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Unread 08-25-2008, 07:18 AM   #1
margotta78
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1980 CJ7 
 
Join Date: Aug 2008
Location: Tennessee
Posts: 74
Would like to increase GAS MILAGE

Ok I am going to be realistic about my 258 80 CJ7 and say I would like to get the most out of the Gas I pump in. I live in TN and where I am at no emissions test. Soo...what can I do to bumb that magic number up as high as let say...16mpg. I am not even sure what I get now because my gas gauge us broke. But I can assure you that when I ran out of gas the other day a block from my house I was pretty. I would also like to fix the gas gauge so I would at least know when to put more in. Now I am new at this stuff. I have put my 4" Suspension on, changed the radiator but when it comes to fuel lines, tanks, and emissions.

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Unread 08-25-2008, 07:25 AM   #2
HackFabrication
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1976 CJ5 
 
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Location: Canton, Michigan
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Need more info:
Transmission
Axle ratio
Tire size

I'll assume you're looking for a 'combined' city/highway MPG of 16 or better?

You can get a carb to run good. But it still won't compare in the driveabilty arena with EFI. Do some research on the 4.0L head/EFI swap.
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Unread 08-25-2008, 07:50 AM   #3
PavementPounder
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Quote:
Originally Posted by margotta78 View Post
I am not even sure what I get now because my gas gauge us broke.
Why do you need a fuel gauge to divide the miles you traveled by the number of gallons it took to fill up the Jeep?

If your 258 still makes good compression, the 4.0 swap is the way to go. If the motor is tired overall, swap in an entire 4.0 HO.
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Unread 08-25-2008, 10:44 AM   #4
JeepHammer
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1973 CJ5 
 
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Quote:
Originally Posted by margotta78 View Post
Ok I am going to be realistic about my 258 80 CJ7 and say I would like to get the most out of the Gas I pump in. I live in TN and where I am at no emissions test. Soo...what can I do to bumb that magic number up as high as let say...16mpg. I am not even sure what I get now because my gas gauge us broke. But I can assure you that when I ran out of gas the other day a block from my house I was pretty. I would also like to fix the gas gauge so I would at least know when to put more in. Now I am new at this stuff. I have put my 4" Suspension on, changed the radiator but when it comes to fuel lines, tanks, and emissions.
Don't need a gas gauge to tell mileage... Just an ACCURATE speedo with odometer that works, and you have to remember to write down the number of gallons and mileage on the odometer each time you fill up...

If you have oversize tires, the speedo is going to read slow, and that is going to show less miles for the tank full of fuel, so an ACCURATE SPEEDOMETER IS MANDATORY!

You CAN use an inaccurate speedo to tell if you are getting more, or less, mileage than before if you run a baseline before you do the service work...
-------------------------------------

I know none of you wants to hear this, but take the big stinky tires off and put on stock size tires for better fuel mileage!
This will put your engine back into the RPM range it was set up and designed for, and it will give your engine/drive train a better mechanical advantage on the road for take offs and acceleration...

With taller than stock tires, it's like having the 'Over Drive' turned on all the time! It's lugging the engine in RPM ranges the Engine wasn't tuned to 'Lug' in...
---------------------------------

Start with a full on 'Tune Up' & Full Service...
Service the differentials, check/pack the wheel bearings, service the transmission and T-case, Make sure the tires are aired up for highway use...

Get out the vacuum gauge and timing light, we gonna' party now!
Vacuum gauge will tell you if you are having problems with the engine,
http://www.junkyardgenius.com/tools/vacgauge.html

Using a long hose and leaving the vacuum gauge in the cockpit is a good idea. A vacuum gauge will teach you how to drive your vehicle for economy (and lonjevity!) if you pay attention to it!
The higher the vacuum reading, the better fuel economy you are getting.

Do a THROUGH inspection of your ignition system...
If you haven't done the 'TeamRush' upgrade yet, DO IT!
Getting the spark to the plug at the right time means better fuel economy!
If the plug doesn't fire, you get ZIP in that cylinder!

If you haven't looked into changing your ignition advance curve yet, I'd look into that too.
Bumping up the ignition curve, especially when you are in lower gears and stop and go driving, will help with fuel economy...
(Pulling a trailer or extending highway speeds in top gear... Not so much...)

MAKE SURE YOU DON'T HAVE VACUUM LEAKS!
Vacuum leaks, like when the button valve in the EGR gets cocked sideways, are hateful to the carb's efficiency!

If you have a carb that has seen better days, REBUILD IT!
Kit's are about $20 and can be done in an afternoon easily!
Drooling, Dripping, Leaking carbs are murder on fuel mileage...

Make sure you use the vacuum gauge and TUNE YOUR CARB!

I gained almost 3 mpg just servicing the drive train!
I would have stood on a stack of bibles and swore that 'Lube Is Lube' and should make a difference, but the calculator don't lie!
2.85 MPG average increase over 3 months after a full dive line service!

Guess fresh lube is more 'Slickery'!
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Unread 08-27-2008, 02:16 PM   #5
margotta78
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1980 CJ7 
 
Join Date: Aug 2008
Location: Tennessee
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well thanks that is a great start... The gas gauge would have helped from running out, because I have only had this CJ7 a short time.... finally got the 4" lift on... changed diff. fluids w/ Full Synth.. Then went to play a little. The only thing about using your odom. is if you hit the trail then thats all out the window. Thats what I did so we were creeping around rocks ect. So a working fuel gauge would let me know when its time to head home. I will have to invest in some spare gas tanks to mount w/ tire carrier. Currently I need a tire carrier. I will mess w/ it this weekend and see if I can get some clues.
I will also look into the EFI or a Weber carb I have heard good things about them.
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Unread 08-27-2008, 02:27 PM   #6
fayettenamvet
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Remember that the most effective (and cheapest) thing you can do to improve gas mileage is changing your driving manners. If you already drive like an old lady it won't help much, but if you have your foot buried in it all the time, you're not doing anything to help achieve your goal. Don't floor it at stop lights, don't wait until the last minute to stop at them. You don't need to always be doing 15 over on the highway. That sort of stuff.
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Unread 08-27-2008, 08:13 PM   #7
CJhollic
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1980 CJ7 
 
Join Date: Aug 2007
Location: Albuquerque, New Mexico
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I am getting around 18 mpg now. The most significant thing I did was drive around 2300 rpms which is 55 or so on my jeep. That got me about 2mpg over the 2600 I was diving on the highway.

The next thing I did was replace the carb with a Weber . That got another 1 mpg.

The Team Rush upgrade got me 1.5 to 2 mpg.

I have a T5 tranny (never use 5th), 33" tires, 3.31 gears.
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Unread 08-29-2008, 04:51 PM   #8
margotta78
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1980 CJ7 
 
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Location: Tennessee
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Yeah been talking to Jeep Hammer about the upgrade and I will do at ASAP. Then start with the carb adjustment. Now to the vacum lines. I bought a new PCV valve and I see it running to my carb but were is the ERG? I think the ERG takes the gas vapors that did not combust and pumps it back to the carb right? SO I guess I could just follow the yellow brick road. I have seen the filter canister that comes off the PCV but not the ERG valve. It should be on the manifold I think. The vacum system consists of what? The ERG I know but what does the vacuming? And yes the previous owners were dumb a##es. Nothing had been updated, renewed, and the wiring is well terrible. I guess they just figured if it didnt work they would just cut it. I have wires everywhere that are not connected. I just want to update and get rid of things I dont need to help gas milage.
Like team rush upgrade- adjust or replace carb, CDI module, do with an Electric fan and take off the belt driven ect.
Anyone know if 1980 CJ7 258 I6 has any smog control? I will get under and look for a Cat. converter. I have heard these will hurt milage.
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