Smelly exhaust fumes

You should smell nothing from your 2001 exhaust! Have your independent mechanic rip out that useless Mercedes cat and order the correct OEM parts to replace the exhaust system front-to-back, and enjoy your Classic the way it was meant to perform. This should cost you in the neighborhood of 2 grand plus. I did this on my 2002 and the car purrs like a kitten---and no odor!

 

Welcome to the Gen1 forum... for your cat, I strongly recommend replacing whatever you have with an exact-fit aftermarket, such as the Eastern Catalytic #40544 (about $250 at RockAuto). A "universal cat" requires all kinds of extra work to get the O2 sensor mounted and then the whole thing fitted back to the exhaust manifold of the engine. The "exact fit" model, yes it's more expensive, but it will save TONS of time and frustration.

You may also need a fresh exhaust manifold to cat converter gasket (FelPro 61357, about $5 at RockAuto). If you find that you need to replace this gasket, you may find that fitting it up into the flange for the exhaust manifold a frustrating task; it's a TIGHT fit.

The best way to do the job is to drop the entire exhaust system (unplug #2 O2 sensor [under passenger side carpet], disconnect vacuum line to HCAC, 2 14mm head bolts connecting to muffler, 2 14mm head bolts connect cat converter to exhaust manifold, then disconnect 2 rubber support mounts in the middle). An O2 sensor socket attachment may be useful to get the O2 sensor off the old cat and onto the new one, or just buy a new O2 sensor - about $30 at RockAuto; get the Denso). You MIGHT find that the pipe that connects the cat converter to the HCAC assembly is pretty grotty, have holes or cracks that are hard to see, and contribute to noise when the engine is running and leak exhaust fumes into the passenger compartment. To inspect, remove the 3 bolts that hold the shield over the actuator of the HCAC pneumatic actuator {these may be rotted, so be prepared to dremel them off and replace with new 6mm nuts) and then dremel off the lower shield (welded in 4 spots to the exhaust pipe) and inspect the pipe. Patch any holes or cracks with Permatex Muffler compound or JB Weld, then clean up the pipe and cover it with a Permatex #80331 Muffler bandage. Bolt the actuator cover back in place and secure the lower shield with a (i think 6 inch diameter) stainless steel hose clamp.

While you have the midsection of the exhaust system down, you may want to paint it with high temp paint so that any cracks or holes are easier to find against a painted surface, not the rusty one. Drop the muffler (two rubber support hangers) and give that pipe and muffler a good examination, and patch any holes. The gasket that connects the intermediate pipe to the muffler is FelPro 61358 (about $5 at RockAuto). You may also find that the welded flanges that connect the intermediate pipe to the muffler are broken; you can fit a piece of 1 1/2 inch OD exhaust pipe into both halves to rejoin the sections, with liberal use of muffler putty and a couple of screws to hold stuff in place as a substitute for the double flange and gasket of the OEM design.

Once you're happy with the integrity of the exhaust system, bolt it back into place. I find a battery-operated drill with a 12" extension and 14mm deep socket make getting the front bolts (spring loaded) back into place a fairly easy job. Loading the springs and turning a ratchet by hand can also do the job, but be prepared for lots of failures as I find it difficult to get both pressure on the spring plus adequate rotation of the bolt to engage the threads all at the same time. Particularly if you're laying on your back under the car, in the driveway.

This is a good project for a dry autumn day, lots of patience for dealing with rusty and/or frozen bolts (Liquid Wrench is your friend here), and when you're done you can be assured that the exhaust gasses are being passed correctly to the muffler and out the exhaust pipe.

 

Also: pull the MultiFunction Display (the green vacuum-fluorescent thing that displays your miles, etc) and see if someone covered over the CheckEngine light. I find it hard to believe that whomever did the exhaust job before, did it well enough to make the Prius emissions control system happy. You might need a new O2 sensor, too, depending on what exactly was stolen (and then restored in the repair).

Let us know how you fare...