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  #1  
Old 01-05-2013, 06:10 PM
martin.steve martin.steve is offline
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really bad fuel economy

hey everyone, ive got an 06 jeep commander limeted that ive bought used 2 weeks ago and its getting terrible fuel economy, (200 kms per tank) and there was a small amount of oil in the air filter. ive checked the pcv valve and changed the filter, and everything seems fine there, so im wondering, has anyone else had the same problem where the fuel consumption more then doubled, and what might cause this? any help would be awsome
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  #2  
Old 01-05-2013, 08:49 PM
06hemixk 06hemixk is offline
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I would do the usual run around especially if its the hemi. Can you post how many miles it has? Make sure the oil change is up to date with 5w20 if its the hemi. reset the ecu so it adapts to YOUR driving habits( You can do this by disconnecting the negative battery terminal and turning the key to the run position a couple times.) and not the previous owners. Make sure you use mid-grade. Regular fuel seemingly makes it angry when mpg's are concerned. I've noticed this with mine too.. For comparison im getting 14.4 mp average., on the 06 5.7 .
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Old 01-05-2013, 09:27 PM
martin.steve martin.steve is offline
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ive reset the stats when i bought it to factory so it would adjust to my driving but according to the computer monitoring system its saying im getting 21.9 ltrs per 100 kms which is crazy even for the hemi. mine is an 06 5.7 aswell, the last tank i went 203 kms on 70 ltrs so that about 112 miles on 18.4 gallons im thinking its got to be a sensor issue maybe MAF or O2 sensor, because the engine is running like a top so something is telling it to burn more fuel.im stumped, im thinking its diagnostic time, even tho im getting no check engine light. its got 205,000 miles on it now.
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Old 01-05-2013, 09:37 PM
06hemixk 06hemixk is offline
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205k miles? Congrats getting up there. With that many miles i would be thinking o2 sensor acting up as well. but still within range, hence no check engine light. Also the IAT would be a good thing to check, if the engine thinks the air is denser/colder than it actually is, it will dump fuel in.. Its gotta be running a little rich to burn like that.. What do you have for modifications? Btw i just did your conversion... comes out to 11.2 MPG.. But your second number stumps me, 6 MPg?? That is a little low. Whats the max you can achieve on the Highway?
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Old 01-06-2013, 12:35 AM
martin.steve martin.steve is offline
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no modifications at all bone stock, but at the end of the day only 200 km's out of a 70 ltr tank is just poor economy jeep or not. ive talked to other hemi owners who say they are getting 500- 550 per tank with stock hemi's so mine is less then half that, its BAD, really bad, im gonna take it in tommorow to a buddies shop for a diagnostic so hopefully that will yield some answers cause its costing a small fortune at 80 bucks per tank and only going 200 kms
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Old 01-06-2013, 08:09 AM
JBenn911 JBenn911 is offline
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He's got about 125,000 miles on it..probably time for a plug, filters and fluids change if the diagnostic doesn't turn anything up. 6.9 mpg even 11mpg is horrid... Most of my driving is around town, and with my lead foot, I average 12-13
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Old 01-06-2013, 11:37 AM
06hemixk 06hemixk is offline
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I hope he's done the plugs at least once at 125k Ben you think it could be a sensor acting up but still within parameters, hence no cel?
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Old 01-06-2013, 11:41 AM
JBenn911 JBenn911 is offline
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Being that its used, and with 125k on the clock, that would be my first order of business.. A sensor(like IAT, or MAF) could be off without throwing a CEL. Diddled around many a overly rich condition with my old Grand National, and often it was one of those two. I would think a shop manual or an all data type setup would have parameters for voltage on the sensors. Might help narrow down what it is or isn't...
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Old 01-06-2013, 11:52 AM
06hemixk 06hemixk is offline
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Alright Steve so it seems like you should check some sensors. I would check the IAT, O2, maf, Also the MAP and the coolant temp. ANy of these could make it run very rich, or possibly make it not go into closed loop. Open loop uses a lot of fuel. Your cat could also be taking a beating as a result of all the fuel. Ill try to find some parameters for those sensors so your buddy can test them. If he has access to a obd2 canbus scanner he can read all those sensors to see whats iffy.

Last edited by 06hemixk; 01-06-2013 at 11:59 AM.
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Old 01-06-2013, 01:43 PM
martin.steve martin.steve is offline
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so we just ran the obd scanner on it for the last 30 mins and we've discovered no codes, ive now unhooked the battery in an attempt to reset the system somewhat, but i have doubts that it will do anything, i guess now its time to find a hanes manual and get the parameers for those sensors and start testing. does anyone know if there is a place online where i can find the specs of my sensor systems?
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