LOW gas milage - many potential symptoms

[marewrath]

ive had decreasing gas mileage over the past few months, down to about 15 miles a gallon, from around a mure acceptable 30; I've gotten p0420 code - turned it off 2 or 3 months ago, came back last week.

have gotten 10 million different diagnosis from mechanics that were all postiive thye knew the problem;
exhaust is very rich.... ive put in fuel cleaner, was gonna clean/possibly change my o2 sensor, but then some guy came by and suggested i do that instead. had my cat welded back over a leak back around when it first started happening (for what was obviously an exhaust leak); got spark plugs for a tune up but havent put them in yet, was gonna up t anew fuel filter in too. one guy tested my o2 sensors and said they ere switching back and forthe fine; another did something more direct and said the downstream was recruiting extra gas.

also got an alignment...

this monrning i noticed white(ish?) smoke billowing from my exhaust for about a minute on starting; not sure if this has happened before, didnt again the next two times i started it.

hard start, but i believe ive had that since i got it a year ago.

im trying to fix the gas before anythign else cause HELLO $4 a gallon...

 

[cgpEJ6]

Change your spark plugs and see where you are at, it's a lot more likely that's your problem than any of the other things you mentioned.

 

[RonJ]

The catalytic converter is almost always destroyed by the engine running rich. The most common cause of running rich is a failure to do regular ignition system tune ups. Replace the plugs, wires, cap, and rotor and then adjust the ignition timing to spec. When the tune up is finished, replace the cat.