Well I've had a really big drop in gas milage latly. It ran like a champ since I put the exhaust, intake and seafoamed it. I was getting 22MPG average on 235/70 (28") I have since put 30" mud terrains on it which would result in SOME drop in milage. I am not getting 16 HIGHWAY. It's horrible. My guess is either the cat went to hell. Haven't had time to take a look at that yet. But the thing is I also think I have a loose motor mount at this point. My K&N keeps coming off the top of the throttle body (i beleive due to extra play in the motor mount) could this increase in air thats not going through the MAF be causeing a drop in milage? It only comes loose it just sits on top the throttle body not like completly off or anything. The filter also looks relativly clean.

The only things that I can think of:
Bad cat
Air intake thing
fried/disconnected o2 sensor
crushed exhaust pipe

Is there anything else I am missing? I'd like to have an idea on where to start when I get a chance to go home next. For now it does alright I'm just putting around town with it. Maybe go hunting once a week so gas isn't killing me too bad. I just need an idea of where to start. Thanks

 

Take a rubber mallet and smack the cat, if its bad youll hear it, it will break easily if its not broken already, a clogged cat will glow your y pipe.


Bad 02 will throw a code.

exhaust might be crushed but I doubt its crushed that bad where it dropped you that much.

get a crowpar/prybar and flex the engine when its off, you can tell if its got a broken mount or not without having to start it. Might be able to shake it by hand as well.

Hows the exhaust smell?


how long since a tune up?

How long since a fuel filter was replaced on it?

Have you checked the wires? mainly the coil wire, for cracks?

Bad vacuum lines might also be a possibility.

 

A clogged cat will cause some serious power issues higher in the rpms (typically over 2000rpm). You would be complaining about more than just a drop in fuel mileage.

Now your tires if wider and taller will definitely have an impact on the fuel mileage.

I would suspect the popping off of your intake to have more of an impact on the fuel mileage as any air that enters behind the MAF sensor will decrease the overall efficiency of the motor. A slight vacuum leak can impact fuel mileage.

Also, another thing to note is if your state has already switched to the winter mix fuels. Winter mix fuels have more addatives to help in cold starting, but one of the down sides is often lower fuel mileage.

It may just be a bunch of contributing factors that are all combining to create this drop in mileage. Only one that I can see straight off that should be remedied is your intake coming loose.

Other areas to check would be your plugs, possibly run a can of fuel injector cleaner through a few tanks and make sure that your EGR valve is clean and unobstructed.

 

I didn't think about the plugs. I don't think I changed them after I seafoamed it. I'll have to check those. I don't think it was fuel at all. I was running premium for a few tanks untill I saw a huge decrease in gas milage then quit because it isn't worth it if soemthing else is robbing me. I'll also hit the cat a couple of times with the ole' rubber mallet see if she makes any noise but she still seems to have full power at upper RPM's and doesn't have any problem getting up and going at all. I am pretty sure the motor mount is crap because the intake shouldn't fall off and she tourqes quite a bit when I put her in drive. I can see it when I have the hood open. It's raining right now I'll see what I can do for now hopfully it stops raining though I don't have a garage at my apartment to work in.

 

I think I narrowed it down to the plugs. The air filter has been holding on since last time I filled up and I ran through a 1/4 tank only going 62 miles. About 30-40 of it was either 2 tracks or back roads cruising at 60. And like swart said i don't really have the symptoms of a bad cat. I'm still sure the motor mount is bad or pretty near it but seems like the plugs would be most likly since i ran seafoam through it and never changed them out. It's not missing or anything just crappy gas milage.

 

I put on a Gibson exhuast and a couple of months later the cat blew. I changed the cat and bam. Make shure you change all of your o2 sensors just incase becuase a bad cat overheats the exhuast and harms the sensors! Don't take to long to change your cat it cuase it might clog up you new exhuast too!

 

so what am i listin for whne i hit the cat cuase i think mine might be goin casue it aint got the power it use to in the high end.

 

Stuff moving around inside it, if its broken you will hear it with just a smack or two of the cat, usually the first smack you can hear that its not "solid"

 

Id be lucky to get 16mpg

 

Tire size is one of the biggest contributing factors to decreasing fuel economy. The more rubber that is contacting the road, the worse off you are. That's probably the main culprit.