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  #1  
Old 02-07-2009, 01:30 PM
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Location: Reno, NV
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Clogged Pre Catalytic converter..the fix

OK, time to pay back all the good info you guys have provided.
Owning an MB would be a real hassle without being able to
find the answers to my maintenance questions here.

Here's the story: saw an add in my local craigslist for a 1989 300E, for 500 bucks...how good could it be? No pic of course. Ad said it had vacuum leak issues. But what the heck, it was nearby, so I went to look.
Beautiful car, 219,000 miles, perfect interior except some cracking of the
wood console. In the trunk, a complete intake assembly from throttle body to fuel distributor, two new headlights, new belts, lots of other stuff. Car has new brakes, rotors, master cylinder, 10 disc CD changer....yada yada.

On the test drive, fires right up, idles smooth, no smoke. Wont go over 3500 rpm. Otherwise drives wonderfully.
Sort of stutters like the ignition was cutting out, right at 3500. Everything else on the car functions perfectly, from the power antenna to the sunroof, windows, even the seats are perfect.
I haggle the guy down to $400 and buy it, since I'm fairly handy with a wrench, and if need be I could part it out on ebay for more than $400.

Every sensor had been replaced by the previous owner, along with Bosch plug wires, it had new H9DCO plugs. Pulled the air cleaner, and with the engine running I could hear a distinctive "crackle/pop" from the intake with the engine revved up. Vacuum gauge on the dash never goes near the left end of the scale, mostly stayed in the middle at idle, red area when revved, i.e. low vacuum.
Pulled the bolts from the header to tailpipe connection, and with a flashlight looked down at the surface of the pre-cats....completely plugged. Amazing that the car runs at all! Getting the tailpipe and main converter assembly off the car with only ramps and jacks is a REAL hassle, since it is about a third the length of the vehicle (I dug a trench in the ground under the car). I've attached photos of what plugged pre-cats look like, and my cure; cut an access hatch into the underside of the STAINLESS STEEL pipe, chop out the stainless honeycomb pre-cat material (tough!), and MIG weld the access closed. I also hollowed out the main converter, since it was probably clogged with whatever jammed the pre-cats.

The result? Car runs like a champ, gets 20.5 mpg in city driving at an adult pace, and passed Nevada smog without a problem, (although I cheat and use 50/50 mix of pure denatured alcohol/gasoline for the 10 minutes the test takes).
Vacuum gauge now stays pegged at the left, on the high vacuum side of the scale unless my foot is using some throttle. At a steady 35 on flat ground it is tight against the left end of the scale.

If you have pre-cats on an older MB, and if you have not looked at their surfaces lately, I urge you to do so, especially if you are down on power, have low gas mileage, and have low vacuum indications. That "crackle/pop" noise I heard was the exhaust valves opening and trying to vent through the easiest path...back out the intake!

Attached Thumbnails
Clogged Pre Catalytic converter..the fix-hpim0859.jpg   Clogged Pre Catalytic converter..the fix-hpim0860.jpg   Clogged Pre Catalytic converter..the fix-hpim0857.jpg   Clogged Pre Catalytic converter..the fix-hpim0840.jpg  
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Old 02-08-2009, 08:29 AM
Hirnbeiss's Avatar
ich fahre, also bin ich
 
Join Date: Mar 2002
Location: South Florida
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Wow, good work. I've always wanted to get back at the EPA like that. Did you get the idea form your day job as a cosmetic surgeon?
Any problems welding the stainless?
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Old 02-08-2009, 09:38 AM
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Location: Waterloo Illinois
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Does the car sound any different?
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Old 02-08-2009, 11:28 PM
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Join Date: Feb 2005
Location: Frederick, Md
Posts: 4,540
Wow amazing. Good Job!
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1980 500SE/AMG Euro
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1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
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past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350
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Old 02-10-2009, 07:24 AM
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Location: Reno, NV
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Re:pre-cats

No problem welding the stainless, I have lots of MIG time but this was my first stainless. I had to use mild steel argon/CO2 gas with stainless wire, since that was what was available; it worked, but the welds were ugly.
Preparation grinding is key to getting it welded shut, with beveled edges and CLEAN surfaces to weld upon.

The car was VERY quiet before when clogged, now it sounds just a tiny bit more throaty than stock, not loud at all. There's still a lot of muffler after that cat can.
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Old 03-14-2017, 07:57 PM
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Location: Blighty
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Spent a while trying to order a new exhaust but unable to source one with the two canisters as per photo below.



Are these units similar to the canisters shown by OP in post 1?

Thanks
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1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)
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Old 05-25-2018, 04:59 PM
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What's happened to photos, posts are missing ?

(not photobucket related)

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1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)
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