I have a 98 Blazer with 115K on it. Over the last 6 months I have replaced the coil, cover, plugs, and wires as well as the spider and fuel pump (to fix the wonderful fuel guage). After the fuel pump, I noted a significant drop in MPG as well as a coolant odor. Could my mixture be too rich and setting up some type of overpressure? Am I missing steps here? Are there adjustments to be made after replacing most of the fuel system? (BTW both the pump and the spider are AC) Any help would be greatly appreciated.

 

Has the weather recently turned cold at the same time you noticed the fuel economy drop? Do you drive short trips? If you drive short trips in cold weather the fuel economy will drop. Next, what temperature is your engine running at? In cooler weather the engine needs to run at full thermostat temperature for the computer to adjust the mixture properly. You should be running at least 190 degrees after the engine has run a while. If not, install the OEM Delco thermostat or other brand name 195 degree thermostat.