egr valve

[meathead40]

my muffler is split right down the seam and blown out. would this reduce the back pressure enough to cause the egr valve to not work properly even though the valve is at the manifold?

[PaulJ]

Shouldn't matter, do you have driveability symptoms?

[Matthew Currie]

I suspect it shouldn't matter if the cat is still on, but it may also depend on which kind of EGR valve you have. The earlier ones, such as on the 87, had a back-pressure valve in the diaphragm. Later ones (which should include the 90) do not, and I don't think it should matter. If you have a vacuum pump, and the diaphragm holds vacuum with the engine off, you have no back-pressure valve (and a good diaphragm). It's easy to figure when the valve sticks open (no idle), but I don't know an easy way of determining if it fails to open when it should, because one of the usual ways (increased knock) is cancelled out on an XJ by the knock sensor.