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  #1  
Old 07-03-2013, 12:43 AM
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Horrible, I mean really bad, mpg on my hemi

So I have had my 05 5.7 jgc for 3 months now and man the gas mileage is bad. According to the specs its supposed to get 14 city 21 why, but if I drive it like a v6 i will be lucky to get 11 mpg city. Normally I get around 10.5 with moderate throttle. If I step on it at almost every light I get 9 mpg. On a 60 mile hwy trip I average 17.5 mpg at a constant 65 mph. So is it running rich or is this normal? I mean I didnt buy this car for gas mileage, but this is srt bad without the power. I tried seafoaming it through the brake booster, gas tank, and the oil (didn't help) and I also changed the oil with mobil 1 synthetic 5w-20(also didn't help). I fill plus gas (89 octane) every time, which should also help gas mileage but it doesn't . No check engine light. What do you think?
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Old 07-03-2013, 10:12 AM
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Im sure you never bought the Hemi for its mpg's (or I hope not), but I get your frustration. Your mpg's are actually right about where most people's are. All you can really do to see an improvement is slightly overinflated tires and stay off the skinny pedal. I try to keep the rpm's below 2000 on acceleration. Btw I have the 4.7, and still only get 13-14 city/ 19-20 hwy. If you ask most guys on this forum, those are pretty decent numbers.
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Old 07-03-2013, 10:33 AM
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Re: Horrible, I mean really bad, mpg on my hemi

i got the 6 and im getting about 16-17 city. Its a jeep.
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Old 07-03-2013, 10:40 AM
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Re: Horrible, I mean really bad, mpg on my hemi

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Originally Posted by Boomer914 View Post
i got the 6 and im getting about 16-17 city. Its a jeep.
I got the six too and I get 13.3 city up to 26 hi-way
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Old 07-03-2013, 11:45 AM
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Re: Horrible, I mean really bad, mpg on my hemi

05 hemi epa rating is 13/18 so you are right on. An SRT gets much worse mileage than that. Those city numbers are achieved only by slow accelerating and coasting to stops. MPG can be increased, but not by a lot. With 85mm ported TB, Apexi, and Diablosport Intune with CMR tune, I get 20 mpg HWY on the 87 OCT tune, and 21 mpg on 93 tune.
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Old 07-03-2013, 11:51 AM
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Re: Horrible, I mean really bad, mpg on my hemi

If you just got it, and there is no catch can installed, the throttle body is going to be all caked up with deposits. Remove and clean it carefully by hand using rubbing alcohol and a rag, and reset the ecu by removing the battery negative terminal while you are cleaning it. That will improve mpg a bit, and it will drive much better. This is also the time to install a catch can so the TB stays clean.
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Old 07-03-2013, 02:33 PM
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Re: Horrible, I mean really bad, mpg on my hemi

Like dmsfun says, do the throttle body cleaning and add a catch can, almost before anything else. Since you just recently bought it, I would highly recommend you do a complete major service and inspection of the entire vehicle, paying particular attention to the drivetrain. It doesn't have to all be done at the same time but, this involves changing all oils/fluids/filters (some you've already done I see), install good quality copper core, properly gapped spark plugs, make sure the air filter is clean, etc. etc.

While your FE is not too far off, you may have other issues too. Some of the sensors, especially if you have high miles and have contaminated the system with cleaners, may not be functioning quite as they should. The main ones to be concerned with are the IAT Sensor, MAP Sensor, and O2 Sensors. You can replace all of them for under $200, with the O2's being the most difficult to replace. If you have an exhaust leak, your FE will also suffer, as the O2's (if working properly) will sense a lean condition, and dump more fuel into the engine. With my mods. (in the summer non ethanol fuel), I usually get ~13-14 mpg in town, and ~20-24 mpg (normally ~22 mpg) on the highway....driving 65 mph in 4th gear, MDS on 90+% of the time. Also, remember, these slugs weigh in at almost 4800 lbs. without you and your stuff in the vehicle. Tough to do a whole lot better without some serious mods, especially in town. All of my mods, for the most part have been relatively non-invasive.....most I've had to do is remove the valve covers, rocker arms and front cover.

Edit: I just noticed you have an 05, so you should also check the ignition wire resistance to see if it is excessive.

Strongjeff, you cheat though....having headers on that cool running V-6. And, didn't you say your were 2WD also...~500 lbs. lighter?
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Old 07-15-2013, 10:14 PM
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Re: Horrible, I mean really bad, mpg on my hemi

Cleaned up the tb best I could without taking it off with a toothbrush and Isopropryl alcohol, didnt help gas mileage. Now I have slipped into 9 mpg in the city no matter how I drive. Infact if I drive it a little more aggressively, I get better mpg than if I drive it lightly.
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Old 07-15-2013, 11:10 PM
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Re: Horrible, I mean really bad, mpg on my hemi

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Originally Posted by jeepgcoman;

[I
Strongjeff, you cheat though....having headers on that cool running V-6. And, didn't you say your were 2WD also...~500 lbs. lighter?[/I]
lol I did and it is 2wd, but your guy's hemi will beat me in a straight line, but when the roads get twisty, I will win....but this isn't about my ride. my mpg's city sit in the 13's at best so it is not much better

EDIT: mine came in on the scales at 4280 @ half tank of fuel, since then ive removed an estimated 75 pounds
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Old 07-16-2013, 12:37 AM
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Re: Horrible, I mean really bad, mpg on my hemi

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Originally Posted by Strongjeff View Post
lol I did and it is 2wd, but your guy's hemi will beat me in a straight line, but when the roads get twisty, I will win....but this isn't about my ride. my mpg's city sit in the 13's at best so it is not much better

EDIT: mine came in on the scales at 4280 @ half tank of fuel, since then ive removed an estimated 75 pounds
I really doubt you will be able to beat us on the twisty turns either, since we have 4wd and other goodies we will be better able to keep the jeep under control on the turns and at a higher speed. I think the weight difference would be negligible. But you will win at the mpg game.
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Old 07-16-2013, 08:32 AM
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Re: Horrible, I mean really bad, mpg on my hemi

your missing the point, having the heavier engine puts more weight the front which induces under steer. also being 4wd will cause you to under steer as well seeing as how the 4wd drive systems on our jeeps is not made for handling. 4WD and AWD typically will under steer going into a corner, this is why 99% of all race cars are RWD. Case in point, my v6 is not only lighter, but its mounted lower and farther back then your hemi giving me a much better weight balance, and without 4WD it only helps the weight balance more. I will rather drive a car that is somewhat loose in the rear then one that wont turn going into a corner. One last thing, 500+ pounds is a little more then negligible in the corners. I give it to you it wont matter much on a straight because the hemi power makes up for it, but a litter car will always handle better.

BUT I agree with you on one thing...I do get better fuel mileage even if the difference is negligible
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Old 07-16-2013, 09:32 AM
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Re: Horrible, I mean really bad, mpg on my hemi

Sorry, Jeff, as much as I hate to, I'll have to agree with greenwayer, at least with mine. Mine is lowered with maybe 150 more rwhp than even a header equipped 6, has all SRT suspension (springs/sways) and Bilsteins all the way around. It handles like it's on rails, and I love driving it on the twisties, especially coming out of corners. I've got the transmission shift schedules set up so it downshifts with very little additional throttle coming out of corners. I love it. I'd love to drive yours though, because, as I think I told you, I still have a soft spot for the 6's. Next summer I am even thinking of entering it in the local Sports Car Club of America's twisty (slolum) competition at the fairgrounds. That should be a hoot.
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