Jeep Commander Forum banner

really bad fuel economy

20K views 37 replies 7 participants last post by  Centcomm87 
#1 ·
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
 
#2 ·
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 .
 
#3 ·
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.
 
#4 ·
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?
 
#5 ·
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
 
#6 ·
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
 
#7 ·
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?
 
#8 ·
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...
 
#9 · (Edited)
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.
 
#10 ·
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?
 
#11 · (Edited)
Ive been looking online trying to find the resistance numbers... do you have a scanguage or any type of obd2 interface that lets you read real time parameters.. I have a scanguage lets me see the iat, map, coolant temp and 02 sensor reading. It would help to read those while your driving. Maybe you could borrow a friends ? ALso just remembered the EGR valve has a lot to do with mds kicking in and poor economy.
 
#12 ·
When the engine is hot it should read in the range of 2-2.5k ohms(k=1000). While cold it should read about 6k ohms. Thats for the IAT... For the coolant sensor The resistance across it is about 13,000 ohms with engine off at room temperature. With engine fully warm, it is 600 to 1,000 ohms..... Still looking for the others.. If i had to pick two sensors to change .. I would pick 02 and the MAp.. From what ive heard those two do the most damage to mpg if faulty..
 
#13 ·
so ive been driving it around with nothing running not even the heat, and ive discovered that it is (maybe) misfiring or lagging around 60kms/hr the part i really dont understand about any of it is that if theres a bad sensor, or a misfiring cylender then it SHOULD throw a code. its so frustrating. im about ready to break down and take it to the garage. i just dont want to pay
 
#14 ·
the misfire could be cause by a rich mixture or bad plugs.. It should throw a cel.. Are you sure your not feeling the Mds kick in? At 37mph(60kmh) in mine i can usually get it to drop into final gear and mds kicks in, hence it feels like its bogging because its below 1500 rpm. which might be what your feeling. If you wanna see if its that then put it at tow haul mode and see if you can repeat the issue. Tow Haul mode will not help your mileage at all though cause it will turn mds off. It might be a fluctuating or combination of Off sensors that make it run rich.. They can be Off the norm but still within parameters of the ecu so no CEL.
 
#15 ·
its starting to look like the o2 sensors or faulty plugs, its going in tommorow hopefully to have the obd2 scanner put on it while its driving for a diagnostic, its crappy to have to pay for the diagnostic but i see it as the most streamlined option for finding the issue, so here goes 85 bones lol. ill keep everyone posted on the discoveries in case this happens to you.
 
#16 ·
Alright Good luck sir. You should look into a scanguage. I love mine. PLus it reads and clears DTC.
 
#17 · (Edited)
You might add the LED to tell when MDS is kicking in or not. See this thread http://www.jeepcommander.com/forums/showthread.php?t=10433
For the LED part see Page 5 starting with post 45, http://www.jeepcommander.com/forums/showthread.php?t=10433&page=5
I didn't remove the dash or anything difficult, just popped down the door under the steering wheel and ran the wires there and set the LED on the dash below the instruments in a little box with a switch in it also.
I have had mine running since that post with no problems.
 
#18 ·
so after taking it to two different shops, having them run obd2 while idleing, standing still, while driving, and having them probe it to check the gas levels of the exhaust, i have yielded no results. no mechanic of the three ive now seen total, has any idea what is causeing it to be so terrible on fuel, the best answer ive gotten is that maybe the fuel gauge is malfunctioning, so the advice ive gotten is to fill it as much as i can, drive 100 kms and then fill it again and see how much that cost me. I dont need to do that tho because i just forced 29.68 litres of fuel into it and checked the trip which read 84.2 kms, do some simple math and ive come to the conclustion that its getting these numbers 6.67 MPG or 35.25L/100kms which costs me 66 cents per mile or 41 cents per km, thats really bad math no matter wheather the fuel gauge says empty or full. im at my wits end, i cant see changing a spark plug or a tune up fixing mileage that bad? my next question is does anyone know how big the fuel tank is in the 06 commander limeted hemi?
 
#26 · (Edited)
For some added info, there are two codes that are thrown if the Hemi is stuck in open loop:

P1129-CLOSED LOOP FUELING NOT ACHIEVED - BANK 2
P1128 - CLOSED LOOP FUELING NOT ACHIEVED - BANK 1

Enable conditions are met and the 02 sensor has not been in closed loop control at least once on each of the two consecutive trips, the MIL illuminates and the DTC is set. Two Trip Fault. Three good trips to turn off the MIL


... having them probe it to check the gas levels of the exhaust, i have yielded no results.
Do you trust them on this? Pretty sure this would mean that you HAVE to have a fuel leak somewhere. 16L/100km more than my Hemi is burning, can't see how it could burn it and not be running rich. (for reference I am usually around 17-18l/100km)


...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 i
12.6l/100km difference between the the ecm's calculations and actual. Maybe another indication of a leak. Do you get further on a tank if the Jeep sits less?
 
#20 ·
well, im thinking im gonna try to get ahlod of the hemi manufacturing plant, cause if anyone knows what could cause this without tripping a code it would be them... any chance anyone knows what their number is? sounds like a joke but everyone i know is stumped including people ive paid to figure it out.
 
#22 ·
i sent an email to both of those contacts and they both got back to me, they took my vin and home phone number and are submitting a work ticket to investigate the problem, so with any luck ( fingers crossed) they will get back to me with some sort of answer. thanks 06hemixk, youve been so helpful so far!
 
#23 ·
Not a problem Martin. Hopefully that will get you further than contacting the dealer and having them charge you for silly diagnostics. Plus they have a lot more "pull" being in corporate if you do need some work done. :rolleyes:
 
#24 ·
well yeah cause really i kinda feel like now its at the point where it should not be my dollar spent to solve the problem since diagnostics and trusting the mechanics to figure it out hasnt worked, not to blame the mechanics at all just sayin , if they cant figure it out then what else can a person do ?
 
#25 · (Edited)
Wow that is horrid efficiency. Hope you can diagnose it soon.
It is odd that you are not getting any codes thrown with such crappy mileage. I assume someone has checked for fuel leaks? A compression check would be a good place to start as well just to rule out the mechanics of the engine. Also, like was said a full tune up is in order. Doubt new plugs fluids will fix the problem but it swill help a bit and should be done anyway.
 
#27 ·
Pleas don't laugh too much, but... Have you verified that your speedo, or more importantly odometer are reading right ?? I know wheel and tire change will throw your odometer and mpg readings off, not to the degree you have, but it could be one more thing to look at :)
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top