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Originally Posted by Bruno_300TE
(2) EGR valve Not sure that is a valid test for it: Applied pressure to the valve via the vacuum connection. The valve lost pressure quickly, suggesting it may not feel the vacuum that is required to operate it. Do I need a new valve? |
If the EGR vacuum diaphagm won't hold vacuum - using a Mighty Vac or similar vacuum pump to test - it's defective and needs to be replaced. When the engine is operating a leaky diaphagm might not open the valve, which would increase NOx.
The EGR valve only opens during cruise or light acceleration conditions. It is closed at idle and WOT. In addition to testing the valve diaphragm's ability to hold vacuum, you should also connect a Mighty Vac to the diaphagm at idle, and pump it down to at least 15" Hg. This should open the valve and cause the engine to idle rough. If this does not happen, the valve is probably frozen and the needs to be replaced.
A third test is to ensure that the EGR control system is functional. Tee a vacuum gage into the EGR valve vacuum line with a long test line so you can mount the vacuum gage in the cabin. Drive the car. During light acceleration and cruising at 40 MPH or more, you should see a vacuum reading on the gage. If not, troubleshoot the EGR valve control system.
Duke