Catalytic Converter(s) Question

[Dan Acosta]

I have a 2500 Yukon. The exhaust is quite a bit different than 1500 models and appears to be different than 2500 pick-ups. The cats are positioned at different lengths from the engine by about 20" In any case, I have been questioning my fuel mileage recently and thought to check the temperatures of the catalytic converters to determine if perhaps they are clogged or restrictive. After a a 30 minute drive, I immediately shot my IR temp sensor before and after the cat at each unit. On one pipe, the temp was higher before the cat, and the other the temp was hotter after the cat. It doesnt seem right, truck has 165k miles with a 6.0. It drives great, just kinda crappy mileage. Any thoughts?

 

[bottomline2000]

I have a 2500 Yukon. The exhaust is quite a bit different than 1500 models and appears to be different than 2500 pick-ups. The cats are positioned at different lengths from the engine by about 20" In any case, I have been questioning my fuel mileage recently and thought to check the temperatures of the catalytic converters to determine if perhaps they are clogged or restrictive. After a a 30 minute drive, I immediately shot my IR temp sensor before and after the cat at each unit. On one pipe, the temp was higher before the cat, and the other the temp was hotter after the cat. It doesnt seem right, truck has 165k miles with a 6.0. It drives great, just kinda crappy mileage. Any thoughts?

I've been doing the same test with my cats. Based on your findings I would say the cat with the higher temp up front is clogging or not as efficient as it should be. Both of mine are showing higher temps up front so somethimg is not right and i think a bad fuel pressure regulator may have caused the problem since it was dumpimg fuel into the intake..I'm going to do a vacuum test on mine as well to confirm what I think is true, both cats are losing or lost their efficiency..

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[swathdiver]

I have a 2500 Yukon. The exhaust is quite a bit different than 1500 models and appears to be different than 2500 pick-ups. The cats are positioned at different lengths from the engine by about 20" In any case, I have been questioning my fuel mileage recently and thought to check the temperatures of the catalytic converters to determine if perhaps they are clogged or restrictive. After a a 30 minute drive, I immediately shot my IR temp sensor before and after the cat at each unit. On one pipe, the temp was higher before the cat, and the other the temp was hotter after the cat. It doesnt seem right, truck has 165k miles with a 6.0. It drives great, just kinda crappy mileage. Any thoughts?

What's the mileage been?

A more precise way of examining them is with a Tech2 or bi-directional scan tool. You can see the temps of the cats and also run a graph of the O2 sensors, downstream and upstream, to check their condition and that of the cats as well.

 

[Dan Acosta]

What's the mileage been?

A more precise way of examining them is with a Tech2 or bi-directional scan tool. You can see the temps of the cats and also run a graph of the O2 sensors, downstream and upstream, to check their condition and that of the cats as well.

I am getting very lows 10s in the city. I asked a group of 2500 6.0 Yuks and Burbs and they were getting mid 11s. I would have opted for the 8.1 had I known the mpgs with this truck were not that far off. I dont know of a shop with those tools. I dont really want to take it to the stealership.

 

[swathdiver]

I am getting very lows 10s in the city. I asked a group of 2500 6.0 Yuks and Burbs and they were getting mid 11s. I would have opted for the 8.1 had I known the mpgs with this truck were not that far off. I dont know of a shop with those tools. I dont really want to take it to the stealership.

That's what I get on E85! You can buy your own Tech2 nowadays for $300-$400. When my cats were going bad, the mileage dropped about the same but got worse as time went on. Still drove great and we even raced it at the track a few months before replacing them.

 

[bottomline2000]

That's what I get on E85! You can buy your own Tech2 nowadays for $300-$400. When my cats were going bad, the mileage dropped about the same but got worse as time went on. Still drove great and we even raced it at the track a few months before replacing them.

a vacuum gauge is the original tech2.. it can tell you a lot for $20. I plugged mine up where the pcv tube connects to the intake and found I actually may have a restriction on my intake side! but none of my testing showed a clogged exhaust..its not dropping vacuum off idle at 3k rpm. I have high flow cats and they just seem to need more exhaust to heat up..

 

[bottomline2000]

That's what I get on E85! You can buy your own Tech2 nowadays for $300-$400. When my cats were going bad, the mileage dropped about the same but got worse as time went on. Still drove great and we even raced it at the track a few months before replacing them.

a vacuum gauge is the original tech2.. it can tell you a lot for $20. I plugged mine up where the pcv tube connects to the intake and found I actually may have a restriction on my intake side! but none of my testing showed a clogged exhaust..its not dropping vacuum off idle at 3k rpm. I have high flow cats and they just seem to need more exhaust to heat up..

 

[adriver]

Not too sure why the exhaust being different matters, (unless maybe you were going to find a used one to replace it with), but just to clarify; The 6.0 has a different exhaust then the 4.8/5.3. Your 2500 with the 6.0 MIGHT be the same exhaust as the Denali that came with the 6.0 standard. Otherwise the Escalade had the 6.0 optional from 2002-2004, and standard in 05 and 06. Whether or not its the same exhaust, I have no clue.

 

[Dan Acosta]

Not too sure why the exhaust being different matters, (unless maybe you were going to find a used one to replace it with), but just to clarify; The 6.0 has a different exhaust then the 4.8/5.3. Your 2500 with the 6.0 MIGHT be the same exhaust as the Denali that came with the 6.0 standard. Otherwise the Escalade had the 6.0 optional from 2002-2004, and standard in 05 and 06. Whether or not its the same exhaust, I have no clue.

It may not matter other than the positioning of the converters being different distances from the engine. Like I said it is about 20" difference. I guess I was wondering if the distance may effect temperatures and if someone had experience with this system. The 2500 Yukons & Burbs do have a different exhaust. I believe it is the same exhaust as the 8.1 2500 Yukons & Burbs. I could be wrong, but I havent been able to locate replacement exhaust components or too many aftermarket options.

 

[bottomline2000]

It may not matter other than the positioning of the converters being different distances from the engine. Like I said it is about 20" difference. I guess I was wondering if the distance may effect temperatures and if someone had experience with this system. The 2500 Yukons & Burbs do have a different exhaust. I believe it is the same exhaust as the 8.1 2500 Yukons & Burbs. I could be wrong, but I havent been able to locate replacement exhaust components or too many aftermarket options. View attachment 211425

You sure those aren't resonators. They are design to reduce exhaust drone in the cabin. That's pretty far back for catalytic converters. Stock cats are pretty close to the exhaust manifolds. One reason people turn off the rear 02 sensors with longtube headers is it moves the cats further back and they don't heat up as much and throw error codes..

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