Nuke

Are you SURE your speedometer is accurate? Also confirm that your odometer is accurate using highway mile markers. If the odometer is off AND if the "Fuel Used" value is off, it'll throw the onboards computations off.

What are you basing your fuel mileage on? The onboard computer? If so, begin calculating by hand but for that you'll need to know that the odometer is accurate. After you rule out those, then it's on to the engine...

scottmoyer

Could also be a plugged catalytic converter, O2 sensor.

gryon

Yeah im completely sure the speedometer is accurate because the previous owner was an old guy and he said it was completely stock. The car has high mileage on it so I guess that could possibly affect it as well. I'm going to try changing the air filter and fuel filter, and then I'll mess with the Catalytic Converter.

gryon

I also hear a clinking noise coming from my exhaust so maybe it is a bad catalytic converter.

Nuke

Before doing ANY mechanical work/replacements, ALWAYS ALWAYS be sure your data that's telling you that there's a problem is accurate. You imply that the data is accurate because the previous owner told you so. Really???

Get hold of a GPS, get out on the highway and confirm both the speedometer and the odometer, THEN start spending time and money AFTER the data is known to be accurate.

Kids these days...

Nuke

And if the data IS accurate, it could be many things:

1. Plugs
2. Wires
3. COPs
4. Injectors
5. Plugged air filter
6. Plugged fuel filter
7. Plugged cat
8. dragging brakes
9. Tire pressure
10. wheel bearings

There are more but that's off the top of my head.

outceltj

True that. You could also hand calculate to be sure as well

outceltj

Does your car have a slight rough idle. Do u smell gas ever

P51C

How can you hand calculate if your recorded mileage is off? Us old guys modify cars as well...in fact a lot more than young people do.

Stop everyone. Get back to the basics. It's not going to be tire pressure or something trivial like this. Mileage drops suddenly, I have suspicions but, I won't confuse the issue by speculating....and just change the stupid air filter, it's 10 bucks and eliminates that as an issue.

If you're still aggrieved:

Start with a code drop. This will tell you if anything has been detected wrong by the engine management comp. I'm assuming you don't have a check engine light currently.

Then pull the plugs and have a look what's really going on in the engine. These things used to be the only way we'd know what was happening.

Next, verify engine condition by running a compression test. You can buy these tester cheaply and it's a really good basic determiner of whether then engine's got life in it or not. You can find instructions on running this test online, easy.

With that data, come back here.

Nuke

When I see threads like this along with suggestions and then the OP never indicates that he has tried any of them but still whines, I can only assume that he has no idea which end of a screwdriver to use.

OP, as I stated earlier (twice, I believe), confirm that the odometer and speedometer are reporting accurately before anything. And using the onboard odometer to hand calculate without knowing that IT'S accurate will throw your calculations off, too. If this doesn't make sense to you, find someone that knows what to do. We want to help but become irate at those that won't accept any advice.