ASE Online Training: EGR
This EGR page is for the students who are in my Level 1 Smog license and Repair license Class, hopefully, the information here will assist you in passing the final exam.
Conventional Exhaust Gas Recirculation “EGR” Valve:
A standard or conventional valve is basically a valve which helps reduce Nox.
This was one of the first valves develop to help reduce Nox emissions.
For an EGR valve to work properly, three conditions must be satisfied.
1.) Vacuum”ported vacuum” or the correct signal to the EGR Solenoid from the PCM must be supplied to the valve at the right time.
2.) The valve stem must move freely to allow inert gases to flow through the EGR passage to the combustion chamber.
3.) All passages must be cleared and free of obstruction to allow the inert gasses to flow.
Let’s talk about how the valve works, it receives ported vacuum from a thermal vacuum switch or solenoid, the EGR valve Diaphragm then moves up and injects inert gas from the exhaust into the intake system which flows through the intake to the combustion chamber.
This inert gas will then lower the combustion chamber temperature; because it displaces the normal oxygen content level and in turn will lower the combustion chamber temperature below 2500f.
Remember any thing that will raise the temperature in the combustion chamber above 2500f can create Nox.
ASE Online Training: EGR – Conventional EGR:
Testing this valve is very simple: you disconnect the vacuum line from the valve and attach a hand vacuum pump to the valve. The technician applies 10 – 15 in of vacuum to the valve.
The engine should begin to idle rough or stall on a conventional system, on positive backpressure systems there will be no response.
This will indicate two things, the valve works and the intake manifold port is not plugged.
If there is no response the valve has to be remove and inspected, either you have a defective valve or plugged intake manifold which in either case will increase Nox
Don’t forget the vacuum signal, every valve most receive some type of signal to operate the valve on a normal operating temperature engine.
The hose you just remove from the valve, attach a vacuum gauge to that hose, now while the car is in park or neutral rev the engine to 1,000 -1,500 RPM’S and observe the gauge, you should see anywhere between 3′ – 7″ of vacuum on some vehicles.
If there is no vacuum reading find a troubleshooting chart for that manufacturer and follow the troubleshooting procedure for non-operational EGR system.
BACK PRESSURE EXHAUST GAS RECIRCULATION VALVE:
Now let’s talk about the back pressure EGR valve it basically works the same as the conventional valve, but it needs back pressure from the exhaust to operate.
If the valve does not receive back pressure the valve will not move.
Internally there is a vent that is in the open position, with the correct back pressure the internal diaphragm will close the vent, now when the vacuum is being applied with the vent close it will not bleed off.
The diaphragm will now lift the pintle off it’s seat so the port will open.
This allows the inert gas from the exhaust to flow from exhaust through the intake manifold to the combustion chamber which will lower the temperature and again this will lower Nox emissions.
ASE Online Training: EGR – THE BACK PRESSURE EGR VALVE:
However testing this valve is a little different from the conventional valve. When you disconnect the vacuum line from the back pressure valve and attach a hand vacuum pump to the EGR valve.
The engine should not stall when vacuum is applied to the valve, because the vacuum will bleed off, because there is no back pressure and the vent is open.
Once you apply back pressure to the exhaust then apply vacuum to the valve, (use a hand vacuum pump) it should cause the engine to run roughly or stall because the vent will close and the vacuum will not bleed off.
Again this indicates the valve is working and the ports are cleared; remember to confirm you have a vacuum signal to the valve also.
The hose you just remove from the valve attach a vacuum gauge to that hose, now while the car is in park or neutral rev the engine to 1,000 -1,500 RPM’S observe the gauge you should see anywhere between 3′ – 7″ of vacuum. Note on some vehicles the computer may need to see a vehicle speed signal before applying a signal to the EGR Solenoid to trigger vacuum to the EGR Solenoid.
If there is no vacuum reading find a troubleshooting chart for that manufacturer and follow the troubleshooting procedure for no vacuum signal to the valve.
Always follow the manufacturer procedure any time you are troubleshooting.
ASE Online Training
EGR – Pressure Exhaust Gas Recirculation Valve:
A negative pressure exhaust gas recirculation valve is similar to a positive valve, but if you apply vacuum to the positive valve at idle there will be no reaction do to the open internal vent.
If you apply vacuum to a negative exhaust gas recirculation valve and watch the diaphragm with a mirror the diaphragm should move freely and hold vacuum for at least 20 seconds.
This question is for the students in my class; let’s see how well you have been paying attention:
Testing the positive backpressure EGR valve you get the vehicle at normal operating temperature and running at idle. You open the EGR valve by pushing up on under-side of the EGR valve diaphragm.
The Idle speed should drop at this time If idle does not drop this indicates what about the system?
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EGR – vehicles do not have EGR’s:
Some vehicles do not have EGR valves to control Nox emissions, so how is the Nox control?
Well there are a few ways:
Combustion Chamber Design
Exhaust and Intake valve positioning
Increase camshaft overlap
ASE Online Training: EGR
The main purpose of the EGR is to reduce Nox, Oxides of Nitrogen
When testing a Positive Backpressure EGR Valve, applying vacuum to the diagram alone will not affect the idle speed. In order for the EGR Valve to function back pressure must be applied also.
Here is a question for my readers?
While performing a functional check on the EGR system, you push up on the EGR valve and the vehicle stalls, you then install a vacuum gauge in the EGR vacuum line to check and confirm vacuum. The gauge reads 5 – 7 inches of vacuum on slight acceleration. Now with the information you have is this a complete assessment of the EGR circuit?
No, it is not, this is an incomplete test, there was never a functional check perform on the actual EGR.