air pump and fuel ratio

EGR info:
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 EGR valve and the passages in the heads and intake manifold route exhaust gas to the EGR spacer (throttle body spacer). The computer uses RPM, Load. and some other factors to tell the EVR to pass vacuum to open the EGR valve. 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

Smog pump or Thermactor Air System info
The air from the smog pump has no effect on the O2 sensors fuel/air mixture data. The air to the back of the heads shuts down when the computer switches to closed loop and starts using O2 sensor data.

Yo keep all that stuff on for inspection resons!!! your egr can help reduce detonation at part throttle at cruse speed in high gear(ive never had a problem with that on mustangs but ive fixed many of v-8s that do! your air pump will eat a tiny amount of power but it makes it burn cleaner so i would keep it.

I'd keep the egr if I were you. I dumped my air pump and it hurt nothing. Can't say I gained much either, but it cleans up the engine bay.

yeah, an a/c delete and smog pump delete and there is a ton more room to work and makes engine bay look a lot better

keep the EGR but lose the air pump if you live in a state without inspection. i got rid of mine in favor of a UPR polished delete pully, matches my underdrives nicely. (mine locked up thats why i replaced it with the UPR eliminator)