manche Posted September 21, 2008 Share Posted September 21, 2008 hi i got a 89 jeep comanche sportruck with stock susp. 23s 2.5l and I'm getting only 14mpg i have replaced the cat, distributer cap ,new o2 sensor ,new plugs ,new air filter, and new fuel pump i should be getting around 20mpg any ideas wats wrong Link to comment Share on other sites More sharing options...
Wildman Posted September 21, 2008 Share Posted September 21, 2008 It's got to be the roll bar causing wind drag........... :teehee: That's hard to believe, cause my first MJ 6+ years ago was a stock, 2wd, 2.5, 5 speed, and I was pushing 20-22 mpg :hmm: You went thru all the items that you should, but, did you check if the brakes are dragging?, are the axles in good shape, IE: the bearings lubed and working correctly? Are you running stock tires?? Like 215/75R15's and the proper air pressures? And in previous treads........how are you calculating the mileage? Link to comment Share on other sites More sharing options...
mvusse Posted September 21, 2008 Share Posted September 21, 2008 When you replace the distributor cap you should ALWAYS also replace the rotor. When you replace the cap and the plugs, it only makes sense to also replace the wires. Also, make sure your odometer is correct. Either check is against a measured 10 miles you can find along the road in some areas (a measured 10 miles against a 1/10 mile odometer will tell you how far off you are to 1%) or check against a GPS. The odometer and speedometer run of the same cable. If one is off either from running the wrongs size tire, regearing the axle or replacing the speedo gear with the wrong one, the other will be off by the same fraction. And as Wildman asked, how are you calculating your mpg? The only accurate way is to always fill your tank to full, where the pump shuts off (but don't try to top it off, as that gas will only end up coming out of the vents on top and hopefully in your charcoal cannister, if it and it's lines are still there and operating), let it go down to 1/4 or 1/2 tank before filling and averaging that number for 3 or more fill ups. Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 I'm calculating 16gal divided by milage between fill ups so if i had example if i had 3 gallons of gas and 214,142 and when its empty there is 214,184 on odometer i then minius the difference so 184-142=42 then divide it by 3gal 42/ 3=14mpg by the way is in reference on the breaks I'm wondering also is my e-brake wire snaped at the stud is it possible that my rear drums are still rubbing? Link to comment Share on other sites More sharing options...
FxRacing282 Posted September 21, 2008 Share Posted September 21, 2008 are you a spirited driver? i know when i drive fun i get like 4mpg in my truck. then i drove like a granny and got 32mpg in my corolla as opposed to driving spirited in it and getting about 15. Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 well i drive 50-55mph in city and about 65-70mph on hwy Link to comment Share on other sites More sharing options...
FxRacing282 Posted September 21, 2008 Share Posted September 21, 2008 nock it down 15 mph and see what your getting Link to comment Share on other sites More sharing options...
aemsee Posted September 21, 2008 Share Posted September 21, 2008 not really related to your fuel thing, but what are 23 tires? Link to comment Share on other sites More sharing options...
FxRacing282 Posted September 21, 2008 Share Posted September 21, 2008 not really related to your fuel thing, but what are 23 tires?\\ heh heh good question Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 those are 23s Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 Link to comment Share on other sites More sharing options...
aemsee Posted September 21, 2008 Share Posted September 21, 2008 Hmm...still don't get it. 23 as in 23x7x15? That would be a damn short tire. What am I missing here? Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 23x7.5x15 Link to comment Share on other sites More sharing options...
Eagle Posted September 21, 2008 Share Posted September 21, 2008 by the way is in reference on the breaks I'm wondering also is my e-brake wire snaped at the stud is it possible that my rear drums are still rubbing? It's not only possible, it is probable. 23x7.5x15 Is that what's listed on the sidewall as the tire size? I never heard of that size. A stock 2.5L MJ should probably have had 205/75R15 or 215/75R15 tires. Either of those would be quite a bit larger than a 23" tire. If you are running a tire that small with the stock speedometer gear, you are not really traveling as far as your odometer says you are traveling. Which would make your real-world gas mileage WORSE, not better. Check those brakes. Link to comment Share on other sites More sharing options...
WyoCherokee Posted September 21, 2008 Share Posted September 21, 2008 what gears do you have? I'm running the 3.55's with my 2.5 and 4speed and i average 25-27 mpg at 70 on the highway. hows the air filter? fuel filter?. and those tires seem pretty short. might try some lt215/75's Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 ok correction they are 223x7.5x15 Link to comment Share on other sites More sharing options...
aemsee Posted September 21, 2008 Share Posted September 21, 2008 Is that a recap tire? Link to comment Share on other sites More sharing options...
aemsee Posted September 21, 2008 Share Posted September 21, 2008 ok correction they are 223x7.5x15 Look closer, probably 225/75/15. If it was originally equipped with 205's, then you are traveling a bit further than the odometer is showing. (also traveling faster than the speedo is showing). Link to comment Share on other sites More sharing options...
fiatslug87 Posted September 21, 2008 Share Posted September 21, 2008 A stock 2.5L MJ should probably have had 205/75R15 or 215/75R15 tires. My '90 Sportruck with a 4.0L came stock with P195/75/15 tires :oops:, I bought it new so I'm certain of this. It's even on the window sticker. However, this was on a 2WD. Link to comment Share on other sites More sharing options...
FxRacing282 Posted September 21, 2008 Share Posted September 21, 2008 ok correction they are 223x7.5x15 Look closer, probably 225/75/15. If it was originally equipped with 205's, then you are traveling a bit further than the odometer is showing. (also traveling faster than the speedo is showing). thats true but its not going to affect the outcome much. maybe 1mpg. a 205/75r15 is not much smaller than a 215/75r15 Link to comment Share on other sites More sharing options...
BLHTAZ Posted September 21, 2008 Share Posted September 21, 2008 So he has roughly a 28" tall tire based on what I see. A 225 is just slightly over 28" tall. As for MPG calculations...it is as simple as fill up the truck, note the mileage, drive it through at least half the tank full, fill it again and note the mileage again. Subtract your first fill up mileage from the second and divide that by the gallons used. 200 miles traveled - divided by - 10 gallons = 20 mpg Link to comment Share on other sites More sharing options...
Eagle Posted September 21, 2008 Share Posted September 21, 2008 Looking at some tire data I compiled awhile ago, a 195/75R15 was rated at 760.7 revolutions per mile. A 225/75R15 was rated at 713.1 revolutions per mile. That's a difference of 6.26 percent, which is how much the speedometer and odometer will be off (assuming they were somewhat accurate with the stock tires). If we apply that to a calculated fuel consumption of 14 MPG, the corrected figure comes out to 14.8 MPG. Still quite a bit short of what it should be. Link to comment Share on other sites More sharing options...
manche Posted September 21, 2008 Author Share Posted September 21, 2008 ok here antidisestablishmentarianism i read off tire is a 235x75xr15 Link to comment Share on other sites More sharing options...
Eagle Posted September 21, 2008 Share Posted September 21, 2008 You're still not reading it correctly. It's 235/75R15. These sites may help you understand the numbers better: http://www.car-videos.net/info/tirespecs.asp http://www.buicks.net/shop/reference/tires.html http://www.wheelmax.com/Tire-Size-Descr ... icle34.asp Link to comment Share on other sites More sharing options...
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