02-20-2010, 06:01 PM
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Registered User
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Join Date: May 2007
Location: Arizona
Posts: 760
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This may help you to understand the EGR. It's #7 in the link below.
Quote:
1994 E320 EGR Problem
From your description, it actually sounds like your egr valve is stuck in the open position. There is no "internal engine valve dealing with the EGR system". The only component of the egr system is the egr itself.
Here is how the system works.
There is a way to check if your EGR valve is not working due to a plugged up hot inlet pipe, or if the valve itself is sticking (sticking in the open position or sticking in the closed position.):
The ECU sends an electric signal to the switch-over valve which opens the EGR valve to engine vacum. The vacum pulls open the diaphragm on the EGR, allowing some of the exhaust gas to recirculate back to the intake manifold (thus the name, Exhaust Gas Recirculation). The purpose is to reducing emissions.
The ECU will not send this electric signal at idle or wide open throttle, or until the engine has warmed up. So, if you hand pull about 12" of vacum on the EGR at idle with a warm engine, you are creating a very lean condition (vacum leak) and the engine will attemp to stall and run very rough. This tells you not only that the EGR is opening, but also that the hot inlet pipe is not completely plugged up. If, when you pull vacum and nothing changes, then you know that either the valve is not opening up, or the hot inlet pipe is completely blocked.
Now, release the hand vacum and the EGR should snap shut. Engine should smooth out.
In your case, your car is idling rough when cold, and the problem cleared up when the engine warmed up. This describes an egr that is stuck open.
There is another possibility that the diaphragm in the EGR itself may leak and cause an internal leak. The test for this is to see if the hand vacum will hold the EGR open for a period. It is common on vacum leaks to not be as noticeable with a cold engine as the engine is running rich and that helps off-set the added intake of air caused by the leak.
Last, when you clear the check engine light, it takes the same fault to occur over a specific period of time for the check engine light to come on again. It may take a few days, or even a week, but it will come on again.
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Paul S.
2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.
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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles
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