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Discussion Starter · #1 ·
My 88 wrangler gets the worst gas mileage. It is mostly stock with the exception of a pacesetter header, weber carb (with adjustable fuel pressure regulator), and tires about 30" in diameter. Last time I got gas it was only getting 10 mpg. It seems like it used to get better mileage, but I don't know. It also seems like if I drive a certain speed, like around 55-60 mph, that you can almost see the gas gauge go down. At first I thought it was the gauge, but not since I calculated my mileage to be only 10 mpg. The Jeep has about 110,000 miles on it. Is it just the nature of an old Jeep, or can I fix it? By the way, the Jeep has stock axles and ratio and a 6 cylinder w/ a 5 speed. Help!!
Dan


 

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On a recent road trip with my 90 YJ, I averaged around 18 mpg highway. The last time I checked city mpg it was around 13 mpg, but this was before a K&N filter and Borla cat-back. From what I read, my milage is about average. I've got the Carter BBD, 3.07 gears and 225/75R15 tires.

jerry
 
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Discussion Starter · #3 ·
My 87yj with 258 I6 35in mts and 4.10 gears avgs about 13 mpg combined city/hw driving. I've just completed the first part of the TEAMRUSH ignition upgrade(cap,rotor and wires) and I can see some improvement in milage after 1/2 tank of gas.After I add the tfi coil I'll check the milage and post it. rh

 
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Discussion Starter · #4 ·
somethings wrong. my stock 87yj gets 20 mpg. 6cyl 5spd with stock carter. did you put on the weber? did it ever get good milage for you?
steve

 

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mine was ranging from 8 to 12. since the pro-jection i think it's gone down. but the drivability is better. i'm working on a write up on it too since i have had a few emails about it.

79/CJ-7/AMC360/TH400/Q-TRAC/d30/d44/33's/RS9000s/Herculiner/Pro-jection 2D
 
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Discussion Starter · #6 ·
When my yj was stock with 3.07 gears,215 tires and the carter carb in perfect tune I avg around 18 combined city/hw.The key word here is"carter in perfect tune" something that only occurred after yearly trips to my mechanic.When I put on the Weber,it started easier,never stalled at stoplights and I had much more power.I did notice a slight drop-off in mileage down to a steady 17 in combined driving.The drop to 13 only happened after adding 35's,4.10 gears and 6 inches of lift and a rear locker.I've been told 13 is avg. with this combo of tires,lift and gears.I've also been told that adding a regulator would help the Weber perform better so that is my next addition rh







 

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/wwwthreads_images/icons/tongue.gif If you look at fuel consumption curves developed from the factory test data, you will notice that fuel consumption (Gal/Hr/Hp) is optimum at a fairly narrow RPM range. Above that range, intake losses and piston speed affect it, and below that the four-stroke cycle just cannot make good use of the exhaust flow for scavenging, and the best carb CFM for good venturi action. If you change tires, you need to figure out how many TURNS PER MILE you were running the driveline originally, and get back to that number by a gear swap. To figure it get the TURNS PER MILE of the old tires(the tire shop has this in the book) and then multiply by the axle ratio to get DRIVELINE TURNS PER MILE AT 60. By using driveline turns per mile at 60, you can divide by various ratios till you get the TURNS PER MILE OF THE BIG TIRES that the dealer book said they were. So....Turns Per Mile(little tires)X Original Gear Ratio = Turns Per Mile (big tires) X New Gear Ratio. You can see from that equation that as turns per mile go DOWN that axle ratio MUST GO UP. The engine DOESN'T CARE what tires you run or what gears you have....all it knows is that it wants a CERTAIN NUMBER of driveline turns per mile to propell the Jeep at 60 MPH and get good fuel useage numbers./wwwthreads_images/icons/smile.gif

CJDave
Quadra-Trac modified by the crack moonguy/wwwthreads_images/icons/wink.gif/wwwthreads_images/icons/smile.gif/wwwthreads_images/icons/tongue.gif transfer case team.
 
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Discussion Starter · #8 ·
My engine may not care what tire size I have or what gears but it does feel all that extra weight and the added wind resistance of a big lift and mud tires vs at tires.Also with the gear change I have around 10% more power so I'm turning more rpm's at 60 mph.Btw with the TR ignition upgrade my mileage has improved from around 13 to almost 15,and this is with just the cap,rotor and wires.If the TFI coil helps mileage any I will be getting better mileage than any of the people around here with 4wd trucks that use them the way I do my jeep.Question,will the TFI coil help mileage

 

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/wwwthreads_images/icons/tongue.gif What you'll need to do is set up the fuel tank with a drain. Your gas mileage will be SO GOOD that you'll have to stop periodically and drain out fuel to keep from running the tank over./wwwthreads_images/icons/crazy.gif

CJDave
Quadra-Trac modified by the crack moonguy/wwwthreads_images/icons/wink.gif/wwwthreads_images/icons/smile.gif/wwwthreads_images/icons/tongue.gif transfer case team.
 
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Discussion Starter · #10 ·
Gas milage what gas milage this is my second jeep my first was an 81 cj5 with a 258 it got about 15 mpg average when the 6 cyl dided i put in a 304 it averaged about 10mph when that motor dided the wife said buy a newer jeep the old 5 is to small so i upgraded to an 82 cj7 not quite what the wife ment by newer but its bigger anyway it's average is about 15mph i just finished the TeamRush upgrade with cap wires TFI and MSD 6A and i cant beleave the difference idles smooth down to 500 RPM and has more power just from a seat of the pants fealing don't know about milage since the upgrade since i can't keep my foot out of it yet. But even with gas in the low $1.90's i would not trade this ride for any other%
 
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Discussion Starter · #11 ·
When you put on the larger tires you did recalibrate your speedometer/odometer? Your mileage calculations could be off 20% or more if you didn't. Also check that the choke is fully opening and that the air/fuel ratios are correct, this may mean a trip to the tune-up shop. Your YJ should be getting around 15mpg, at least, if you're not much heavier than stock.

 

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When I rehooked the 4wd and some vacuum hoses to where they were supposed to be, mine increased from about 10 to 15mpg. Not sure how it happened but it did.
Make sure your timing is good, hoses aren't clogged, invest in a K&N air filter, and the TFI upgrade.
PS. All of this may keep your foot from having to be so heavy, saving you some gas. Working for me, but I still have to get the TFI on there.
Bryan/wwwthreads_images/icons/crazy.gif
 
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Discussion Starter · #13 ·
My jeep is used like a farm truck.I haul around 500 lbs of feed along with 8 sguare bales of hay or 1round bale on a trailer 13 miles to the farm.I also spend a lot of time idling while opening gates and loading feed,hay etc.Also after the gear/tire change I did not correct the speedo.It is off about 10%.Even at 13 mpg I am still getting better mileage than the Dodge and Ford 4wd pu's my co-workers drive for the same type of work.The Chevy still gets a little better mileage than any of us but I can still have a lot more fun after work than they can and they always want to go with me. rh

 
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