Go With the Flow
The EGR valve has been around since 1973 when
the first exhaust gas recirculating systems were
developed for production cars. Exhaust gas
recirculation system reduces the formation of
harmful NOX gases by allowing a small amount
of exhaust gas to be introduced into the intake
manifold. This small amount of exhaust gas only
makes up about 6 to 10% of the total incoming
air fuel mix, but it's enough to dilute the air/fuel
mixture to create a "cooling effect" on the
overall combustion temperatures. This is accomplished because the exhaust mixture has less oxygen in it than the incoming fresh air. By doing so, the combustion temperatures can stay below the range of 2800 degrees F, which effectively reduces the reaction between the nitrogen and oxygen that are present in the combustion chamber to form the NOx gases.
Other methods may be used to minimize NOx. These include increasing camshaft valve overlap, redesigning the combustion chamber and modifying ignition advance curves. Three-way catalytic converters also reduce NOx in the exhaust too. With Variable Valve Timing (VVT), there is no EGR valve because the VVT system varies the timing of the exhaust valves to provide the same effect as EGR. By changing the point at which the exhaust valves close when the engine is working hard under load, a small amount of exhaust gas can be retained in the cylinders for the next combustion cycle. This has the same effect on reducing combustion temperatures and NOx as an EGR valve. The big difference is that the VVT system can react to changing engine loads much more quickly and more precisely than a traditional EGR valve. Using VVT for EGR also eliminates many of the problems associated with EGR system failures.
Symptoms of a failed EGR system
Overtime, small carbon deposits accumulate along the intake manifold passages, connecting tubes, and the EGR valve itself. Eventually, all this carbon build up will affect the valve's plunger causing it to stick open or close as well as clogging the lines or intake manifold. To add to that, the EGR electrical contact points inside the potentiometer (on the electrical type) can wear out causing the EGR to no longer report back to the PCM of its actual position. Some of the most common problems associated with a failed EGR system are: 1.Rough idle 2.Fuel economy 3.Lack of power on acceleration 4.Service light on with codes such as P0401 (EGR insufficient flow) to P1406 (EGR pintle position – Ford) codes. It’s not uncommon to get a car in the shop with the EGR system disconnected or inoperable. IF the EGR system is rendered inoperative because it was disconnected or tampered with, the combustion cooling effect will be lost. Without EGR, the engine will often knock and ping (detonate) when accelerating or lugging the engine. This can cause engine damage over time and damage to the catalytic converter as well.
Different Types of EGR valves
Over the years the EGR valve has changed and evolved with the newer engine styles and emissions systems. The first types were simple in comparison to today’s EGR, but their function is basically the same. There are basically six different types of EGR systems in use.
Ported EGR valves (1973 to 1980s). The typical ported vacuum EGR valve consists of a vacuum diaphragm connected to a poppet or tapered stem flow control valve.
Positive backpressure EGR valves (1973 & up).
Backpressure EGR. Backpressure EGR valves use exhaust backpressure to vary the point at which they open and their flow rates.
Negative backpressure EGR valves (1973 & up). The negative backpressure type of EGR valve reacts in the same way as the positive feedback type, except that it reacts to a negative or decreasing pressure change in the exhaust system to regulate EGR action.
Pulse-width modulated electronic EGR valves (early 1980s & up). First used in 1984 by General Motors, this type of EGR system uses a pulse width-modulated EGR control solenoid.
Digital electronic EGR valves (late 1980s to 1990s). On some applications, a "digital" EGR valve is used. This type of valve also uses vacuum to open the valve but regulates EGR flow according to computer control.
Linear electronic EGR valves (early 1990s & up). Another type of electronic EGR valve is the "linear" EGR valve. This type uses a small computer-controlled stepper motor to open and close the EGR valve instead of vacuum.
Basic testing Vacuum type EGR
Connect a hand vacuum pump to the EGR valve in place of the vacuum hose and apply 15 in-Hg of vacuum to the valve. As you apply vacuum to the valve, check for diaphragm movement. Also, pay attention to engine idle. Idle should become rough or the engine should stall as you apply vacuum.
Electronic EGR testing
A scanner is the most widely used piece of equipment in testing the electrical type EGR. For one reason, the codes and the corresponding diagnostics, the other (when possible) a BIAS control to allow the technician to operate the EGR solenoid. If operating the solenoid is not possible, there is another way.
Almost all of the electronic EGR’s I’ve dealt with have 5 wires. The two outside wires are generally the solenoid 12 volt B+ and the other is the negative (control) lead from the PCM. If you are unsure of their locations consult the wiring diagram to confirm the locations.
Another way to determine the actual leads is to hook up your multimeter to one of the leads and of the outside leads. Turn the key on and look for the 12 volt feed signal. The negative side should be off from the PCM which means either wire (assuming the EGR solenoid is good) will show B+, but disconnecting the connector one will remain B+ while the other will not. The lead with no B+ will most likely be the PCM control wire. (Consult the wiring diagram to be sure).
With the leads sorted out, a quick check by grounding the PCM control wire will determine if the problem is with the EGR solenoid or not. Of course the actual potentiometer is still in question as to whether it is in working order. I prefer a scope for the next test.
Of the three remaining leads one is the reference voltage (generally 5 volts) one is a ground and one is back to the computer. Since most of the electronic solenoid driven EGR’s are pulse width modulated it’s not likely you’ll be able to hold the pintle at a given percentage (Unless you happen to have a bi-directional control in your scanner) so the best thing that I’ve found is to read the values as you apply the negative voltage to the EGR solenoid. A solid signal without a lot of chatter usually indicates a good EGR. A signal that doesn’t show a clean signal generally indicates worn contact points in the EGR potentiometer.
The DPFE (Differential Pressure Feedback EGR system) responds to the EGR flow in the intake manifold by reading the pressure differences. 1.Attach a vacuum pump to the EGR valve. 2.Connect your multimeter to the outside lead of the DPFE connector (B+ lead). (A wiring diagram will helpful) 3.Connect your negative lead to your multimeter to a known good ground. 4.Start the vehicle and look for a reading of around .9 volts. 5.Apply vacuum to the EGR. As the vacuum increases the idle should begin to get rough or even stall. There should be a voltage change at the DPFE as the vacuum is increased. 6.This will confirm if DPFE is at least reading and that the lines are OK.
Ford EGR Vacuum regulator solenoid
Test No#1 (Service bay test)
1. Locate the B+ lead and the computer ground control lead.
2. Start the engine and allow it to idle.
3. Test that the B+ lead does have voltage present.
4. Temporarily ground the computer signal lead. As you do the engine should stumble or even stall out as the vacuum regulator solenoid opens up and allows vacuum to be sent to the EGR.
This will confirm that vacuum is present, the solenoid is in working order, the EGR valve is functioning, and that the passage ways are reasonably free of debris.
Test No#2 (Drive test)
The engine needs to be up to operating temperature before continuing.
1.Disconnect the vacuum line or hose that is connected to the EGR valve. 2.Connect a piece of vacuum hose to the vacuum line long enough to reach out under the hood once it is closed. 3.Snake the vacuum hose out from under the hood and secure it under a wiper arm. 4.Connect your vacuum gauge to the end of the vacuum hose and secure it with the wiper arm. 5.Make sure the gauge can be easily seen as you go on your drive test. Find a safe route to drive test the vehicle with an observer watching the gauge. The vacuum gauge's needle should move up to 5 in.Hg only when you start to accelerate. After the needle moves up to 5 in.HG, the gauge should always drop down (immediately) to 0 (zero) in.HG when you come off the accelerator pedal.
Follow these steps and I’m sure the next time you’re testing an EGR system it will be far easier than before. The more you test the more you can confirm a problem without changing parts that didn’t need to be changed.