Hi all you gear heads,

I've heard that I can make a ton of performance improvements if I bypass my Catalytic converter on my 91 350 SD.

I'm going to do it if it's legal. I've got no problems walking in the gray areas if that's what I need to do.

I was told there is a bypass for it on line but they forgot what it was called. Anyone know what it's called?

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Diesel Dork

I make my own B100 with a Bio Pro 190 and run my deisels on it for $.97/gal

Have
1991 Mercedes 350 SD
1998 Dodge Ram 2500 Cummins
2005 Mercedes Sprinter
1956 Cadillac Coupe deVille
1996 Dodge Ram 2500 4x4 gas only to pick up WVO
Sold
1983 Mercedes 500 SEL gas

Any removal of any smog-control parts built in at the factory or added/replaced later to meet current smog requirements is probably illegal in California as in other states that have such laws in place for 1991-model diesels. OTOH, the risk of getting caught is low, since no inspection is required in California for 1997 and older cars. If whatever you do causes the tailpipe to start emitting great clouds of smoke, you could get stopped by any sworn officer and cited, possibly leading to an inspection uncovering the missing cat.

OTOH, it's possible that removal of the cat may not help your car. It depends on whether the cat is in good condition (not clogged) or badly clogged with soot due to too many years of granny-driving. Many people are sure they can help their car's performance by changing the exhaust system but usually all they get is more noise.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I'm pretty sure tampering with smog equipment is a violation of federal law, but I don't have the section of USC to cite at the moment. However, people do it all the time and hardly ever get caught.

This is also very true. I'd also be concerned about saving money for the replacement engine when that rod-bender lives up to its name.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.

You'll never get stopped by a cop in California if your car is admitting to much smoke.....I was followed along way when I first started driving my euro 300d that sat for ages.....there was such a huge cloud of smoke behind it....you could see it from space....my trunk lid didn't say diesel....the cop stayed behind me and ran my plates....then after awhile he just went around...

A citizen reported that same car in el cerrito for it smoking.....I just got a nice letter in the mail from some outfit related to California's clean air act....I tossed it....

Remove it if you want, but as was said....it may not fix anything.....not positive on this model but the egr valve can cause an intake to plug solid causing issues...

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No its not legal in CA or anywhere in the US but since CA doesn't smog pre 98 diesels, nobody will ever notice. You will only gain a slight bit of spool up time if your cat is clogged which is likely at this age. Don't expect anything dramatic.

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CENSORED due to not family friendly words

Yup it's illegal...just like

• Parking at an expired meter
• Washing your car on the driveway
• Driving at speeds in excess of the posted limit
• Driving with your check engine light on
• Not FULLY stopping at a stop sign
• Playing your stereo too loud
• Not having a white rear license light
• Driving without a bumper
• Driving without a rear reflector
• Loud exhaust
• Talking on a cell phone
• Not paying sales tax on those car parts you bought on the Internet
• Venting R134a from your A/C (legal if its in a computer duster can though)

And of course, lets not forget about some of the other stupid laws out there

In Alabama, it’s illegal for a driver to be blindfolded while operating a vehicle. However, it is legal to drive the wrong way on a one way street if you have a lantern on the front of your car.

In Denver, Colorado, it is illegal to drive a black car on Sunday.

In Coeur d’Alene, Idaho, it’s legal to make love while parked. Police officers aren’t allowed to walk up and knock on the window. Any suspicious officer who thinks that sex is taking place must drive up from behind, honk his horn three times and wait approximately two minutes before getting out of his car to investigate.

In Massachusetts, taxi drivers are prohibited from making love in the front seat of their taxi during their shifts.

In New Mexico, it’s legal for couples to have sex in a parked vehicle during their lunch break from work, as long as the car or van has drawn curtains to stop strangers from peeking.

In Ohio, riding on the roof of a taxi cab is not allowed. Also, the Ohio driver’s education manual states that you must honk the horn whenever you pass another car.

In Tennessee, a man must walk in front of any car driven by a woman while waving a red flag as a warning.

In Tremonton, Utah, no woman may have sex with a man while riding in an ambulance. If caught, the woman can be charged with a sexual misdemeanor and "her name is to be published in the local newspaper." The man isn’t charged nor is his name revealed.

In Washington, it is mandatory for a motorist with criminal intentions to stop at the city limits and telephone the Chief of Police as he is entering the town.


Read more: Ten Stupid Car Laws - Top Speed


Is it illegal...of course. But then so is almost everything. The real concern is can you handle the fine in the highly unlikely event you are highly unlucky.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

What catalytic converter?

W126 350 cars do not have one. The sticker on your radiator support should say "NON-CATALYST" on it.



If it did have one you would see few / no gains from removing it. Diesel oxidation cats don't rob that much power in near stock configs.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

It might be the Officer thought You had enough trouble and that Your Car was not going to last much longer

You can be cited for excessive Smoke on any Vehicle. I have no idea why you were not cited.

Back in 1972 I had a Car that had excessive Blow-by out of the Draft Tube that would collect under the Hood at idle. When you took off all that Smoke came out and left a nice cloud behind you. Once moving there was no visible smoke.

I was pulled over by the City Police and the Officer would not listen to the fact that I was Home on Leave from the Army and was going back I 3 Days so no one would be driving the Car.

The Officer had his Ticket Book out and was about to write and He got a Radio Call. He was clearly pissed off that He got the Call and had to go without writing the Ticket.

So I would say that for sure they can Ticket you for smoke.

Here in Long Beach they successfully banned Older Diesel Trucks from entering the Port.

About in 1993 I twice saw the set up Road Blocks in the City of Los Angeles randomly pulling Cars over and were checking to see if People had bypassed their Emission System on Cars and even doing Tail Pipe Tests.

I was waved by as I was driving the Volvo Diesel.

About one Year ago I think I saw them doing that again but was too far away to be sure what they were doing.

I don't know if they were ticketing People or not or if it was just a fact finding inspection.

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84 300D, 82 Volvo 244Gl Diesel

Where did you hear that? The limit of .97 mods is loosening the ALDA and full load stop. The OE exhaust system will easily handle that. You can do a 606 turbo swap but the 98-99 E300 exhaust system doesn't look to me to flow any better. A less restrictive exhaust system isn't beneficial until you run a $$$ MYNA pump.

Test pipe?

Sixto
87 300D

What is part 8 in this diagram? because that's where my catalytic converter is.

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Diesel Dork

I make my own B100 with a Bio Pro 190 and run my deisels on it for $.97/gal

Have
1991 Mercedes 350 SD
1998 Dodge Ram 2500 Cummins
2005 Mercedes Sprinter
1956 Cadillac Coupe deVille
1996 Dodge Ram 2500 4x4 gas only to pick up WVO
Sold
1983 Mercedes 500 SEL gas

Thanks

__________________
Diesel Dork

I make my own B100 with a Bio Pro 190 and run my deisels on it for $.97/gal

Have
1991 Mercedes 350 SD
1998 Dodge Ram 2500 Cummins
2005 Mercedes Sprinter
1956 Cadillac Coupe deVille
1996 Dodge Ram 2500 4x4 gas only to pick up WVO
Sold
1983 Mercedes 500 SEL gas

Part 8 is a muffler. A cat mounted that far back in the exhaust would do nothing.

-J

__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.