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  #16  
Old September 16th, 2020, 09:54
Black1990jeep Black1990jeep is offline
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Re: Poor gas mileage help

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Originally Posted by Evan03 View Post
Mines a renix I only see 1 on sensor on it

Im off 5-7 with 33s and 3.55 gears.

With 307 im off 12-15 speedo reads slow.

I also use GPS to kow actual speed.
On my pickup I calibrate computer for tire size tht would be cool option on old jeeps im sure the new ones can.

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do not depend on an accurate speedo to assure the odo is correct. to measure mpg you need an accurate odometer, not an accurate speedometer. the speedometer and odometer share the input cable, but the odo is direct gear driven, the speedo is not, thus the speedo reading may be wrong, and the odo still correct.

for mpg measurements you need a good odometer, the speedometer is not needed, and checking and confirming the speedo for accuracy does NOT mean the odo is accurate.

You need to check to odo for accuracy, drive a known length to check or drive with GPS for distance to check. speed be darned, you are concerned with distance, not speed for mpg measure.
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  #17  
Old September 16th, 2020, 16:11
RCP Phx RCP Phx is offline
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Re: Poor gas mileage help

One thing that's simple/easy to check is the TV cable adjustment. That can definitely effect the trans hook-up.
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  #18  
Old September 17th, 2020, 19:42
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techno1154 techno1154 is offline
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Re: Poor gas mileage help

The 1996 and up do not have a a cable driven speedo but rather a digital sensor/sender i.e. two wires from the TC case to the dash gage.

In the absence of a GPS, the mile markers along the highway provides an excellent to measure distance traveled and the difference between the dash speedo and the actual distance traveled.

Here is the method I use,...

At a mile marker post I press the little button in the gage cluster that reset the trip meter to '0' .

I continue driving at my preferred speed.

As I pull alongside the other mile marker posts I check the trip meter to see how many miles or 10th's of a mile off the gage is.

At least 10 miles is required to establish some accuracy. More miles are even better. 100 miles will be an easy number to work with.

Again,, a GPS is not needed and speed is un important since all that is needed is distance travelled.

It have been years since I looked at mine but I seem to remember somewhere in the neighborhood of about 7 indicated miles, my XJ is about 3/10 of a mile further down the road.
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1996 XJ; 4.0L; AW4; NP231; SYE; D30 and D44; ECTED; 4.10 gears; 30X9.5 -15 BFG/AT/KO; 3" lift; Rusty's LCA; JKS ADJ UCA; Kevins ADJ Track bar; Drawtite Front Receiver; Dual Electric Fans; Dual Battaries.
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  #19  
Old September 19th, 2020, 07:32
Grey Crawler Grey Crawler is offline
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Re: Poor gas mileage help

Ok, getting back on track. Let's just say that the speedo and odometer are both reading accurately. They were checked with my gps. What other issues might cause poor mileage? Specifically, a 35% drop.
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  #20  
Old September 19th, 2020, 07:42
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Tim_MN Tim_MN is offline
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Re: Poor gas mileage help

Expect lower mpg's because 3.55 axle gear ratio is so far off for 32's.

The primary suspect for a 30%-40% drop in documented normal mpg's is O2 sensor issues: Bosch or parts store brand sensors sensors instead of the NTK, worn or damaged O2's, defective O2 wire plugs or wiring harnesses, blown O2 fuses.

Install a cat converter.
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Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.

Last edited by Tim_MN; September 20th, 2020 at 05:40.
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  #21  
Old September 19th, 2020, 08:07
Grey Crawler Grey Crawler is offline
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Re: Poor gas mileage help

I agree, but 3.07 gears with 29s is equally bad. Why Bosch instead of NTK?
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  #22  
Old September 19th, 2020, 08:09
RCP Phx RCP Phx is offline
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Re: Poor gas mileage help

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Originally Posted by Grey Crawler View Post
Ok, getting back on track. Let's just say that the speedo and odometer are both reading accurately. They were checked with my gps. What other issues might cause poor mileage? Specifically, a 35% drop.
Gear ratio would effect the PCM / TCU inputs so the correct speedo gear
Over-all trans health (trans cooler, shift kit, correct ATF, etc)
Properly adjusted TV cable to insure good pressures
Good tires with correctly inflated air pressures
A cat or O2 sensors going bad
Any of the engine sensors failing, I don't see where you did any scanner testing

I'm at 5.5" on 32's with a 325+ HP stroker engine and get 18mpg on the highway!
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  #23  
Old September 19th, 2020, 08:10
Grey Crawler Grey Crawler is offline
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Re: Poor gas mileage help

Sorry, I think I read that part wrong about the Bosch and NTK.
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  #24  
Old September 19th, 2020, 08:13
Grey Crawler Grey Crawler is offline
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Re: Poor gas mileage help

Yes, I have a scanner. No codes
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  #25  
Old September 19th, 2020, 08:50
RCP Phx RCP Phx is offline
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Re: Poor gas mileage help

I wasn't referring to codes I was talking about "live data".
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  #26  
Old September 19th, 2020, 11:19
RCP Phx RCP Phx is offline
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Re: Poor gas mileage help

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Originally Posted by Grey Crawler View Post
I have changed o2 sensors, map sensor and switched to 4 hole injectors with no difference. I also have the cat delete. Any advice?
I would also question all of this plus you make no mention of your ignition system?
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  #27  
Old September 20th, 2020, 05:44
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Tim_MN Tim_MN is offline
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Re: Poor gas mileage help

The testing and repairs have been recommended, the questions have been answered, asking them again won't change anything.



Any relation to bimmerjeeper ?
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Quote:
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Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
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