What kind of tune do you have installed on the ECM? Where is your O2 sensor mounted? It sounds like it is staying it warm-up mode, and not going into closed-loop. It is dumping fuel, and that is why it is running rich. How rich is it? Does the EFI system have a laptop connection and a dashboard so you can monitor the sensors?
What is running hot? 200, 210? Newer engines are designed to run a little hotter than older cast iron engines. An LS1's run temp is 200-210, 220 is getting hot, 230 is aproaching the danger zone. How hot has it gotten?
I have a shop in Stillwater, let me know if you want to bring it up. That goes for you too, Cowman.
210 is not that bad, its warm for sure, but it will live at 210, cast iron and all.
I don't know much about that howell system, but it seems really low-buck. You need to be able to monitor the sensors, that is a key point. What kind of radiator are you running? If it is the stocker, it could be plugged up. Do you know anything about the motor itself? What kind of shape was it in when you swapped it?
We had a Mustang with a rebuilt 302 and a high-dollar EFI system and it was fouling plugs within a 100 miles or so. In the end, we upgraded to a learning ECM, and that fixed it. I suspect your problem is in the computer or you have a bad connection on your O2 sensor. The whole running hot thing is likely a secondary issue.
Is it throwing any codes?
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