the junk yard route $10 egr valve, still no good, bought a new one and the surge went away.

[ifidie2nite]

Originally Posted by cujotom

Buy a new one. If that does the trick great.

Not something to live by, especially with cars. I'd take it to a shop if it's not the egr and get it diagnosed.

[billyboy128]

Originally Posted by sprat

My 95 cavy, 2.2 , has been surging and i checked the EGR valve --its working if i use a vacumn hose and suck on it-the engine decreases the rpm so this shows it working and not defective. I hook the hose from the engine to it and nothing works as i rev the engine up. [ i had used a pencil to plug the end of the hose before to see if this helps any and it runs fine but the mileage sucks.] I sprayed brake cleaner all over the vacumn lines and the engine didnt respond so now i replaced the egr unit that is mounted on the mainfold area with another one from a bone yard--its 35.00 for a new one--although it didnt help any--I FAILED--is there anything else i should be looking for to fix this problem other than buying a new unit at the parts store? Its got me puzzled--i have read in the repair manuals that the engine needs vacumn to operate this or is the electrical unit what controls the EGR? Help please--thanks in advance...

The EGR system consits of the PCM ,the egr VALVE and various information sensors(ECT, TP, MAP,IAT, RPM and VSS sensors) that the PCM uses to determine when to open the EGR valve. When the PCM closes the power circuit for the EGR valve a Solenoid inside the EGR vale is energized. This creates a magnetic field , which cause a armature to pull up and lift the pintle value off of its seat allowing the exhaust gas to flow fron th exhaust manifold to the intake manifold.

On the 95 Cav 2.2 l OLV the egr value is opened and closed by a seperate control solonoid value, which allows ported vacuum fromn the throttle body to open the EGR valve when told to by the Pcm. the SLOENOID ON THE 95 IS LOCATED ON THE FRONT LEFT of the upper intake manifold to the Left of th throttle position sensor. ( DRIVERS SIDE). It Unbolts from the manifold. YOu can check it to see if its working using a OHM meter( measure resistence), you can also do a vacuum test. The specifics of testing it im not all that sure of. But if its not the EGR value or the vacumm lines this could be causing you a problem.

PS.. A good way to locate the Solenoid is to follow the vacumm line from the EGR back to the throttle body. It runs to the Splenoid.

[billyboy128]

types of EGR valves: the single diaphragm EGR valve. It consists of a spring-loaded diaphragm that is connected to a pintle and seat by a slender steel shaft. Normally closed by spring tension, as it receives ported vacuum, the diaphragm rises, which pulls the pintle off its seat and enables exhaust to flow into the valve's chamber and then on to the intake manifold. To test this component, use a hand-held vacuum pump connected to the vacuum nipple to raise and hold the diaphragm. About eight inches of vacuum should do the trick. The valve should hold vacuum and raise the pintle in a linear fashion. When the engine is idling, pumping it up should stall the engine. This type of valve may or may not have vacuum modulation. Remember, vacuum modulation to the EGR is a vital ingredient of good driveability and precise NOx control. This type of EGR valve is used with a thermal vacuum switch and maybe an inline vacuum delay valve.

The positive back pressure EGR valve can be identified by the letter "P" stamped next to the part number and date code. A back pressure valve is easy to spot because its pintle shaft is much thicker than the single diaphragm type. This is so because the shaft is hollow. The hollow design allows exhaust gases to flow into the shaft and push up on it. When positive back pressure in the exhaust system is sufficient, the shaft raises up and seals the built-in control valve. Once the control valve is closed, it allows applied vacuum to pull up on the diaphragm. Without back pressure to lift the hollow shaft and close the control valve opening, the EGR valve will not hold vacuum. It is bled off to the atmosphere. This design thus modulates EGR flow by modulating the applied vacuum. As engine load increases, so does engine back pressure, which causes the control valve inside the EGR to trap vacuum and open up. To test this valve, bring the engine up to 2,000 rpms to create back pressure, then apply vacuum. EGR should open and cause a 100 rpm drop or more. Exhaust leaks or a modified exhaust system can create havoc here. Adding dual exhaust or headers on a car designed for a single exhaust will reduce back pressure and set a Code 32 on GM cars. Positive back pressure EGR valves are used in simple vacuum controlled systems, as well as more complex pulse width modulated applications. I checked MY EGR valve on my 95 it doesnt have P next to the part number.

EGR solenoids are used with all types of EGR valves 95 (Cavaliers), especially back pressure type valves. The EGR solenoid will have two or more vacuum lines and an electrical connector. The solenoid also has an air bleed and sometimes an air filter. Vacuum is bled off through the filter vent. The PCM uses the solenoid to regulate vacuum to the EGR valve. The vacuum can be manifold or ported vacuum. The solenoid is a vacuum switch with inlet and outlet vacuum ports. The PCM calculates intended EGR flow from various other inputs and then sends a pulsed "on/off" signal to the solenoid. No vacuum flows until commanded by the PCM. This signal turns the vacuum on and off in rapid succession. This is called "pulse width modulation." If the filter becomes clogged, the vacuum cannot bleed off and too strong a signal will be sent to the valve. If that happens, the EGR valve will open too much and cause a driveability problem. The one on your car should be PORTED and theres no filter, as far as I know.

[unbe]

BB128
You know your EGR's,I'm not even having a problem with mine but it's still nice stuff to know.Thanks
Unbe