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Crestwood1001 05-11-2011 12:22 PM

MPG Drop, Somethings Wrong
Alright guys, when I first got my 4.7L GC I would get around 14 mpg on average around town. Lately its been getting worse and worse and right now im sitting at 9.3 mpg no matter what I do. Im using the same fuel I always have so I cant figure out whats wrong. When I added larger tires I lost about one mile per gallon on average but it stayed that way. But over the past few weeks it been getting low.... any idea why?

jeepgcoman 05-11-2011 02:22 PM

Re: MPG Drop, Somethings Wrong
How many miles on it, when was the last tune up, and what mods., if any?

Bosibus 05-11-2011 02:39 PM

Re: MPG Drop, Somethings Wrong
Would larger tires throw your MPG meter off because of the size of the tire?

SvenskaJeepGuy 05-11-2011 04:06 PM

Re: MPG Drop, Somethings Wrong
you are not getting worse mpgs, your speedo is off from the different tire size. that messes up the computer

lll2for3lll 05-11-2011 04:23 PM

Re: MPG Drop, Somethings Wrong
My info center shows that I only lost 2 mpg since my lift and tires and it has stayed that way every since. Something is definitely wrong.

Other guys with lifts and larger tires without a speedo fix will tune in and and agree because 31-32 inch tires will not throw the computer off that much.

Crestwood1001 05-11-2011 04:25 PM

Re: MPG Drop, Somethings Wrong
They are not that much bigger, and I know that would throw it off but there is no way it would throw it off and then keep going down. Its got around 76000 miles and the only mods are bigger tires and a magnaflow exhaust

soontobesrt 05-11-2011 06:14 PM

Re: MPG Drop, Somethings Wrong
Honestly, I wouldn't be too surprised it its the tire/exhuast combo. Those two combined may result in a net loss of 2-3mpgs! So 9.3 under heavy throttle may be right! People become shocked when MPG drop into single digits but hey, mod will do that. A Stock SRT8 sees that under city driving if you now how to get on her. Don't be surprised if she only gets 9-10 city now, highway you should probably see less significance, maybe 1mpg or so less, try resetting and running her on the highway and compare.

lll2for3lll 05-11-2011 06:54 PM

Re: MPG Drop, Somethings Wrong
Ummm....I still say there is something wrong. If he's been driving like he always has, then there is definitely a need for a tune up. I've been 32" tire for quiet some time now and it has never gone outside of the 12-14 mpg range.

Spark plugs
Manually clean TB
ERG valve
PCV valve

Other big wheel Jeepers should chime in.

Crestwood1001 05-11-2011 09:06 PM

Re: MPG Drop, Somethings Wrong
I dont get on it, I baby it and its been going down. I know i should expect a loss with bigger tires, but when I got the exhaust I gained a few MPG. I guess im gonna have to do a tune up.

Marlin 05-11-2011 09:21 PM

Re: MPG Drop, Somethings Wrong
A lot of people didn't read the first post properly, he quite clearly said, "When I added larger tires I lost about one mile per gallon on average but it stayed that way."

So yes, there must be an issue, but diagnosing it over the interwebs is very hard.

Does it feel like it's lost power?
Is it acting up at all?
Is there any fault codes after the key dance?

It could be anything from a sensor gone bad, to a blocked/melted catalytic convertor.

Scottina06 05-11-2011 09:32 PM

Re: MPG Drop, Somethings Wrong
I think you have a serious case of the leadfootitits.....and wont or cant admit it.....LOL...J?K!

could be clogged cat, egr going bad, plugs etc etc

Crestwood1001 05-11-2011 09:52 PM

Re: MPG Drop, Somethings Wrong
I think it needs plugs, and i havnt noticed anything wrong, it feels fine. And i baby it unless im on my way to the station for a fire call, which is a half mile strait away from my house, so I get on it hard then, but thats about it lol

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