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Engine flooding while driving?

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Rocky91

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Rochester, NY
My engine has been running extremely rich since I rebuild the top half about a month ago. Twice in the last week it has flooded after a few minutes of driving. It's a '91 TBI 350 and the only thing that has been changed on it is a colder thermostat. I going to put the stock thermostat back in it today, but what else could cause my engine to run that rich? I don't think that a thermostat alone would make it run so rich that it stalls out? The wheather is starting to get cold around here, that is why it started acting up this week. What can I do to lean the engine out before winter hits? Any help would be appreciated. Thanks.
 
the coolant temperature sender in the intake manifold is responsible for the mixture in the engine as it tells the ecm what temperature the coolant is. if you have a problem with that sensor or the wiring to it, it could cause the ecm to think it is cold all the time and run rich (like the choke is stuck) it could be the sensor itself or sometimes the connectors inside the plug get loose or damaged and don't make good contact.
 
I replaced the temperature sending unit with a brand new one when I rebuilt the engine last month.
 
First of all you need to put the stock 195 degree thermostat back in . The computer is programed for a 195 degree stat. a colder stat will screw up its operating settings.
If its running ad rich as you say there should be some trouble codes stored in the computers memory.
You really need to bring these uo to help fix it.
More info on trouble codes (clicky):GM trouble codes
The ALDL connector is located under the steering colum.
Bring up the codes. if you cant figger it out. post the code numbers. it will be easier to help you out.
 
The only trouble code that is in there is a back O2 sensor that's been bad since I bought the truck. The SES light was on constant until I rebuilt the engine and now it doesn't come on at all.
 
If one of the O2 sensors is bad. the computer puts the system in open loop(default) mode. Usually this results in a rich mixture, Causing bad gas milage and other driveability problems that happen when it is running rich.
When in open loop mode the computer diserguards the input from all the sensors and runs on a pre programed setting.
 
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