Hi merlin2021--thanks for replying.
The tube that looks coming out of the modulator does not supply exhaust to the EGR. To the contrary, exhaust gas goes out (it doesn t actually flow) from the EGR to the modulator through this tube.
There is no flex tube to supply exhaust. The EGR is bolted onto the intake manifold. Its bottom has two airway openings. Exhaust gas enters the lower opening into a pressure chamber inside the EGR base, then passes around the EGR valve when it opens, and goes out of the upper opening into the intake manifold. Unlike Ford cars that use a flex tube to get exhaust from the exhaust manifold (as you said), there is no flex tube here. Exhaust comes from a path that is built-in inside the intake manifold, but I have no idea where it comes beyond that.
The pressure chamber inside the EGR valve base has an opening that lets exhaust gas, through this tube, to pressure on a diaphragm inside the modulator. The modulator s P port gets vacuum when the throttle is opened but not too wide. Inside the modulator, P is connected to the atmosphere and vacuum is destroyed and can t reach Q (the output port) if this connection is not shut off. With sufficient exhaust pressure, the diaphragm will shut off the atmosphere connection to P so that vacuum will reach the EGR valve to open it. Port R gets vacuum when the throttle opens wider. R is not connected to the atmosphere and vacuum always passes to Q.
Toyota did not explain this in its materials, so I think it s worth sharing.
Now back to my own question. Right before I was to replace the modulator (as suggested by Toyota s materials), I found out there was no exhaust pressure at the tube, then found out exhaust never reached the EGR. There is a leak for sure, but it might be a combination of clog and leak. However, I have not done any big repairs and have no idea about the structure, components and weakness of this EGR exhaust path. I hope to have some guidance before I start (or decide to give up). Ideally, the question is best answered by someone who have worked on this model and have paid attention to the EGR exhaust source path that possibly involve the intake manifold, the engine head and the exhaust manifold. Any suggestion about what might be wrong inside these three parts will be helpful. You may or may not be very familiar with such a specific area, but I wonder whether it s OK with you to let or to ask other moderators to jump in?
Sunday, September 16th, 2007 AT 3:38 PM