Hey guys. I have a 90 firebird 305 tbi and for some reason I'm getting under 9 mpg. I tried searching for an solution on here but haven't seen anything yet. And I really need help

 

CE light? codes?

possible coolant sensor telling the ECU it is -40dF.

 

Ok here's the codes I got. It's about 20 degrees outside today so idk if that would trigger any of these.

15.low temp at coolant sensor
23. Low temperature at manifold air temperature sensor OR Throttle position sensor error
33. High voltage (low vacuum) at mass air flow sensor (or MAP sensor)
44. Oxygen sensor lean

So this means I need to replace the coolant temp sensor right? And if so, which one. I know when I used to work on Honda's they would have two but idk if these cars do as well.

 

i think you have a vacuum leak at the throttle body. and have you checked coolant level. i was getting really bad fuel mileage before and it was the coolant sensor.

 

Speaking of vacuum leaks, did you finish that IAC mod for the TB?

 

you know what i never did that. bought a bunch of other parts that i still have to get finished.

 

How do you check for a vacuum leak?

 

Make sure your engine is getting up to proper temp. The coolant temp gauge should be close to the middle, not hanging near C. This really impacts fuel mileage. Cooler running is not better for good mpg.

 

Spray areas you think might be leaking with carb cleaner. You'll know when you hit it because it'll cause your engine to idle higher

 

check the sensor with a volt meter....If you suspect it is 25 years old I might just replace it....

 

Will do both. I get paid Thursday so I'll post up if it worked then. That's to all.wish me luck

 

Ok so I checked for vacuum leaks and found none (which I suspected cuz I just cleaned the whole throttle body and replaced all the gaskets) then I replaced the coolant temp sensor,dizzy cap and rotor,spark plugs and wires(since the car has been sitting for 8 years OUTSIDE),started her up cold no problem(which is a first for this car) AND no ce light! Took her for a spin to the store and she's running better than ever. Thanks everybody!