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Old 12-15-2005, 04:10 PM
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Sufficient EGR vacuum signal?

Simple question. Jeep 4.0. How much vacuum should the egr valve receive to run fully open? My setup has this funky flying saucer shaped back pressure transducer (BPT) in the vacuum line that modulates vacuum according to a tube tapped into the exhaust. A lot of older Chrysler's have them too. Since I put a header on, (I hope) the back pressure's been reduced. On road test, with the guage installed in line before the bpt, the vacuum is 16-18hg. After the transducer, but before the valve, the vacuum is about 4hg. Is this enough?
The reason I ask is that I keep failing NOx treadmill test with a 3.43ppm when the limit is 3.0ppm. The HC and CO numbers are great, very low. If I apply vacuum to the valve at idle, the motor stalls, so I know the passages are open and the valve works. I'm just thinking there's not enough vacuum to open the valve all the way during the test.
I appreciate your input.
Thanks in advance.

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Old 12-17-2005, 03:24 PM
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Got it cornered, but need specialized vacuum valve.

Ok, a few minutes work with the vacuum guage and I have my answer. Not only is there no backpressure at the port, the header scavenges well enough to create a vacuum above 1500 rpm!
So, in order to preserve low rpm driveability, I need a normally closed vacuum valve that will open around 2"hg. Does anyone know if such a thing exists?
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