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Unread 07-31-2013, 06:57 AM   #1
richtfan
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need help with fuel economy

90 yj 4.2 with the carter bbd carb.
5 sp manual tranny
tires are 30-950r15

i need to try to increase my gas mileage however I can.

The carb seems to run fine. I don't think there are any vacuum leaks.

it sounds as if it lopes a little, but that might be the exhaust.

any suggestions?

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Unread 07-31-2013, 08:21 AM   #2
fourbtgait
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Quote:
Originally Posted by richtfan
90 yj 4.2 with the carter bbd carb.
5 sp manual tranny
tires are 30-950r15

i need to try to increase my gas mileage however I can.

The carb seems to run fine. I don't think there are any vacuum leaks.

it sounds as if it lopes a little, but that might be the exhaust.

any suggestions?
What is your gas mileage?
What is your axle ratios?

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Unread 07-31-2013, 08:49 AM   #3
richtfan
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i don't know the gear ratios other than to say that they are stock.

gas mileage the other day on the highway (hard top removed) was about 12-13 mpg.
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Unread 07-31-2013, 09:02 AM   #4
jokerchief462
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It's a little low. With the too removed you will see a small decrease in mpg.

A good tune up, tires at recommended psi and a good wheel alignment should be 15 mpg or more depends on how you drive also.
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Unread 07-31-2013, 09:06 AM   #5
Old4X
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Tell us how your engine is tuned and what shape it is in:

Compression?
Vacuum reading at warm idle?
Timing chain slack in degrees?
Ignition timing?
Vacuum advance setting (number of turns out)?
OEM air filter?


Also, how do you drive:
RPM shift points?
Tire pressure?
Cargo load or empty?
Mostly short trips or long highway trips?
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Unread 07-31-2013, 08:55 PM   #6
jred
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If I'm even moderately heavy on the gas pedal, my MPG drops from 17-18 down to 14. That's with the hard top on, and the 4.0L.
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Unread 07-31-2013, 09:00 PM   #7
Rproject
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You're a little low. A stock '87 with the 258 should have 3:07 gears in it. With a properly tuned carb, good plugs/wires/cap/rotor, a fresh oil change and clean air filter, you should be able eek out 16-17 mpg. Get a little heavy on the foot and that'll drop to 14 in a heartbeat.
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Unread 08-01-2013, 07:15 AM   #8
superj
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i get 8-12 depending on how i drive. stock tires and suspension
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Unread 08-01-2013, 07:49 AM   #9
vcallen7
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Max tire pressure, clean air filter, high grade gas, general tune up, those are the easy things. You could also rebuild the carb
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Unread 08-01-2013, 08:48 AM   #10
zeus87gn
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Quote:
Originally Posted by richtfan View Post
tires are 30-950r15
These are killing your fuel economy on the stock gears
You need 3.55's

Or you can remove your top, doors, back seat and spare tire to get a few more light poles down the road
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Unread 08-01-2013, 10:28 AM   #11
fourbtgait
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83 cj, 4.2, t5 tranny, bbd, no smog, 3.54 axles, 31x10.50 all terrain.
No top, 60mph on freeway and running around I get 14 mpg.
Best I've gotten is 16 mpg with full top, driving slower.

As others say, go thru your engine, tire size/gear ratio, drive slower.
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