Hummer Exhaust Systems

General Exhaust Info:

1996 Turbo Diesel HUMMER H1 exhaust system described by AM General as a "tandem mounted," basically meaning in that case a Cat. Converter was mounted in line (in tandem) with the Muffler.  Not to be confused with AMG's exhaust system for the 1996 Unleaded Fuel ONLY Gasoline power trucks where there is a "Split Catalytic System" utilizing 2 Converters PLUS 2 "tandem mounted" Mufflers under the L.H. Rear Wheelhousing. 

• 1991, 1992 & 1993 H1 N/A Diesel: 1 ceramic wrapped Muffler plus 3 Heat Shields
• 1994 H1 N/A Diesel (Canada ONLY): 1 Resonator plus 1 ceramic wrapped Muffler plus 3 Heat Shields
• 1994 & 1995 H1 N/A Diesel: 1 Cat. Converter plus 1 ceramic wrapped Muffler plus 3 Heat Shields
• 1995 H1 Gasser (Unleaded Fuel ONLY): 2 Cat. Converters plus 1 ceramic wrapped Muffler plus 3 Heat Shields
• 1996 H1 Gasser (Unleaded Fuel ONLY): 2 Cat. Converters plus 2 ceramic wrapped Mufflers plus 3 Heat Shields plus L.H. Rear Wheelhousing Heat Shielding
• 1996 & newer H1 N/A & Turbo Diesels: 1 Cat. Converter plus 1 ceramic wrapped Muffler plus 3 Heat Shields

Replace Your Cat ?

Below is the catalytic converter assembly from a 98. The picture in the right shows the cells on the inside of the unit. It's in good repair and not clogged up at all. According to GM's engine specs there never was a need for a cat on this diesel, but it is installed on all Hummer Diesels and is not supposed to be removed. If you live in a state where they inspect your truck I wouldn't remove it.

In a diesel engine, with our particular vintages (2004 excluded), the biggest worries will be NOx, Carbon Monoxide, Hydrocarbons, Organic Solids, and Sulfur Dioxide. There are two types of EPA [Federal] Regs. that apply to  the HUMMER (H1)..."Engine Exhaust Emissions" AND "Vehicle Noise  Emissions."
 
FWIW; All diesel powered HUMMER (H1s) since 1994 model year use a  palladium-oxidation type catalytic converter.  This HUMMER diesel converter differs somewhat from the Gasser's two cat. converters.  Its  primary function is to oxidize the organic elements of diesel exhaust gasses  BEFORE they get to the muffler and further down stream.  It is NOT intended  to oxidize hydrocarbons or carbon monoxide or reduce nitrous oxides as the  Gasser's two cat's do.  The diesel HUMMER's converter operates best at  normal engine exhaust temperatures.

This is the primary reason why Caterpillar redid the engine computer for the Optimizer 6500 in the 04's.  The other area you can do emissions correction is in the engine computer and how it burns what it's given.

Taking the cat off and replacing it will take you at least 2 to 3 hours if you are laying on your back on the floor of your garage. If you have rusted clamps add more time. You have a hanger that's up above the tcase that's not easy to get to. You also have to remove some of the heat sheilds to pull the cat down and out. I reinstalled the heat shields and kept the cat in case I ever want to put it back.

All you need is the 'off road test pipe' and 3 - 3" muffler clamps. The photo shows where the cat used to be and the heat shield which I choose to keep. I figure that any heat I can keep off the truck is a good thing.

Removing the cat did not result in any gain in performance. It did get rid of some weight and bulk under the truck. It also gets rid of a heat source under the truck.