Everything EGR...

[Brett Garret]

If one of you guys could layout everything there is to know about this unit I would be grateful. Reason why is us 3.4s have the WORST time with those due to emittions and overall tuning. For those who don't know (basically non Texan, Californian, emitions testing) they place our cars on the dyno and put microphone looking things in the tailpipe and run the car at different speeds picking up our gases. F you ODB-II guys and your simple inspection. [img]graemlins/rant.gif[/img] It would also be great to learn about cleaning it and check for a bad egr. Thanks [img]graemlins/wavey.gif[/img]

[Coriya71]

EGR System Description
Linear EGR Valve




Purpose
The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by decreasing combustion temperature.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel/air mixture diluted by the exhaust gases, combustion temperatures are reduced.

Operation


The linear EGR valve is designed to accurately supply EGR to an engine independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The feedback signal can be monitored with a scan tool as ACTUAL EGR POS. ACTUAL EGR POS should always be near the commanded EGR position ( DESIRED EGR POS). The PCM uses information from the following sensors to control the pintle position:

Engine Coolant Temperature (ECT) sensor.
Throttle Position (TP) sensor.
Mass Air Flow (MAF).
The linear EGR valve is usually activated under the following conditions:

Warm engine operation
Above idle speed
Diagnosis


Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:

Engine stalls after cold start.
Engine stalls during closed throttle conditions.
Vehicle surges during cruise.
Rough idle.
DTC P0300 (misfire detected).
Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:

Spark knock (detonation).
Engine overheating.
Emission test failure.
DTC P0401.
Poor fuel economy.
EGR flow diagnosis is included in the DTC P0401 diagnostic table. Pintle position error diagnosis is covered in DTC P1406. If EGR diagnostic trouble codes P0401 and/or P1406 are encountered, go to the DTC tables for diagnosis.

[HBHRacing]

ah the wonders of the liner EGR valve. Here is what I can tell you in a nut shell. Actual valve faults are rare. Most times it's a pintal postion error that will cause problems. As a part of emissions you need the valve to work at max. One thing that keeps this from happening is carbon biuldup in the EGR passage way. When this happens the EGR is commanded on, Because of the blockage the exhaust flow is week and will not cool combustion chambers enough. It takes almost compleate cloging of the passage to set an inseficiant flow code however it does happen. When the EGR valve runs a passive test it looks for desired valve position VS actual position. if this verys it will set a code. Another test is when the valve is comanded on the PCM looks for a Change in map voltage. If none or not enough it will set a flow code.

In order to effectivly clean the passage way upper intake removal is needed. By cleaning the pasage and intake really really well you can uusualy have no prblem passing the sniffer test.

Adressing the pintal position problem. Most faults ocure because the PCM will learn the incorrect closed postion. cleaning the EGR and making sure there is nothing holding the pintal open is the first step. Then replace the valve and make the PCM relearn closed position. This is not easy to do without the help of a tech 2 GM scanner but if you unhook the battery for several minutes. Then you can unhook the EGR valve conector, cycle the key, turn it back off and plug the valve in, cylce the key again and it should now read 0 for closed position..

[StudlyCamaro]

Originally posted by Brett Garret:
If one of you guys could layout everything there is to know about this unit I would be grateful. Reason why is us 3.4s have the WORST time with those due to emittions and overall tuning.

i dont follow your thinking here... your car should produce less emissions with the egr, not more... and how does an EGR valve screw with tuning?

im lost

[Brett Garret]

I've failed emissions because my EGR was dirty/old. If it doesn't work right our NOX levels will be very high. When I said tuning I actually ment with it (the EGR). I should've worded it better.