EGR Vacuum Regulator

The car will idle like crap with the EGR connected directly to manifold vac (as you have it). The regulator, as you noted, is like a switch for vacuum to the EGR valve. This is how the EGR is actuated at cruise.

It is very much like if you connected your headlights directly to the battery and then wondered why they were on non-stop. Obviously getting them run through the headlight switch (which you manually control vs the EGR reg being controlled by the EEC) would fix the issue.


Good luck.

Here is the basic flow for the EGR system...

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 primary result of EGR usage is a reduction in NOx emissions.

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.




Troubleshooting:
There should be no vacuum at the EGR valve when at idle. If there is, the EVR (electronic vacuum regulator) mounted on the backside of the passenger side wheelwell is suspect. Check the vacuum line plumbing to make sure the previous owner didn’t cross the vacuum lines.

Diagram courtesy of Tmoss & Stang&2birds. (the diagram says 88 GT, but the EGR part is the same for 86-93 Mustangs)


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 2-5 in 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 2-5 in vacuum


Late Model Restoration has the Ford Racing M-12071-N302 kit with the EGR valve & sensor along with the ACT & ECT sensors for $45. See http://www.latemodelrestoration.com/iwwida.pvx?;item?item_no=M12071N302 1&comp=LRS for more details

Prime Lord said:

jrichker, is there anything you DON'T have a diagram for? hehe.

Okay, from what you have there, I think I do still have the EGR vac sensor, but its not hooked up (seeing as how NONE of the things on the backside of the strut tower are). Provided that, the other valves that look similar to the EGR vac sensor have to do w/ the smog pump (which is gone as well) so I need to find out which one of those is for the EGR, hook that up, and ditch the stuff having to do w/ the smog pump? Is that accurate?

The lines that are unhooked right now all go to these square connectors that have 4 prong vacuum connectors....this sucks...vacuum lines will be the end of me.

Okay, so here's what I've got....since I don't have a smog pump, this is what my vacuum lines should look like, correct?


for the EGR stuff at least, I edited out the rest of the graphic

Click to expand...

You are correct.

You won't need the vacuum reservoir or the check valve since the EGR vacuum regulator connects directly to any one of the manifold vacuum sources.

Prime Lord said:

Okay, so I sorted out that. Found that the EVR is there but not hooked up to anything. I also found that the vac line coming out of the manifold wasn't even there. so I need to get some vacuum line to get that squared away. I also found a small black vac line in that generthat runs into the firewall that I'm guessing is for the ventilation controls? If thats the case can I just 'T' the line coming off the manifold, hook up the line going in to the firewall and continue to the EVR?

Click to expand...

Yes. That should work fine.

The diagram shows the vacuum fittings exactly as they are on the EGR vacuum regulator. The bottom port (or end) is connected to manifold vacuum and the top (or middle) port connects to the EGR valve.