my truck runs rich when it is cold like so rich you wold think it is a oil burner. but when it runs for about 2-3 min it is better but i am still only geting 11 mpg it yous to get about 13-14

 

Well can you describe to us what you've done to the car lately, over time and what recent events have occurred during this shift in milage?

 

ok was getting realy bad mpg like 9-10 mpg so i got a new holley tbi then it jumped to 13-14 mpg was like that for about 4 months then i lost a fuel line so i pulled the tank and had to put in a new sending unit at this time i put new fuel lines in. so after that i was like ok this thing should be ok for a bit then it started to run like crap when it was cold and such the motor is all stock except the tbi and i have a k&n off road filter on it. i tried a tune up no help. and it is a truck not a car so the 13-14 mpg was nice but now i am lucky to pull 11.5 mpg. some one please help me i dont want to have to drive my iroc in the snow.

 

If you're running super rich at idle, you may just be running rich over all.. try dropping the fuel pressure and see if that helps. Also ensure your fuel filter is not clogged and the return line is not kinked or jammed.

Check your plugs, running rich would foul them and make the problem worse.

An O2 sensor may also be needed as it gets fouled up too when too rich.

 

If the vehicle is bone stock and doing this then its usually either the O2 sensor or the Coolant temperature switch. Both can easily cause the problem. Fuel pressure is unlikely unless you have kinked the return line some where. But try those 2 and see how it runs.

 

i thought that the O2 sensor was only used when the temp cam up and the car went into close loop

 

But engine is still getting crappy mileage once it enters closed loop. If its running that rich then the 02 sensor is taking a beating along with the CAT.

 

true i didnt think of that

 

If it smells super rich at idle, then odds are you may these things going against you...

return line may have a kink causing pressure to be up.
fuel pressure is higher than it should be
plugs, o2 sensor are fouled up so much that its not enough to spark the mixture properly, thus more fuel is added to the system since o2 detects issues and the problem confounds itself further.

At start, the car goes through an enrichment mode, but its never usually enough to cause any problems, smells or damage to the system. That's why your pressure may be at fault.

 

ok i got a net temp sensor and i checked for kinks there where none so i am still having probs with it

 

wait, i thought it was normal for your rpms to rise to about 1500 for a couple minutes then fall to normal idle after a cold start.

 

it is but there shouldnt be black smoke coming from your tail pipes