My 99 XJ is getting terrible gas mileage - Page 2 - JeepForum.com

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post #16 of 22 Old 06-30-2013, 04:50 PM Thread Starter
Charley3
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1999 XJ Cherokee 
 
Join Date: Mar 2013
Posts: 5,538
How about a Hesco 62mm TB with Hesco 62mm spacer?


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post #17 of 22 Old 07-01-2013, 08:30 AM
Evildriver-3
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1995 ZJ 
 
Join Date: Mar 2005
Posts: 957
Im a F&B user when it comes to TB's, but the hesco tb would help, not sure how the spacer would really effect anything in f.i. i never seen a diff on my jeep when adding plates for other issues beneath my f&b

1995 Jeep gc ltd, 2005 Jeep gc ltd , 71 Dart, 73 RR 440-6pk, 78 Mag GT, 85 Power Ram W-350, 92 Daytona, 99 Dakota, 08 Ram 2500

Less than 8 is like playing with half a deck
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post #18 of 22 Old 07-19-2013, 11:40 PM Thread Starter
Charley3
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1999 XJ Cherokee 
 
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My gas mileage at 60 mph has improved from 16 mpg to 21 mpg. I think that's good for 30 x 9.5 R15 tires that are on the low end of acceptable street pressure.

New plugs, wires, cap and rotor didn't make much difference.

My latest tweaks were motorvac (similar idea as Seafoam), a new oxygen sensor, and a 205F thermostat. Since all 3 of those things were done at same time, I don't know how much gas mileage increase came from each mod.

I do know that on an LJ in the past I had a 205F stat put in and gained approx 2.5 mpg. So I assume that my XJ gained around 2.5 mpg from the 205F stat.

I think the other 2.5 mpg improvement is from the motorvac, the oxygen sensor, or both. Not sure.

Prior to replacing the oxygen sensor, it was tested by a Napa car care center. They told me the oxygen sensor was fine, but I insisted they replace it

Power at mid rpm has improved some too.

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post #19 of 22 Old 07-19-2013, 11:55 PM Thread Starter
Charley3
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1999 XJ Cherokee 
 
Join Date: Mar 2013
Posts: 5,538
Tomorrow my cousin and I will be installing a high flow cold air intake.

I hope to gain another 2 mpg from that.

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post #20 of 22 Old 07-21-2013, 02:16 AM Thread Starter
Charley3
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1999 XJ Cherokee 
 
Join Date: Mar 2013
Posts: 5,538
My cousin installed an AFE "Cold" (cooler) Air Intake with dry filter in my XJ today.

I immediately noticed it idles a little faster and smoother. Is slightly faster idle normal with a high flow air intake?

I noticed better torque at low rpm, and better torque and power at mid rpm. I didn't test high rpm.

I have not retested gas mileage yet, but I expect some improvement.

Very happy with AFE "Cold Air Intake. I'm glade I chose their dry filter intead of their oiled filter.

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post #21 of 22 Old 07-23-2013, 10:02 AM
Evildriver-3
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1995 ZJ 
 
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The stat and o2 definitely helped, the afe is good for cooler air, not sure you'll see 2mpg from that, maybe some percentage of but i have never seen huge improvements there

1995 Jeep gc ltd, 2005 Jeep gc ltd , 71 Dart, 73 RR 440-6pk, 78 Mag GT, 85 Power Ram W-350, 92 Daytona, 99 Dakota, 08 Ram 2500

Less than 8 is like playing with half a deck
]=Supershafts=[
Long Island Motorsports Association
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post #22 of 22 Old 07-23-2013, 02:02 PM Thread Starter
Charley3
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1999 XJ Cherokee 
 
Join Date: Mar 2013
Posts: 5,538
Quote:
Originally Posted by Evildriver-3 View Post
The stat and o2 definitely helped, the afe is good for cooler air, not sure you'll see 2mpg from that, maybe some percentage of but i have never seen huge improvements there
I got 1 more mpg from the AFE, and I also got better power for hills. So it's good.

The AFE flows really free. It even starts easier and idles smoother! Noticeably more mid rpm power on hills. Haven't tried high rpm.

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