Which is the more likely culprit for sudden bad gas mileage?

an o-2 sensor going bad is the most common cause for it ,but you still need to get the computer scanned on it to be sure,there's no way i can tell you for sure,but that is one of the most common causes for one getting bad gas mileage all the sudden,sooner or later the check engine light should come on also if its a bad sensor on it,good luck with it.

Yes, your fuel filter and 1 or both ( if you have 2) o2 sensors going bad will destroy your fuel mileage. You are on the right track though by changing the stuff you did already. Buy a bottle of Lucas fuel system cleaner and pour it into your tank and give it about a week and see if there is any improvement before purchasing the O2 sensor(s). Hope this has helped you.

Reasons For Bad Gas

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RE:

Which is the more likely culprit for sudden bad gas mileage?

I have a 95 Dodge Neon, and before anyone tells me it's having problems because it's a neon, I'm well aware the faults of thiese cars, but it's our only, so...save it. Sorry, I had my plugs, plug wires, coil, valve cover...replaced a few weeks ago, the mechanic said it would help my...

I suspect a stuck choke. If so, it could be a quick and easy fix.

Try a good shot of carburetor cleaner in the choke.

If your car has a carburetor(not fuel injected), it might have a steel heat riser tube leading from the exhaust manifold to the carburetor. As the manifold heats up heat rises up the tube to the carburetor to knock off the choke. As the car ages the tube rusts out, heat does not go to the carburetor and gas mileage goes down the toilet. This happened to me(but I don't remember which car.

If this is the problem auto supply stores sell inexpensive repair kits which are quick and easy to install and work like gangbusters.

O2 sensor will affect how rich the mixture is . Fuel filter if blocked partially will cause low fuel pressure but should not cause high gas consumption.

Hooking a diagnostic computer up to the car should tell you at once if the O2 sensor is the problem .

hey i owned a 1995 Neon some years ago it wasn't all that bad. I would say you might want to make sure you have covered the basics like a new air filter, then move on to the more complex things like restrictions in your exhaust flow like a catalytic converter. Another thing to have checked is your coolant to make sure it is operating at the correct temperature, make sure its shifter correctly through all gears and the torque converter is functioning correctly. as you can see it can be a lot of things and one more basic thing is the weather if you live in cold climate and the temps are dropping in the single temps and lower its going to suck a noticeable amount more of gas.

I doubt if it is your fuel filter because a bad filter would cause your engine not to get fuel.

It could be the O2 sensor. If it is bad you could be running too rich.

Don't neglect tire pressure. In the winter when the temperature drops your tire pressure will drop because cold air is more dense. Underinflated tires could rob you of 2-5 mpg easily.

You could also check the air filter.

O2 sensor and possibly the catalytic converter may be partially stopped up....How many miles on the vehicle since it is 13 years old you may want to have these things checked.....a stopped up fuel filter would cause an erratic running....like running for a few miles then quitting and starting right back up.....

bad tank of gasoline could be to ,would say check air filter first or change it its simple ,then check milage if not helped change spark plugs and wires and while doing it replace the fuel filter to as all 3 both use each other in combination ,if it was 02 sensor light shoulda come on etc as or the convertor it could be getting pluggedup etc but check it last ,this should help .And yes tires air pressure helps alot ,as well as not buying bad gasoline does to