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Old 11-01-2011, 09:30 AM
Fish79 Fish79 is offline
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Why is my gas mileage so bad?

Ok I bought a 2008 RT Charger, and while I am fully aware that I did not buy a Prius, it seems like my MPG's are uncharacteristically low based on what I have been seeing other people getting.
Now I purchased the Charger used and the only physically noticeable modifications when I got it was a K&N Cold air intake and a set of Pypes dual exhaust, but nothing I read suggested these alone would greatly rob my gas mileage.
I am running 91 Plus in it and I checked the on-board fuel economy reader against actual calculations and it is accurate. I spent a week driving (mostly city) but as responsibly as possible, never taking the tac over 1,800 rpm's and not getting there quickly either, at the end of the week I was at 10.4 MPG's and I have pinned cruise at 60mph on the highway for 15 miles and was getting 16 MPG's.
I'm just wondering if I am stuck with this, or if anybody can think of something the previous owner may have done to rob my gas mileage, and if so can it be reversed?
Thanks for any help!
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Old 11-01-2011, 09:35 AM
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Mileage?

First thing I'd do is check the plugs and change, if necessary, to the champion coppers.

They're supposed to be changed every 30k miles.

Also, no reason to run 91, unless you have a tune installed.

Is MDS enabled and working?
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Old 11-01-2011, 09:36 AM
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Only thing I can think of is that the R/T's are supposed to run 89 octane, unless you have your car tuned for a different octane.
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Old 11-01-2011, 09:43 AM
DUG's Hemi DUG's Hemi is offline
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I have a little bit of the same thing going on. I lock in my cruise control at 60 mph, and reset the MPG monitor, on even to slightly down hill grade. It showed me getting 18 mpg, shouldn't that be 23-25????

Also, my car sounds like it is reving hard while cruising around 77mph, and is around 2500-3000 rpms, are these cruising rpm's on par with others here???
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Old 11-01-2011, 09:43 AM
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Quote:
Originally Posted by Fish79 View Post
Ok I bought a 2008 RT Charger, and while I am fully aware that I did not buy a Prius, it seems like my MPG's are uncharacteristically low based on what I have been seeing other people getting.
Now I purchased the Charger used and the only physically noticeable modifications when I got it was a K&N Cold air intake and a set of Pypes dual exhaust, but nothing I read suggested these alone would greatly rob my gas mileage.
I am running 91 Plus in it and I checked the on-board fuel economy reader against actual calculations and it is accurate. I spent a week driving (mostly city) but as responsibly as possible, never taking the tac over 1,800 rpm's and not getting there quickly either, at the end of the week I was at 10.4 MPG's and I have pinned cruise at 60mph on the highway for 15 miles and was getting 16 MPG's.
I'm just wondering if I am stuck with this, or if anybody can think of something the previous owner may have done to rob my gas mileage, and if so can it be reversed?
Thanks for any help!
Okay a few quick questions to help get some better answers:

Do you have a Predator? If not, you should be running mid-grade gas which is 87-89. Using 91 is high without a tune.

Are there any codes (engine light on)?

How long have you had the car?

How many miles on the vehicle (round number, doesn't have to be exact)?

Do you have service records and/or Carfax or other vehicle history report?

My worst gas mileage is 17mpg and that is when I'm doing really dumb things along with stop/go city driving. 10mpg tells me something is really wrong. Answer those questions and whatever else other people ask and perhaps we can give you an idea of the issue, but as of right now it looks like you need to take your car in to be checked out.
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Old 11-01-2011, 09:48 AM
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Quote:
Originally Posted by DUG's Hemi View Post
I have a little bit of the same thing going on. I lock in my cruise control at 60 mph, and reset the MPG monitor, on even to slightly down hill grade. It showed me getting 18 mpg, shouldn't that be 23-25????


Also, my car sounds like it is reving hard while cruising around 77mph, and is around 2500-3000 rpms, are these cruising rpm's on par with others here???
No. The best I have gotten was 24mpg and that was cruise set to 75mph for a 1200 mile round trip. I haven't gotten that mpg again since. My average is 17-20 depending on how I am driving. Plus the AWD R/T is a pig even to the already piggy R/T lol.

The rpms are in the right zone. Your FM's are going to exaggerate the sound at cruising speed big time.

I'm assuming these were serious questions and not being silly

Last edited by Dreadnought; 11-01-2011 at 09:50 AM.
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Old 11-01-2011, 09:54 AM
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Quote:
Originally Posted by Dreadnought View Post
No. The best I have gotten was 24mpg and that was cruise set to 75mph for a 1200 mile round trip. I haven't gotten that mpg again since. My average is 17-20 depending on how I am driving. Plus the AWD R/T is a pig even to the already piggy R/T lol.

The rpms are in the right zone. Your FM's are going to exaggerate the sound at cruising speed big time.

I'm assuming these were serious questions and not being silly

I get (got)30mpg, but that's with 2.65 gears on the 2009+ engine.

It's gone down a bit with the 3.06 gears.

AWD has different rear gears than RWD... 3.42 maybe? That'll kill your MPG. (plus the added friction from the transfer case and drive line.)
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Old 11-01-2011, 10:16 AM
Fish79 Fish79 is offline
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No Predator so I will drop it down to 89

No Engine lights on

I've only had it a month

58,000 miles on it

I have the Carfax somewhere, nothing stood out as being wrong or shocking outside of a joint needing replaced, but that went bad because the guy put a set of really cheap ventilated brakes on that gave the car a terrible shimmy when you stopped.

I have a friend who works at a Chrysler dealership so maybe I will take it in and get the plugs checked. I have noticed that if i hold the RPM's in park around 1100, every 2-3 seconds it will rev itself up to 1300 and drop right back without me moving the pedal at all.

I'm not going to lie, I am not the most mechanically inclined so I don't know how to check if the prev owner had a tune installed or not, would hooking it up to a computer be able to tell me?
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Old 11-01-2011, 10:25 AM
DUG's Hemi DUG's Hemi is offline
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Quote:
Originally Posted by Dreadnought View Post
No. The best I have gotten was 24mpg and that was cruise set to 75mph for a 1200 mile round trip. I haven't gotten that mpg again since. My average is 17-20 depending on how I am driving. Plus the AWD R/T is a pig even to the already piggy R/T lol.

The rpms are in the right zone. Your FM's are going to exaggerate the sound at cruising speed big time.

I'm assuming these were serious questions and not being silly

I was being serious lol, but I guess the AWD is what I am not used too, I just bought this car a month ago and every time I let off the gass it immediately starts slowing down like I am braking, (assuming this is AWD mixes w auto trans). I just have to get used to the new car i guess...lol
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Old 11-01-2011, 11:02 AM
Fish79 Fish79 is offline
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I looked into the service records, I don't think he ever got the 30k plugs changed and I am now at almost 60 k anyway so I will get them changed asap. Hopefully that helps. You guys are awesome btw, thanks for the help. I'll keep ya posted and post a couple pics as soon as I can give her a good bath.
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