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post #1 of (permalink) Old 04-11-2003, 08:23 AM Thread Starter
 
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TJ fuel ecomony

My 4.0 auto is averaging 200-210 miles per tank, 30" stock tires. My best was 240 per tank, with a 220 average. It seems to have gotten very bad very quickly, which is making me think the computer is getting a wrong reading. The motor has 59K on it, fully tuned, new air filter, and Mobil 1 only. It also flew through NY State inspection in January. Is 12 miles per gallon average for anyone else, and is there a self diagnosis test I can do to check the sensors? I used to be able to do the self test on my '94 (the key on key off 3 times I believe), is it the same for TJ's? Also, does anyone have the code listings?
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post #2 of (permalink) Old 04-11-2003, 09:45 AM
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Re: TJ fuel ecomony

1991-1997 the Powertrain Control Module (PCM) can be put into a diag. 1998-present a service department is needed. If there isn't the proper scan tool avaible *


*I looked it up in a...Jeep repair manual.*


post #3 of (permalink) Old 04-11-2003, 11:50 AM
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Re: TJ fuel ecomony

My 2001 4.0L Automatic Wrangler gets about 200 miles before the little gas warning light turns on. That is mostly city driving with 3.73 gears and 225/75 15 tires. My TJ does have a diagnostics test built into the digital odometer. You turn the key on and off 3 times (check this to be sure) and it shows a code number on the odometer for a few seconds. You look up the code in the service manual and it tells you what the problem is. My check engine light came on and I performed this test. It showed I had a mild vacuum leak in the gas tank vapor return system. Easy to fix once my jeep told me what the problem was!
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post #4 of (permalink) Old 04-11-2003, 12:11 PM
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Re: TJ fuel ecomony

How do you clear the memory after repair without a scan tool? Disconnect the battery?
post #5 of (permalink) Old 04-11-2003, 12:12 PM Thread Starter
 
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Re: TJ fuel ecomony

Thanks, I check the codes tonight. Anyone have a copy of the codes?
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post #6 of (permalink) Old 04-11-2003, 02:03 PM
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Re: TJ fuel ecomony

When I had my YJ with the 258, I was getting around 18 with mostly highway driving. Now that I have a TJ, I was getting 18 in Colorado but now I live in Washingtom and don't drive the highway as often. I think my mileage is in the 14 - 16 range but I tend to follow the little shift light and not hot rod her around. Might check the pressure in the tires. I tend to run mine more than others so that I can get some mileage out of every gallon. I run around 30 psi and it isn't to rough a ride.

HTH,

Daren

98 TJ 4" lift
32 11.5 15
Stock gearing
post #7 of (permalink) Old 04-11-2003, 04:37 PM
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Re: TJ fuel ecomony

From what I gathered from the DC Service Manual, the codes reset themselves. The vehicle has to operate for a given period of time without detecting the error, and then it resets. I drove my Jeep for about 2 days before the check engine light went off. The odometer has a code (I do not remember what it is) if there is no error in its memory.
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post #8 of (permalink) Old 04-11-2003, 07:15 PM
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Re: TJ fuel ecomony

I was reading frome the Haynes manual. There is a code list in there. The note before the self diag suggests that a scan tool is necessary.?.?

I going to go play with it this weekend.

Heck if it could be done without a tool . Why buy something.
post #9 of (permalink) Old 04-11-2003, 07:50 PM
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Re: TJ fuel ecomony

1. This should help... [img]images/graemlins/grin.gif[/img]
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