EVR

Some basic theory to clarify how things work is in order…

The EGR shuts off at Wide Open Throttle (WOT), so it has minimal effect on performance. The addition of exhaust gas drops combustion temperature, increases gas mileage and reduces the tendency of the engine to ping. It can also reduce HC emissions by reducing fuel consumption.

The EGR system has a vacuum source (line from the intake manifold) that goes to the EVR, computer operated electronic vacuum regulator. The EVR is located on the back of the passenger side shock strut tower. The computer uses RPM, Load. and some other factors to tell the EVR to pass vacuum to open the EGR valve. The EGR valve and the passages in the heads and intake manifold route exhaust gas to the EGR spacer (throttle body spacer). The EGR sensor tells the computer how far the EGR valve is open. Then computer adjusts the signal sent to the EVR to hold, increase or decrease the vacuum. The computer adds spark advance to compensate for the recirculated gases and the slower rate they burn at.

Diagram courtesy of Tmoss & Stang&2birds.


The EGR sensor is basically a variable resistor, like the volume control on a radio. One end is 5 volt VREF power from the computer (red/orange wire). One end is computer signal ground (black/white), and the middle wire (brown/lt green) is the signal output from the EGR sensor. It is designed to always have some small voltage output from it anytime the ignition switch is the Run position. That way the computer knows the sensor & the wiring is OK. No voltage on computer pin 27 (brown/lt green wire) and the computer thinks the sensor is bad or the wire is broken and sets code 31. The voltage output can range from approximately .6-.85 volt.

EGR test procedure courtesy of cjones

to check the EGR valve:
bring the engine to normal temp.
connect a vacuum pump to the EGR Valve
apply 5in vacuum to the valve.
if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.
if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.
if engine stumbled, connect vacuum gauge to the hose coming off of the EGR Valve
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 5in vacuum?

if not, check for manifold vacuum at the EGR vacuum valve.
if you have manifold vacuum then connect vacuum gauge to the EGR valve side of the vacuum valve and snap throttle to 2500 RPM.
should read about 5in vacuum

I'm having similar problems with my EGR. I just re-installed it today but I'm not sure if it is working properly. Does anyone know if there should be vacuum at the EGR valve at all times? When I disconnected the vacuum line from the EGR valve there was no vacuum there.

No, there shouldn't be vacuum at the EGR all the time. If there was your car would run like sh**. Best way to check the valve itself is with a vac pump as stated in jrichker's post above. You could also try dumping the codes to se if you have any EGR codes. Also, as stated above, the EGR only opens when the computer tells it to, based on certain conditions such as RPM, engine load, engine temp, etc.

The EVR input sources vacuum from the intake manifold, so the input side has vacuum all the times. The output side of the EVR only has vacuum when the engine is in cruse mode or you do the test I described,

well in your original post you ask about the EVR, which jrichker explained applies vaccum to the egr valve based on load and rpms, and always has vaccum applied to itself. However, what you describe in later posts sounds like the charcoal canister. I think you confused everyone, try typing out exactly what your looking for, and check to make sure its spelled out correctly

The answer is...

Under the plastic snap on top of the EVR is a foam filter. In the center of the foam filter is a steel tube. That steel tube has vacuum applied to it anytime the engine is running. Put your finger over the opening in the tube, the EVR quits regulating and sucks the EGR full open. This will cause the engine to stall out and die if you persist in holding your finger over the opening in the tube.

The steel tube is surrounded by the foam for a reason: it sucks air in through the foam to reduce or regulate the vacuum. The only way to reduce vacuum in a closed system it to admit air. The computer measures the vacuum by using the voltage from the EGR sensor to calculate the vacuum and either add more signal to the EVR or reduce the EVR signal.