Have a 91 firebird 305 it's tpi I believe but I'm geting about 4-5 MPG what are possible reasons I need to look into fix this?

 

Try running your fuel lines and check for a leak somewhere. Do you have a strong gas smell?

 

Ill see if I can find one no real strong gas smell could it be fuel filter or something that regulates the fuel if so what

 

maybe you live in a bad neighborhood ?
http://gasbanditblocker.com/
Some Walmarts carry them.

 

There are some rubber lines at the tank that can dry out and crack, thus leaking. The fuel pressure regulator could be a problem, but that's not too likely. Its possible that it could be leaking at any joint in the system once the system is pressurized, most likely under the car because a leak under the hood would likely result in a fire. 305sbc could be onto something too.

 

So I replaced the map sensor. And temp sensor still bad gas mileage anything else I should look into

 

The engine needs to run at 190-200* to get the best mpg. Get a good t stat in the 195* (stock) range.
Hook up a fuel pressure tester gauge, the psi should be 35-42psi or so running, It should hold psi when engine is off. If it doesn't then the injectors might be leaking, a bad regulator, line leak, ect.
Check ign. timing & make sure it advances when you rev it.
Plugged up exhaust from a bad cat.
Loose ecm grounds.
Vacuum leaks.
A dead o2 sensor.
Any codes?