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10-05-2009, 11:33 PM
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#1
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Registered User
Join Date: Sep 2005
Location: Lee's Summit, Missouri
Posts: 1,105
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Unreal. I had a coil go bad and so I also changed the plug on my 4.7 01. Fixed no problem. But also had a shop do an engine diagnostic to validate it was the coil. I went ahead and changed all the plugs.
After I fixed it I went to get gas... Filled up and reset the ave mpg and trip od. WOW. I got 75 miles on the first 1/8th tank. My computer also said I was averaging 18 mpg! I got to 100 miles on the first 3/8th's tank. THEN my mpg began to drop. By the time I got to 1/4 tank I was averaging 14 mpg and when empty I was showing 14 on the computer but the actual was about 12?
What gives? I have heard that the computer will adjust to changes like if you add a performance chip the ECM will adjust you back to original settings? How do I change the original settings in the ECM to get the better MPG I had with NEW PLUGS! (I also changed the PCV.) The exhaust does smell a bit rich!
Don't give me the lead foot routine either! I drove VERY easy and 80% hwy with easy starts, slow up the hills and coasted down trying to milk the entire tank!
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10-05-2009, 11:52 PM
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#2
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Registered User
Join Date: Mar 2009
Posts: 318
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I would run another few tanks & see what it brings. I never got good mileage out of the 4.7 I had in an 02 Dakota 4x4. 16MPG was the best if I drove 60 MPH on cruise & level road. If I had city or hills 14 MPG.
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10-05-2009, 11:55 PM
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#3
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Built and Supercharged 47
Join Date: Feb 2008
Location: Everett, Washington.
Posts: 1,942
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haha, im getting around 11-12 with new plugs, oil, filter, CAI, Exhaust, chip, 32" mud terrains, its a jeep thing.
__________________
Built Beater 01 WJ MY BUILD THREAD
Swapped, SUPERCHARGED Locked, Lifted and Long Armed.
02 Cummins. It has a smoking problem, And it wont quit.
K8 GSXR 1000- Racefit,Comp Werks,Puig,Woodcraft,B2 Industries,55W HID'S, R&G Engineering, Two brothers, ASV, DDM, "The pantie dropper"
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10-06-2009, 12:24 AM
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#4
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Registered User
Join Date: Sep 2005
Location: Lee's Summit, Missouri
Posts: 1,105
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Yea, my wifes WJ does 16-18 easy. I'm more like 10-12. But what really got me so ticked is I got good mileage right after the change. But I think the computer is screwing me by adjusting me down!
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10-06-2009, 01:46 AM
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#5
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Registered User
Join Date: Mar 2008
Location: park ridge
Posts: 1,085
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Quote:
Originally Posted by Airborne Lee
Yea, my wifes WJ does 16-18 easy. I'm more like 10-12. But what really got me so ticked is I got good mileage right after the change. But I think the computer is screwing me by adjusting me down!
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WHAT PLUGS ARE YOU USING?
did you rest the computer after the change? you should do it every time you put on a new electical part (take of neg cable) put foot on brake and turn the key all the way for about 30 seconds....
dont forget a new 02 is part of rutine tune up...
there are other things you can do to help milage of course things like new air filter, pump up the tires a bit.. change all the drive train fluids.
but there are cheap things like using dielectic grease at the end of the coils to the plugs, clean the throttle body and IAC, a lil seafoam can do wonders
oddly enough im one of the few people to get good milage out of the 4.7 in my sisters 04 wj
Q torque power gave me the best milage out of all the oils i have tired, and i prefur Lucas in my diffs cause it has low drag. i have gotten 435 miles out of one tank on a trip from chicago to NY set at 60 the whole time
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98 ZJ 3" lift homemade snorkel. JKS quicker disco 5.2L 150,000, 31x10.5 pro comp muds
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10-06-2009, 02:17 AM
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#6
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Registered User
Join Date: Dec 2001
Location: Denver, Colorado
Posts: 2,049
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Quote:
Originally Posted by jeepheller98
dont forget a new 02 is part of rutine tune up...
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Ummm? I don't think so. 
That tire on the top dosen't heelp things.
__________________
ZJ 98 5.9 LTD. Lots of mods. 7" T&T's Long Arm Lift ,BFG KM2"s,35X12.50x16's,4:56's, Vanco brake upgrade, M1intake,Holley52mmTB,MikeLeach Headers,, Arb'ed HP D30,Aussie Locked rear,Procomp MX6 Shocks,Arb front,RearTR bumpers,ECT.ECT.
Latest Pics
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10-06-2009, 05:12 AM
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#7
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Registered User
Join Date: Aug 2007
Location: Knoxville, TN
Posts: 2,302
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Quote:
Originally Posted by Airborne Lee
After I fixed it I went to get gas... Filled up and reset the ave mpg and trip od. WOW.
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This is why it went up. Anytime I reset the overhead in my Jeep it starts off showing this great mileage and then "catches up" to reality by the end. I think they rigged it for test drives 
You're driving a V8 SUV plus a big windblock on the top - I doubt you'll ever see 18 mpg consistently.
__________________
2004 4.0 Selec-Trac
BB->Black Diamonds->General Grabbers
Quote:
Originally Posted by Sporer65
You need to learn, there are 3 things that all JF members must like beside Jeeps:
(1) Guns (2) Women (3) Bacon
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Quote:
Originally Posted by GraKee99
I was bored so I forded the river. No oxen were lost.
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10-06-2009, 06:40 AM
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#8
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2000 Laredo V8
Join Date: Oct 2003
Location: Raleigh, NC
Posts: 2,855
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Yep...I'm not even sure what some of it is such as "sienna" and M416 but I'm pretty sure you're not going to get back to published MPGs with that on.
"Sienna, 2.5" BB, AT/KO 31", Westin Nerfs, Yakima Rack, KC lights, M416
I see that you have 2 WJs? We're talking about the more modded one, right?
__________________
2000 Laredo 4.7L Selec-Trac. 161K miles, Leather, 245 tires, tow package, crappy CD changer, full size spare, roof cross-rails & sunroof.
Changes & fixes: Rear Addco sway bar & greasble bushings, upgraded headlights, upgraded tail lights, new hood struts (replaced 2X), new rear hatchglass struts, new radiator (replaced 3X), new oil pressure sending unit (replaced 2X), 2 new speed sensors, 2 new door lock actuators, new ignition key cylinder, chrome front tow hooks, Mobil 1 Synthetic 5/30, Purolator Pure One oil filter, EBC slotted & dimpled rotors, EBC Greenstuff pads, new front shocks (replaced 3X), new rear shocks (replaced 2X),
new IRO steering stabilizer, new timing chain cover, new water pump, thermostat, new thermostat housing, new high pressure power steering hose, Michelin-X radials, new sunroof assembly, new single-piece lug nuts, new exhaust manifold studs & gasket on driver's side. Jeepforum.com sticker, Visit cobaltboatsforum.com when you can!
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10-08-2009, 09:52 AM
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#9
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Registered User
Join Date: Sep 2005
Location: Lee's Summit, Missouri
Posts: 1,105
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The picture with the tire on top was taken when wheeling. I don't keep it up there. I'm sure I'm loosing 1-2 mpg with the rack maybe a bit for the 31" tires but on the hwy i'm still getting 12 mpg average based on actual miles/fillup. ALL of the normal maint. items are in great shape and new, clean and correct. my old engine blew at 90k miles and my jasper reman (long block) gets the same mpg. this is not a maint issue. There is a programming or trainy issue. Getting 18 mpg after the last tune up clearly indicates that SOMETHING is out of wack. (Sorry for the technical terms)
I'm really ticked about this because my wifes WJ 6 months newer get 17-18 mpg on the original engine with 130k miles.
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10-08-2009, 10:38 AM
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#10
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Member
Join Date: Sep 2009
Location: St. Paul, MN
Posts: 421
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Just throwing this out there, but if you haven't recalibrated your speedo since upgrading your tires, your tripometer is probably lying to you.
What were you averaging before the tune up?
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10-08-2009, 10:39 AM
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#11
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Member
Join Date: Sep 2009
Location: St. Paul, MN
Posts: 421
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Quote:
Originally Posted by solomon8718
Just throwing this out there, but if you haven't recalibrated your speedo since upgrading your tires, your tripometer is probably lying to you.
What were you averaging before the tune up?
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... Assuming you're using your tripometer to figure out your actual miles...
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10-08-2009, 10:39 AM
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#12
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Registered User
Join Date: May 2008
Location: Marquette, Michigan
Posts: 1,304
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WJ speedo is pretty much true with 31" tires.
__________________
|94 XJ|4.0|NP231|AW4|8.25 Trac Lock|Lotsa miles - SOLD
|99 WJ|4.7|242HD|Vari-lok|Upcountry+BB|DT8000|Dead as of 10/29/2009
If it aint broke, fix it till it is.
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10-08-2009, 10:46 AM
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#13
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Member
Join Date: Sep 2009
Location: St. Paul, MN
Posts: 421
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Quote:
Originally Posted by 99avant
WJ speedo is pretty much true with 31" tires.
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hmm... interesting. Is there a non-stock size that is true for the zj as well? That would be ideal for me since then I wouldn't have to mess with the stupid gear in my tc. Sorry, don't mean to hijack the thread.
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10-08-2009, 10:53 AM
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#14
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Registered User
Join Date: Aug 2005
Location: Memphis, TN
Posts: 2,866
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Maybe you have already taken this into account, but with 31" tires instead of the stock 29", your speedometer will read about 7% low and so will your odometer. That makes odometer miles divided by gallons lower than it actually is, because of the odometer error. The VIC mpg reading will be lower for the same reason. The error would account for about 1 mpg of the apparent mileage loss. The rolling resistance and inertia of the larger tires could easily cost you an actual loss of 1 mpg also.
Oops, I see solomon 8718 beat me to some of this.
99avant, that can't be true in general because my 01 and the wife's 04 have 29" tires and have correct readings.
__________________
2001 WJ Limited with Quadra-Drive, Kenne Bell Supercharger, 3-inch Kolak exhaust, Stillen rotors (F/R) and MM pads, Addco sway bars (F/R).
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10-08-2009, 10:54 AM
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#15
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Registered User
Join Date: Sep 2005
Location: Lee's Summit, Missouri
Posts: 1,105
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Driving to CO then to WI nearly 4000 miles my speedo was only a few miles off.
the actual miles after the plug/coil/PVC change really was nearly 5mpg better but by half tank it was back to 10-12 again.
This is not a tire pressure air filter kind of issue.
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Wasted TuneUp
