Exhaust or catalyst issue?

[npschuma]

Hello all

So I took the new 1997 T4R out for a drive yesterday and going up hill with high throttle it seemed really under powered and then I noticed a strong smell almost like someone lit off fireworks under the car kind of a sulphur smell - pulled over and smell went away at idle

Looking under the truck, I see no clear disconnections in the exhaust system but interestingly, there is no flow coming out of the exhaust pipe can put your hand over it and feel nothing but can smell an exhaust smell in cab and at front of truck, no clear exhaust leak noises

No MIL on, no DTCs on scan tool but catalyst (and evap) drive cycles incomplete (O2 sensor and O2 sensor heater completed) - not sure what it takes to complete a catalyst or evap drive cycle

Running graph on O2 sensors (below) bank 1 sensor 1 seems to be cycling OK, bank 1 sensor 2, however, seems low voltage and is also cycling not pegged out at a specific voltage but not sure what could cause that

Wondering if the catalytic converter may be bad or if there is a blockage in the exhaust system somewhere....

Any thoughts?

Thanks as always for your help

 

[npschuma]

Sorry - the graph was captured with engine warm and running at about 2,500 RPM

 

[19963.4lsr5]

Is your tail pipe broken off at the rear of the muffler?


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[dogtail]

just maybe

 

[thegipper]

Sounds like your CAT is plugged up.

 

[npschuma]

So I think it is both. Finally crawled my fat self under the truck and yes, the exhaust is broken off at the muffler but with that smell on acceleration and the poor power + the O2 sensor waveforms I am thinking my cat is bad as well. I plan on just replacing the whole exhaust as its rusted out in a couple spots anyways. Glad I don't live in CA or NY

 

[TheDurk]

So I think it is both. Finally crawled my fat self under the truck and yes, the exhaust is broken off at the muffler but with that smell on acceleration and the poor power + the O2 sensor waveforms I am thinking my cat is bad as well. I plan on just replacing the whole exhaust as its rusted out in a couple spots anyways. Glad I don't live in CA or NY

On a '97, exhaust is the same for all 50 states. The only advantage is you don't need CARB approved parts, but NY does not require those or anybody else.

 

[19963.4lsr5]

I would just replace the muffler and tail pipe and O2 sensors. If that doesn’t solve your problem then replace the CAT. Aftermarket CATs do not last like an OEM one.

When you remove the muffler from the CAT and look in the back of it. As long as the honeycomb isn’t cracked or melted I’d leave it installed.

Exhaust leaks near O2 sensors will mess with the operation of the engine due to reversion.

The rear O2 sensor waveform should never look like the front waveform. It (rear sensor) needs to be lower amplitude and out of phase with the front sensor or it will trigger a P0420 code.


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[gamefreakgc]

I've spent a bit of time tracking the rear O2. Sometimes the signal will go flat, and sometimes it gives a waveform. Normally under acceleration or deceleration it will go flat and under cruise it will oscillate, but not in the same 0.0V - 0.9V range like the front.