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Old 05-17-2013, 02:06 PM   #1
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Only 14.3 miles per gallon on new 4.2 L engine.

I put a new 4.2 L engine In my 1988 Jeep Sahara. And I'm only getting 14.3 miles per gallon whether I drive at 80 miles an hour or 65 miles an hour.
My old engine was getting 17 – 18 miles to gallon But it was fixing to crater.
Is there some sort of a harmonizer that you can hook up to the engine to find out If the engine or the carburetor or something is running rich .
If so what is the name of the machine I need to hook it up to.
I'm located in San Antonio Texas. Does anybody know of any shops that would handle that.

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Old 05-17-2013, 06:24 PM   #2
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Did You use the same Carb.? adjust it with vacuum gauge and set the timing and wait for it to break in.

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Old 05-17-2013, 06:30 PM   #3
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How much fuel have you ran thru the new engine?
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Old 05-17-2013, 11:26 PM   #4
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Did You use the same Carb.? adjust it with vacuum gauge and set the timing and wait for it to break in.
No it's brand-new carburetor.
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Old 05-17-2013, 11:27 PM   #5
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How much fuel have you ran thru the new engine?
About 35 gallons
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Old 05-17-2013, 11:28 PM   #6
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Did You use the same Carb.? adjust it with vacuum gauge and set the timing and wait for it to break in.
Hey thanks for answering
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Old 05-17-2013, 11:30 PM   #7
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How much fuel have you ran thru the new engine?
Thanks for answering
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Old 05-18-2013, 07:59 PM   #8
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Where did you find your new engine? I've been looking but can only find a rebuilt from Automotix..
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Old 05-18-2013, 08:04 PM   #9
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I have a 84 cj7 with a 4.2l. Great motor but the carb. was junk from the factory. Switched to fuel injection. Problem solved.
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Old 05-18-2013, 08:10 PM   #10
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Hey!

That engine needs to be broken in!!!!....tolerances may still be a little tight.....run it on dyno oil for a while and you will see the MPG and power slightly climb....

Later!
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Old 05-20-2013, 10:52 AM   #11
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How much fuel have you ran thru the new engine?
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Originally Posted by drwhitefox View Post
About 35 gallons
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Hey!

That engine needs to be broken in!!!!....tolerances may still be a little tight.....run it on dyno oil for a while and you will see the MPG and power slightly climb....

Later!
I was thinking the same thing. It's not uncommon for the fuel effeciency of an engine to get slightly better, with each tankful of fuel. But since he's gone thru at about three tanks, I'm thinking it's not going to get much better due to tolerances being tight.
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Old 05-20-2013, 12:22 PM   #12
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Heck I think my 93 Wrangler is getting about 20-25 MPG and I'm only using 3/4 of the 20 gallon tank.
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Old 05-20-2013, 12:30 PM   #13
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Wow I'm only getting 18 miles per gallon on my 94 yj
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Old 05-20-2013, 12:48 PM   #14
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not engine related, but double check your tire pressure and also make sure none of the brakes are dragging. A low tire, or dragging brakes will totally kill your mpg. Even 5 pounds low can hit the mpg quite a lot.
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Old 05-20-2013, 12:53 PM   #15
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My tires are brand new from the early 2000's because when the state of Oregon stopped using steel studded tires and went to aluminum studs. So my set of Radial Wildcats are really nice thick walled tires and balanced. Good thing I kepted them all these years.
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Old 05-20-2013, 02:20 PM   #16
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You guys are all lucky I get about 10mpg on a good day

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