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Unread 12-26-2010, 07:03 PM   #1
mavster
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Join Date: Dec 2010
Location: JFK, New York
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Just joining the club & I have a few questions (related to fuel economy).

Well First, I'd like to say Howdy all!

Just picked up a CPO 2008 Jeep Grand Cherokee Overland edition. I absolutely love it, including the hemi.

The process was smooth, though I find myself having some issues with my dealer. Somethings missing here and there and a cracked bumper that was fixed and now the crack has reappeared.

But I do have a major issue; something just isn't right with it.

My Fuel economy is in the toilet and I can't figure out why. I mean I have a hemi I know I'm not going to get 20mpg; but I do a mix between City (minor stops and go's between stop signs and lights to the nearest parkway or expressway) & Short highway bursts.

I'm struggling to get 10mpg, something just isn't right..and being new to the engine I have no idea where to start looking. I keep the mpg indicator active and notice when the "Fuel Saver" mode appears, but even then it's a leap to get 13mpg (doing anywhere between 40 to 60mph @ < 2k rpm on the tach).

So I was wondering if anyone had any tips?

Also if anyone can help me out with pictures of certain things, so I can show my dealer inorder to get it replaced accordingly.

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Unread 12-26-2010, 07:08 PM   #2
Devilsmed98
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Well first off welcome to the club. Sorry to hear your having such problems with your new Jeep.

MPG: I hate when people complain about their Jeeps not getting good MPG but yours seems to have pretty terrible mileage. How many miles are on your jeep? It could be anything from the spark plugs, to air filter, to bad o2 sensor. What gas are you putting in it? Are you letting it idle a lot with remote start in the driveway? When you do your daily commute how long is it? (Is it getting up the operating temperature in the cold). Are you hand calculating your MPG or just going off of the EVIC (which I believe is the last 30miles of driving).
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Unread 12-26-2010, 07:18 PM   #3
mavster
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Very good questions; and I'd like to thank you for welcoming me...It just hit 32k miles.

See I don't think the dealer did the spark plugs at the 30k interval (It was a trade in).

I started with 89 as required; and I do admit I beat on it a bit with a few high revs (figure 4 to 5); but I went from a full tank to under half tank only doing 80 miles of travel (40 of those were straight highway, taking my time doing about the speed limit...a little quicker, but again not high revving).

I don't let it idle excessively, figure at the most 3 minutes.

Thanks again
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Unread 12-26-2010, 07:25 PM   #4
Devilsmed98
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Hmm very interesting. I'd say definitely bring this to their attention, ask them to show maintenance records on it if they have any. If you can yourself, pull the plugs and inspect them. I have a 4.7L so I can't really comment on what type of plugs they are and what they should be gaped at, but I know with mine that they must have specific plugs or the fuel mileage will be depreciated terribly.

Also, check the air filter while your in there, check the oil. My mom's 2011 Hemi (same engine as yours *I believe* or maybe that was 09-11. And she is getting 13-14 mpg city driving with using remote start a ton.

How's your driving style also? Aggressive? Right lane driver? You may want to try resetting the MPG on the EVIC also.
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Unread 12-26-2010, 07:34 PM   #5
lll2for3lll
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Have them replace the bumper rather than a crap patch job.
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Unread 12-26-2010, 07:46 PM   #6
conyersWK
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This just happened to mine except it was in the range of 8mpg with the usual being 12 to 13. Figgured somthing was wrong so i had it checked out... turned out it was a disconnected vacume pump. i think.. it was a while ago.
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Unread 12-26-2010, 09:27 PM   #7
mavster
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Would spark plugs heavily affect my fuel economy?

Is the Champion 570s Copper Plus recommended? What about NGK V-power?

Also; Can someone post an image of their rear cup holder, located below the seats? I think I'm missing something there, and want some proof before I bring it up with my dealer.
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Unread 12-26-2010, 09:38 PM   #8
Devilsmed98
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Quote:
Originally Posted by conyersWK View Post
This just happened to mine except it was in the range of 8mpg with the usual being 12 to 13. Figgured somthing was wrong so i had it checked out... turned out it was a disconnected vacume pump. i think.. it was a while ago.
That was going to be my next guess after plugs/filters and all that. Mavster do you know a little about engines or anything? Maybe try checking the vacuum lines while your under there also.

Quote:
Originally Posted by mavster View Post
Would spark plugs heavily affect my fuel economy?

Is the Champion 570s Copper Plus recommended? What about NGK V-power?

Also; Can someone post an image of their rear cup holder, located below the seats? I think I'm missing something there, and want some proof before I bring it up with my dealer.
The wrong spark plugs could heavily affect your fuel economy if your using the wrong type since the cylinders would be predetonating and then the computer would be constantly changing the timing trying to keep them all in sync.

The Champion 570s are the recommended ones. Being that you are new to the forum and the Jeep world I am going to let you in on a little secret.

It's called WKJEEPS.com It's pretty much like everything you would need to know about anything you'd need to know with our jeeps.

And here is a link to the spark plugs page: Jeep Grand Cherokee WK - Spark plugs
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Unread 12-26-2010, 09:47 PM   #9
mavster
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I'm pretty technically inclined, and my old man is a full ASE...but with it still under warranty pretty weary with touching it.

I have to call my dealer tommorrow, to get a full service history on the vehicle... I literally just got the thing last thursday, and I'm already over $100 in gas on it (got the thing on empty, $65 to fill it up and another $40 from half tank after driving 80 miles)...

The above poster is right, I'm going to force them to change the bumper now, the quick fix is already showing a break.
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Unread 12-26-2010, 09:53 PM   #10
Devilsmed98
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Quote:
Originally Posted by mavster View Post
I'm pretty technically inclined, and my old man is a full ASE...but with it still under warranty pretty weary with touching it.

I have to call my dealer tommorrow, to get a full service history on the vehicle... I literally just got the thing last thursday, and I'm already over $100 in gas on it (got the thing on empty, $65 to fill it up and another $40 from half tank after driving 80 miles)...

The above poster is right, I'm going to force them to change the bumper now, the quick fix is already showing a break.
Oh ya well if it's under warranty then by all means send them back. Have them replace the bumper cover, and start telling them to check all the things I listed. Dealerships love when you tell them what to do
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Unread 12-27-2010, 07:48 AM   #11
JGCGEORGE
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Check your air filter as previously stated and make sure it is clean. Change your spark plugs and use the champion coppers. check your throttle body and make sure there isn't a bunch of gunk in it. If there is clean it following the procedure outlined elsewhere in this forum. make sure your intake tube and air box are clean. Air your tires to the proper psi. Make sure the oil in it is the appropriate 5w20. use seafoam in the tank and do the "sea foam treatment" via the vacuum line. Also, depending on miles over 45-50k, replace the egr valve. Hope some of this helps you and the wk jeeps page you were linked to earlier is really an awesome page and very informative.
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Unread 12-27-2010, 09:10 AM   #12
mavster
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So I think I'm just going to end up doing some of the MX...here's what I have planned

- Mobil 1 5w-20 Oil & M1-210 Filter (What's the recommended oil change rate? 6 months/5000 miles sound about right?)
- 16 x Champion 570s plugs
- The dealer said they changed the air filter, so I'll just double check it.
- I'm familar with the seafoam process, and I was always weary about throwing some in the tank...but should I introduce it into the vacuum line?
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Unread 12-27-2010, 05:43 PM   #13
Walt
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Quote:
Originally Posted by mavster View Post
...just picked up a ...2008 Jeep Grand Cherokee Overland edition.... including the hemi.......But I do have a major issue; something just isn't right with it.

My Fuel economy is in the toilet and I can't figure out why. I mean I have a hemi I know I'm not going to get 20mpg; but I do a mix between City (minor stops and go's between stop signs and lights to the nearest parkway or expressway) & Short highway bursts.

I'm struggling to get 10mpg, something just isn't right..and being new to the engine I have no idea where to start looking. I keep the mpg indicator active and notice when the "Fuel Saver" mode appears, but even then it's a leap to get 13mpg (doing anywhere between 40 to 60mph @ < 2k rpm on the tach).

So I was wondering if anyone had any tips?......
First of all: Welcome Aboard!

Didn't see where your MDS is -or- is not working.

In the RHS EVIC display, it will say FUEL SAVER when the MDS is active. Expect it to happen in low load condtions, above 24mph but below 70mph, engine coolant and oil temperatures near normal operating range, and transmission in D.

You should be getting ~14-15mpg around town and ~17-19mpg on the highway.

Have the dealer check for trouble codes (DTC) and do the HEMI driveability flash (see this TSB: http://www.wkjeeps.com/tsb/tsb_wk_1800610b.pdf ).

Things to check: Correct spark plugs (MOPAR or Champion 570's only), EGR valve operability, PCV valve operability, throttle body cleanliness (back side of butterfly), air filter element not plugged. These are the typical things that will inhibit MDS operability, and, thus, your mpg's.

Could be lots of other things, but start with the easy stuff first. As a matter of personal policy, I stayed with MOPAR parts until the 3/36 warranty expired. The dealer could never claim anything other than it was their/Chrysler's issue to solve. Makes life less complicated. You'll have plenty of time to wrench on it yourself later.
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Unread 12-27-2010, 06:38 PM   #14
mavster
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Quote:
Originally Posted by Walt View Post
First of all: Welcome Aboard!

Didn't see where your MDS is -or- is not working.

In the RHS EVIC display, it will say FUEL SAVER when the MDS is active. Expect it to happen in low load condtions, above 24mph but below 70mph, engine coolant and oil temperatures near normal operating range, and transmission in D.

You should be getting ~14-15mpg around town and ~17-19mpg on the highway.

Have the dealer check for trouble codes (DTC) and do the HEMI driveability flash (see this TSB: http://www.wkjeeps.com/tsb/tsb_wk_1800610b.pdf ).

Things to check: Correct spark plugs (MOPAR or Champion 570's only), EGR valve operability, PCV valve operability, throttle body cleanliness (back side of butterfly), air filter element not plugged. These are the typical things that will inhibit MDS operability, and, thus, your mpg's.

Could be lots of other things, but start with the easy stuff first. As a matter of personal policy, I stayed with MOPAR parts until the 3/36 warranty expired. The dealer could never claim anything other than it was their/Chrysler's issue to solve. Makes life less complicated. You'll have plenty of time to wrench on it yourself later.
- Yes I will confirm the "FUEL SAVER", display is shown.

Well since it's a CPO, i only have the 3 month/3k miles maximum care...

Heres the catch, I leave for oklahoma this friday...and if you havn't heard the NYC area is screwed with the blizzard...lol

So trying to get my truck in order, before I do a 1500 mile trip...

But thanks for the tips!
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Unread 12-27-2010, 07:24 PM   #15
90grandoneer
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Welcome, and congrats. on your new GCO. You're probably right, timely scheduled maintenance probably HAS NOT been done. Walt is right on, but he didn't mention (he usually does) to verify that the correct oil is installed. Dealers are notorious for putting the incorrect weight oil in the Hemi's. It must be 5W-20, preferably a good synthetic. Most of us using it go for 5-6K between changes. Tire pressure is another big mileage killer. I run my tire pressures at about 38 PSI. IMO, this gives (so far) the best tire life and driveability. Also check for abnormal tire wear. Improper alignment can also affect your mileage. I have all my vehicles aligned with the wife and I in the vehicle. This is its most common "on road" configuration. If aligned empty, alignment can change from in tolerance with no one in it, to out of tolerance when drivers/passengers are in it. If you keep the cruising RPM below 2000 RPM, you'll find you get better mileage. I normally run mine between 60-65 mph (~1800-1900 RPM), as I am no longer in a hurry. Above that the mileage/MDS operability decline rapidly. Good luck, and be safe on your trip. Let us know how the mileage checks out.

One other thing....if you're not using the roof rack, remove the two cross bars. Every little bit helps when it comes to wind drag.
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