Cat AFTER muffler?

[Manimal]

I thought the catalytic converter needed to be HOT to do it's job correctly? Why is there a cat AFTER the muffler on my 94 GMC Suburban 2500 7.4? I just BARELY passed Cali emissions test by the skin of my teeth. When I looked under it, I saw where the cat is! I just bought this thing 3 days ago.

 

[Texvet]

Guess - Someone jammed the cat on after the muffler, solely for the emissions testing?

 

[kennythewelder]

Most likely an OE Cali truck, and the rear cat is so it can pass emissions ,but that is just an educated guess. There are things on OE Cali trucks that no other trucks have on them. Same is true for cars.

 

[someotherguy]

Haven't seen a dead-stock original to compare to but it *might* be the way the truck came originally. Take a hard look at the pipe joints and see if it looks like there are any sketchy welds or joints that aren't smoothly cut, etc. anything that doesn't look OEM.

I can vouch for my 1995 3500HD 7.4 came factory with the big pancake cat after the muffler. Surprised me. It was a manual trans truck and only had the one wire (non-heated) O2 sensor, too, instead of the three wire heated sensor you would see on light duty auto trans C/K trucks starting in 1994.

Not the best pic but the cab is to the left. Bears mentioning it passed TX emissions like it was nothing and the truck had 200K on it. Cali emissions are the strictest in the nation so it doesn't surprise me your truck barely passed. Next time you may need to make some tweaks.

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Richard

 

[Supercharged111]

Ain't that some ****. Early 4.6 Ford Mustangs used 6 cats in their stock h pipes, 3 per side. Most others used 4, even OBDI.

 

[Big D]

My 91 has the Cat after the muffler as well, it was a head scratcher at the muffler shop.

 

[kennythewelder]

My 91 has the Cat after the muffler as well, it was a head scratcher at the muffler shop.

Must be a Cali thing I guess.

 

[Black_cirrus]

My 95 7.4 burb is also a post muffler cat some parts look ups even ask for placement, I think its either to tame flow so they don't blow out the cat guts (remember the factory had to warranty these things even if they spend all day at full throttle for years) or cats need oxygen to work and the muffler acts as a buffer to the cat. I'm guessing there is decent gas mileage gains to be had if tuned for a "normal" converter placement, or better yet tune for the engine and not emissions....

 

[Manimal]

I know this is a few months old, but would there be any adverse affects if I relocate the cat closer to the manifolds? As far as I can tell, the cats only have 1 part #.

 

[jasons99hoe]

if its OEM leave it alone. just replace as necessary. im so glad i dont live in california. (no offense its just waaaay different here). headers and no cats on anything i drive