need help figuring out why low gas mileage

[Fordman999]

so I dont know whats going on. I changed my Cat and installed 4 new 02 sensors and the P0420 code went away. now I'm losing A LOT of gas mileage and don't know why. it actually got worse after I changed my intake manifold gaskets and I think some hose is damaged but not sure which one if any. I did the starting fluid test and sprayed all the hoses and areas of the engine and no change in RPM when I checked all the hoses. Any ideas what it could possibly be? would the MAF sensor give a code? would a faulty EGR valve give a code? Would a smoke test assure the leak location? don't have any codes at all showing. No check engine light. I am losing coolant and I think its coming from my waterpump seal. SUV has 180,000 miles and never changed the water pump.

 

[Harpua216]

not sure of what type of engine you have, but a few things.

when was the last time you changed your spark plugs and wires? tune up etc?

You said you may have damaged a hose installing IM gaskets? you may want to investigate that whole install a bit. lots of stuff over there deals with your symptom.

did you switch gas stations? gas grades? maybe not, but i have gotten some junky gas in the past few years, i try to stay with better grades and bigger chain gas.

any performance issues?

I have an 04 mountaineer and have pretty terrible gas mileage right now, but i know it needs some TLC.

good luck!