Stock 5.0 Egr/ecm Issues

[Sparky19]

I have a 93 GT 5.0 with AT, Engine is fresh and all vac hoses are new (No leaks) Good fuel pressure and injectors flow tested within spec. Have tested all connections to the sensors and Relays & solonoids. including the salt & pepper shakers. Removed as many connections as possible on the car cleaned the terminals and spread terminals for tight fit and coated with Silicon grease, I Have a breakout box & Factory repair manual & oscilloscope and have follwed through on most of the Pimpoint tests relating to general engine operation and the emmisions system Have tested every pin on breakout box and ALL operational pins do show activity within the paramiters of the rotunda cheat sheet. ECM diagnostic testing with engine on and off & going through all the bells & whistles produces no faulty codes only the typical system OK code.
All pipes and hoses are clear of carbon and check valves in great shape, Smog pump & TAB/TAD solonoids are new. The EGR valve & sensor & solonoid is new (Though the resistance of the return spring seems a little weaker than the original EGR). Every part of the engine & accesories has been maticulusly cleaned and specd or replaced. The EMC A9 "Remanufactured and all data stripped from the housing except rebuilder code wich googling returns nothing ) has been dissasembled and all tracing is excellent and no components show signs of overheating and all solder connections are bright & show n osigns of cracks or dulling or loose connections.
So here is the problem i am encountering:
At 750 to 1000 Rpm engine operates fairly well but when the RPM is increased to 1,200 Rpm & up to 1,900 rpm give or take a couple 100 rpm, the EGR valve starts to pulsate with lengthy shaft strokes & also the carbon canister vent to vacum valve starts to click about every 2 seconds as well. When dropped back to idle or above 2,000 Rpm the engine runs smooth and EGR valve And vapor vent valve relax to a closed state. When driving at low speed 30 mph and let off the gas or slightly adjust the fuel pedal to a lower state the car handles as if the rear brake drum is draging then freeing up it took a while for me to get away from the rear axle and focus on the engine itself and this is when i discovered that the EGR cycling is the drag release effect behing the wheel.
I am stumped by this activity i have googled this issue and came out empty handed, mostly just folks talking about idling issues. If someone with some experiance with this issue could help i would be most appreciative.

 

[jrichker]

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix.

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 125,000 hits, which indicates it does help fix idle problems quickly and inexpensively.

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

EGR System theory and testing

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. It does this by reducing the amount of air/fuel mixture that gets burned in the combustion process. This reduces combustion temperature, and the creation of NOx gases. The reduced combustion temp reduces the tendency to ping.

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.

The EVR regulates vacuum to the EGR valve to maintain the correct amount of vacuum. The solenoid coil should measure 20-70 Ohms resistance. The regulator has a vacuum feed on the bottom which draws from the intake manifold. The other vacuum line is regulated vacuum going to the EGR valve. One side of the EVR electrical circuit is +12 volts anytime the ignition switch is in the run position. The other side of the electrical circuit is the ground path and is controlled by the computer. The computer switches the ground on and off to control the regulator solenoid.


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 or see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.

Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).

Apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

If the engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.

If the engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.

If the engine stumbled, connect EGR test jig to the hose coming off of the EGR Valve.
Use your finger to cap the open port on the vacuum tee.
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 the EVR has failed

EGR test jig

To test the computer and wiring to the computer, you can use a test light across the EVR wiring connectors and dump the codes. When you dump the codes, the computer does a self test that toggles every relay/actuator/solenoid on and off. When this happens, the test light will flicker. If the test light remains on the computer or the wiring is suspect.

To check the EVR to computer wiring, disconnect the EVR connector and connect one end of the Ohmmeter to the dark green wire EVR wiring. Remove the passenger side kick panel and use a 10 MM socket to remove the computer connector from the computer. Set the Ohmmeter to high range and connect the other ohmmeter lead to ground. You should see an infinite open circuit indication or a reading greater than 1 Meg Ohm. If you see less than 200 Ohms, the dark green wire has shorted to ground somewhere.

Late Model Restoration may still have 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

 

[madspeed]

what he said