2004 Blazer runs normal cold start, plenty of power. Bogs down after warm up, diminishing power, won't go. Catalytic Converter? What is temp sensitive could bog engine down?

believe what you are describing is a plugged catalytic converter / exhaust. The converter could be plugging up when getting warm, then working again once it cools down. Check your exhaust when you start it cold and see if it becomes restricted after warming up. You can also read the temp. on the exhaust before the converter and after the converter to see if it's plugged.

Given the P0420 code it's possible it's a cat converter. But then the question is what caused the cat converter to go bad? They don't go bad on their own. You've most likely got multiple problems going on here. Get it diagnosed by a pro.

You need to perform an OBDII diagnostic test and look at the stored faults. Sounds like a temp sensor or Mass Airflow Sensor. Also dirty air filter needs to be changed every 40,000 miles. be sure to delete stored faults and recheck OBDII periodically for new faults.

By run - do you mean it dies when you put it in gear? Or that it just bogs down when you attempt to accelerate or drive away?
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A plugged Catalytic converter will cause this. So will a Bad MAP or MAS (Mas Air ) sensor. So will a bad TPS (Throttle Position) sensor.
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Need more input to answer more precisely.

First I'd confirm proper fuel pressure, then I'd look in to possible plugged catalytic converter. Any other symptoms such as sluggish up hill, worse when warmed up, poor fuel mileage?

Sounds like you have the famous cam position failure.Dont rely on a code it wont give you any By the way does the idle roll and surge ? Then its definately your cam postion sensor

If there's no power loss while accelerating, 99.9% guaranteed not to be the cat. converter. I'd start with the ignition module. When they go bad they can, almost always, still work properly when they're cold but then fail after they warm up, and it's because of this fact that when you have it tested, it needs to be tested 4-5 times in a row. This constant testing will bring it up to the temp where it would fail. Even a bad module will pass the first couple tests.

It could be a catalytic converter, fuel, or air intake issue. To test the cat. start the truck and let it reach normal operating temp. run in park or nutral at 2500 rpm for 3 min. after 3 min continue to run at 2500 rpm and measure the temprature at the front of the cat and at the rear of the cat. It should be at least 200 degrees hotter after the cat. If not replace it.

check fuel pressure and volume to make sure you are within specs.

Also on the back of the distributor is a ignition controll module that go out all the time. The have a simular reaction. If you have not replaced it in the last 50000 miles it is time to do so.
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if this car is on the cold start injector when it is defective. Injects additional fuel to the engine is still warm. Is it to feel warm by running more than normal gasoline smell?

Hello! Your symptoms tell me that you likely have a catalytic converter issue. When the converter becomes clogged, you will experience a significant loss of power and torque. This is often, but not always; accompanied by the smell of rotten eggs, another tell-tale sign of a converter issue.

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