Quote:
Originally Posted by Christ
It's a thought... I'm not totally sure about it.
I don't really think that adding EGR is going to reduce the vacuum, because it's just adding mass from an area other than the throttle body. In other words, the engine is still drawing the same vacuum on the manifold, but the EGR is basically a second intake source. While you would show less flow through the throttle body, the vacuum figure should be the same regardless of EGR flow. (Some fluctuation might be noted due to expansion of heated gasses, etc.. )
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I'd expect a reduction in vacuum with EGR. Since EGR reduces power, you'll have to open the throttle further to maintain the same speed. And the EGR flow you're letting into the intake manifold is higher pressure than the ambient pressure entering the throttle body, so that alone should decrease vacuum even if throttle position remains the same.
Also, the ECU in Suzukis (as well as other cars) uses the MAP sensor to monitor EGR function. If the ECU doesn't see the expected change in MAP when the EGR valve is told to open, you get a CEL. But from what I've read, it's a very small change in vacuum. But if you're increasing EGR flow, that could change.