My car is a 1988 GXL and I am only getting about 10mpg. Its a brand new engine (has been broken in properly) and new trans. The one thing that isnt stock is the exhaust which is freeflowing. Any ideas?

 

If you haven't done so already, install a new o2 sensor and get your fuel injectors cleaned.

 

It's the exhaust which is free flowing I had a 91 and it did the same thing.
Put the racing beat exhaust on it and got like 19 mpg and it was a lot quieter.

 

Ya I changed my o2 sensor and my injectors are new. Looks like though ill haveto try changing exhaust.... YAY

 

I had a new O2 sensor put on and mine was still getting poor gas mileage. I took it to another mechanic and he put in a NEW one because when the other one was installed the wires were all twisted. He said they are extremely delicate. My gas mileage is now back to normal!