I'm at the end of my rope with this lt1.
Every time you start it , cold or warm it runs super rich. Black smoke and of course runs rough for 30 to 45 seconds then runs better. No check engine light, I have changed damn near every sensor on it except for the injectors, by the way fuel pressure is 40lbs and no leak down.
Could the ecm be causing this?
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It could be time for a trip to the dealership. I'm not sure if that is an ecm issue, sounds like a temp sensor to me. Keep us posted.

 

That was the First sensor I replaced.
Dealer doesn't know.
I've already talked to them.

 

This is why I hate computers, try to find a small shop that has a real diagnostic system. Not a hand held parts store special. You will need to leave the car overnight so it can be plugged in when cold. Then they will be able to actively read the system as it warms up to see what is triggering the excessive fuel.
The car either thinks it's seriously cold out or it's reading too lean. A vacuum leak can cause this as well as a misreading O2 sensor.

 

It could be many things, Even in open or closed loop it still shouldn't run that rich. Rich conditions can be hard on o2 sensors and might need to be replaced if you haven't already. 02 sensor could have a bad heater, Have you checked for error codes stored in the ecm? There are many services out there that can check your ECM if you send it to them. Have you replaced the ecm engine temp sensor or checked it? It might think it's always cold

 

All sensors have been replaced. Temp sensor was first on the list, 02 sensors don't take effect until engine is warm .
I will replace them after the start up is fixed.
New ECM should be here any day now.

 

Sounds like you have everything covered, let us know how it turns out.