exhaust question - PeachParts Mercedes-Benz Forum

amosfella · #1 08-05-2010, 04:20 AM

I was wondering if as the cat converters on exhaust systems get clogged, do they increase the temp of the operating system on the car?? I replaced the rad, cap, tstat, water pump on my car, all within the last 2 years, and yet, even on a cool day, the car gets to the 110 mark in stop and go traffic...
If the car is driving on the freeway, as the fuel consumption meter increases the fuel intake, the water temp correspondingly goes up within about a minute... As the consumption goes down, so does the temp...
The only link I seem to make now is that maybe the cats are getting plugged. I drive the same road once a week, and there is a big hill. When I first got the car, I was able to go right up it without it shifting down, now the place where it shifts is getting lower, and lower down the hill...
Should I be looking at gutting the cats?? If so, what kind of wire should be used to weld them back shut?? Just regular steel mig welding wire?? Are the heat shields important, or can I just discard them??
Thanks in advance.

400Eric · #2 08-05-2010, 07:34 AM

Yes, one or more cats may be plugged or plugging.

Don't eliminate the cats unless you are sure you'll be able to get away with it. Don't just "gut" them either. It's been proven that some back pressure is created by allowing the exhaust gasses into an open chamber and then forcing them back into a pipe again. The best way to do it is to run a straight pipe through the cat after gutting it by breaking up all the contents into pieces small enough to exit out each end. A plus of doing it this way is that you only have welding beads at each end of the cat instead of on it which makes it less suspicious looking. Welds on each end just look like the welds you would normally have when the cat was welded in place. (We have visual inspections out here.) Since the cats won't be making heat anymore, you won't need the heat shields but I'd leave them in place for the same "maintaining a stock look" reasons.

I don't think the wire type is important. I have two different friends who use coat hanger wire when they do exhaust system work.

You didn't say which car this is but eliminating the cats may cause O2 sensor issues since the pre-cat cats are often upstream of that sensor. On 96 and later cars (and some older ones) that will cause the C.E.L. to come on. Many folks here have cars that are not in their sigs, myself included. I'm curious, which car is this?
Regards, Eric

amosfella · #3 08-05-2010, 10:22 AM

95 S320. Inspection is not an issue for me. We don't have exhaust testing here... So looks aren't important for me.
I meant mig wire for welding the exhaust back together. I have both regular wire for steel, and stainless available at home here....

280EZRider · #4 08-05-2010, 11:40 AM

Eric has given you some great advice. Since you don't have emissions checks, I would remove the cats and the air pump, if you have one. It would also improve performance if you were to remove the EGR, if you have one. I would not remove any heat shields. Even without all the emissions stuff, there is still sufficient heat to do possible damage to the undercoating, and if nothing else to give you unwanted heat on the floor.