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Old 06-25-2014, 09:59 PM   #1
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mpg dropped dramatically

My 2010 jk was getting average 19-21 mpg on Highway. Now I've been getting an average of 13 - 14 mpg on Highway. I have a k&n cold air intake (which I have to clean) . Other than that, the jeep is basically stock. I know I need a tune up, That I plan on doing this week. I already replaced my fluids with royal purple bout 4 months ago. Any other ideas? Should I just go with basically stock grade plugs and wires?

Thanks!!

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Old 06-25-2014, 10:03 PM   #2
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Any codes ?

I can't see a drop like that just being a tune up, has it been getting worse over time or just suddenly dropped ?

Could be a lot of things.

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Old 06-25-2014, 10:05 PM   #3
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Checked tire pressure lately?
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Old 06-25-2014, 10:08 PM   #4
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I had an identical change when I moved to Houston Texas from Utah. My wife's Toyota Camry hybrid had a similar percentage drop in efficiency as well so I assume cars dislike the hot and humid weather as much as I do. I have monitored mine for the last 2-3 years and it seems to fluctuate with the season some (not to the extreme moving to Houston caused) but I did get improvement after doing a tune up around 50,000 (I was surprised how bad the spark plugs had eroded in such a short time).
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Old 06-25-2014, 10:10 PM   #5
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That's pretty dramatic. Are you tracking manually or is that what the Jeep is telling you? What kind of gas are you purchasing? The higher the ethanol value the worse your mileage will be. How's the tread and air pressure in your tires? Run with a little more air pressure to see if you gain anything back. You might have something going on with your computer too. The really bad part is could be a number of things. Let the process if elimination process begin. Good luck!
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Old 06-25-2014, 10:23 PM   #6
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Are you running topless or doorless? Also, wind blowing the wrong way can be a serious detriment.
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Old 06-25-2014, 10:32 PM   #7
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Thanks for all the replies so quickly. Where to begin, I have about 50k on the engine. I just rotated the tires and only went crawling once since I got them since bout 18k ago. Pressure is about 32 on the tires. I got a botched job when I replaced my clutch and fluids with this guy. He also did a new battery and oilchange. And that's when everything started going down hill. I'm gonna bring it to jeep to just see if they can run the computer on it and see if anything wrong. I'm getting a shake too, and I brought it to my local truck guy and he said before I start going crazy and thinking the worse. CLEAN THE ENGINE, and do a basic tune up cause that might help out. And my computer may need to be updated.. So if any of that helps
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Old 06-25-2014, 10:35 PM   #8
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Oh and I put regular gas, nothin to do with doors off or top less. When I was driving to raush in PA from Westchester NY before all this happened I was getting around 20 highest was 23 mpg right after I did the cold air intake. Now just going bout 96 miles to my girls, it's bout 13.9 mpg. Smh, I honestly don't even enjoy driving my jeep anymore. This guy was like the cancer of my jk
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Old 06-25-2014, 10:47 PM   #9
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This could be a myriad of possible issues or a combination of them. Hopefully Jeep can figure out what is going on, but it seems like it could definitely be related to the recent work you had done. The shaking doesn't sound normal, especially with fluid changes and tire rotation. Make sure they check fluids, properly torque the tires, and check them for uneven wear. It wouldn't hurt to make sure the suspension is properly torqued and nothing was knocked loose or damaged by the mechanic you used recently.
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Old 06-26-2014, 06:36 AM   #10
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The shaking could be caused by the tires needing to be balanced.
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Old 06-26-2014, 11:42 AM   #11
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I would start out by looking at the plugs - making sure they are at the right gap, right part number and general condition.

Then do all the general maintenance over again - new oil change, air filter, etc.

Maybe check your O2 sensor - could just be coincidence and you could be running rich and not know it.
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Old 06-26-2014, 11:53 AM   #12
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When you say shaking do you mean more of a shudder? You mentioned you had a botched install on a clutch, did it get fixed correctly? That sounds to me like the culprit.
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Old 06-26-2014, 03:11 PM   #13
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I'm gonna bring it to jeep to out it on the comp to check out. The shaking was with 2 things, 1 was almost like when idling at a light or something the engine would shake a lot more than norm and sometimes feel like it was gonna stal out. ( I'm thinking that more of the tune up if anything) the other shaking was the front passenger side tire area. First noticed it while doing like 80 on the highway, actually felt like the start of a flat tire. The light thud thud thud* sound. So I rotated the tires thinking maybe it was from the tread of the Rubicon style mud tire. It's been alil better.
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Old 06-26-2014, 03:46 PM   #14
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not trying to scare you but with my last jeep (99 WJ) I had a similar thing happen and the head had cracked. might want to see if your oil and coolant are mixing. Mine had substantially more mile but its something you might want to check sooner rather than later
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Old 06-26-2014, 04:30 PM   #15
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Quote:
Originally Posted by Hokieneer View Post
not trying to scare you but with my last jeep (99 WJ) I had a similar thing happen and the head had cracked. might want to see if your oil and coolant are mixing. Mine had substantially more mile but its something you might want to check sooner rather than later

I 2nd this.....But mine ended up being the intake manifold gaskets on an 07............any leaking fluids or running hot?
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Old 06-26-2014, 05:04 PM   #16
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I have been getting 18 - 19 plus. The other day I pulled over to take a phone call and send a couple text msgs, probably 10 minutes idling with the air blasting and when I got to my appt early I idled again for another 15 to 20 minutes. When I check my MPG I was down to 14 mpg. I had no idea idling would ding the mpg that much. Now a few days later my MPG is slowly heading north. I think with the warmer weather maybe we all are idling a little more with the air on then we did a few weeks ago?
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Old 06-26-2014, 05:13 PM   #17
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Originally Posted by schirmyver View Post
Maybe check your O2 sensor - could just be coincidence and you could be running rich and not know it.
Exactly what I was going to say. I've had more than one bad O2 sensor in my lifetime, and they do affect gas mileage.
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Old 06-27-2014, 09:49 AM   #18
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Quote:
Originally Posted by HydroWilly View Post
When you say shaking do you mean more of a shudder? You mentioned you had a botched install on a clutch, did it get fixed correctly? That sounds to me like the culprit.
I agree with this. If your mechanic put in a cheap made in China clutch with low quality friction material you would experience clutch slip and shudder resulting in poor mpg.

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