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Discussion Starter · #1 ·
I’ve got a 2000 Chevy k2500(obs) some backstory is that the previous owner rebuilt the engine and blew it up, so he disassembled it. I bought a new engine from AutoZone we got everything in. It will start and run smooth for about two minutes, then it will start running rough. When trying to drive it it only revs up to about 1800 RPM giving it more gas makes it backfire, but flooring it and letting off let’s you move it a little bit. I’m getting 52 psi fuel pressure when idling and 62 when tapping the gas
 

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Discussion Starter · #2 ·
I’ve got a 2000 Chevy k2500(obs) some backstory is that the previous owner rebuilt the engine and blew it up, so he disassembled it. I bought a new engine from AutoZone we got everything in. It will start and run smooth for about two minutes, then it will start running rough. When trying to drive it it only revs up to about 1800 RPM giving it more gas makes it backfire, but flooring it and letting off let’s you move it a little bit. I’m getting 52 psi fuel pressure when idling and 62 when tapping the gas
Also I will rev up to redline while in neutral
 

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Hates: Liver. Loves: Diesel
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Plugged catalyst, broken honeycomb in the catalyst, coolant temp sensor, bad O2 sensor or wire. Those are my three guesses.

Important thing though... backfire through the intake, or out the exhaust. One is lean, the other is rich.
 

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Discussion Starter · #4 ·
Plugged catalyst, broken honeycomb in the catalyst, coolant temp sensor, bad O2 sensor or wire. Those are my three guesses.

Important thing though... backfire through the intake, or out the exhaust. One is lean, the other is rich.
It’s straight piped so it doesn’t have any cats, it was backfiring out the exhaust
 

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Ok, so WAY more information is needed. One of the most important functions of the ECM's ability to function has been deleted. This is like saying, "I cut my hand off... why am I bleeding?"
 

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Ok, so WAY more information is needed. One of the most important functions of the ECM's ability to function has been deleted. This is like saying, "I cut my hand off... why am I bleeding?"
Well the truck has always run that way and the only oxygen sensor would be before the cat so don’t see how that would make much of a difference
 

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You said 2000. That is OBD2. The ECM uses both upstream (of the cat) and downstream (after the cat) O2 sensors to determine fuel trim. You have eliminated the catalyst and an entire sensor system from the ECM, so it can no longer function within the parameters of... well... anything it was supposed to be able to. That's like unplugging the MAF or the crank position sensor and expecting it to work.

When I say "more information is needed," I'm asking about the 3 zillion questions about how on earth this has been modified to even function. Is this a stock truck? Have you swapped to a carb? Is it a stock cam? You basically said 2000 chevy won't run right, and then you mentioned that you eliminated a massively important component for the ECM to even function.

Your truck was equipped with four O2 sensors. There are two before the catalyst and two after the catalysts. The upstream sensors are the primary means of adjusting A/F ratio. The downstream sensors report back on catalyst efficiency and further trim the fuel ratio for maximum reduction of emissions. You have removed your right hand and can't understand why it can't pick up a pencil any more. You have removed an entire emissions system and the sensors that are supposed to monitor it. End of story. I won't run right because it can't.
 

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Discussion Starter · #8 ·
You said 2000. That is OBD2. The ECM uses both upstream (of the cat) and downstream (after the cat) O2 sensors to determine fuel trim. You have eliminated the catalyst and an entire sensor system from the ECM, so it can no longer function within the parameters of... well... anything it was supposed to be able to. That's like unplugging the MAF or the crank position sensor and expecting it to work.

When I say "more information is needed," I'm asking about the 3 zillion questions about how on earth this has been modified to even function. Is this a stock truck? Have you swapped to a carb? Is it a stock cam? You basically said 2000 chevy won't run right, and then you mentioned that you eliminated a massively important component for the ECM to even function.

Your truck was equipped with four O2 sensors. There are two before the catalyst and two after the catalysts. The upstream sensors are the primary means of adjusting A/F ratio. The downstream sensors report back on catalyst efficiency and further trim the fuel ratio for maximum reduction of emissions. You have removed your right hand and can't understand why it can't pick up a pencil any more. You have removed an entire emissions system and the sensors that are supposed to monitor it. End of story. I won't run right because it can't.
It ended up being the water temp sending unit, runs like a dream, without the cats
 
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