JK computer sucks - JeepForum.com

 
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post #1 of 15 Old 02-23-2007, 06:55 AM Thread Starter
strykermp5
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JK computer sucks

so... i am almost on the red line on the gas gauge... and apparently, i have 45 miles left in the tank... LOL

working for an attorney... i should run out of gas, take a video of the downed vehicle and the computer. Then sue them for misrepresentation of a vehicle... haha


all joking aside, has anyone else noticed this??


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post #2 of 15 Old 02-23-2007, 08:35 AM
boidy7
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yeah once i hit a quarter of a tank i gotta find gas QUICK!
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post #3 of 15 Old 02-23-2007, 09:04 AM
PJRedd
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From the owners manual:

1. Fuel Gauge
The pointer shows the level of fuel in the fuel tank. When
the fuel gauge pointer initially moves to E, for your
safety, approximately 2 U.S. Gallons (7.6L) of fuel remain.

Because it woultn't be safe if E actually meant empty?
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post #4 of 15 Old 02-23-2007, 10:45 AM
redrom01
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Dont forget that the owners manual tells you how big the fuel tank is. So when I get down to E and only fill up 16 or 17 gallons I know that I'm not actually close to E.

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post #5 of 15 Old 02-23-2007, 11:03 AM
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I got lost using the built in compass on my JK, I had my ham radio on the top of the dash above the stereo and the magnet from the speaker of the ham radio messed up the compass and no matter what direction I was facing it always showed SE.

I was driving in cirlces at the mall parking lot for 5 hours before I figured out I wasnt going anywhere

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Thanks, if it is that good than I'm sure that they can't sell it in California. Everything else is illegal in this state except the illegalsl
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post #6 of 15 Old 02-23-2007, 07:57 PM
XJ2Timer
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Quote:
Originally Posted by redrom01
Dont forget that the owners manual tells you how big the fuel tank is. So when I get down to E and only fill up 16 or 17 gallons I know that I'm not actually close to E.
You are closer than you think. Any crud in the tank settles to the bottom as well as any water that separates from the gas. To keep that stuff out of the fuel pump, injectors and engine the pick up tube does not go to the bottom of the tank.

My old '89 Cherokee the gauge was calibrated where when it hit empty I could drive another day around town and not run out of gas. On my '01 Cherokee when the low fuel light comes on I have maybe 5 miles before the gauge needle drops from a sixteenth of a tank to empty. When it hits empty I better be at a pump. I ran out of gas once soon after I bought it. When I filled it up I could only put 17.5 gallons into the 20 gallon tank.

Remember when the computer monitor makers were sued and then had to label the monitors with the actual viewing size of the screen? Wish the auto makers had to do the same. If they claim a 20 gallon tank on my Cherokee than that ought to be 20 usable gallons. Not 17.5. At 20 mpg on the highway I ought to be able to drive 400 miles then run out of gas not 350.

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post #7 of 15 Old 02-23-2007, 08:00 PM
igofshn
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Quote:
Originally Posted by XJ2Timer
You are closer than you think. Any crud in the tank settles to the bottom as well as any water that separates from the gas. To keep that stuff out of the fuel pump, injectors and engine the pick up tube does not go to the bottom of the tank.

My old '89 Cherokee the gauge was calibrated where when it hit empty I could drive another day around town and not run out of gas. On my '01 Cherokee when the low fuel light comes on I have maybe 5 miles before the gauge needle drops from a sixteenth of a tank to empty. When it hits empty I better be at a pump. I ran out of gas once soon after I bought it. When I filled it up I could only put 17.5 gallons into the 20 gallon tank.

Remember when the computer monitor makers were sued and then had to label the monitors with the actual viewing size of the screen? Wish the auto makers had to do the same. If they claim a 20 gallon tank on my Cherokee than that ought to be 20 usable gallons. Not 17.5. At 20 mpg on the highway I ought to be able to drive 400 miles then run out of gas not 350.
I have not looked at this fuel pump but on a tj the pick up is at the bottom of the tank. I'm sure this is also.

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post #8 of 15 Old 02-23-2007, 09:50 PM
2k2wranglerx
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i've put over 20 gallons in my tank before.

93 yj. 355 chevy, heads, cam, intake, etc. 35's, bumpers, winch, lights, and a killer stereo.
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post #9 of 15 Old 02-23-2007, 10:36 PM
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Average fuel useage on the computor read 19.2 miles per gallon, but when I do the calculations I get 17.2. anyone else see this problem.
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post #10 of 15 Old 02-23-2007, 11:28 PM
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I think the fuel sensor used in automobiles was designed by the same guy at about the same time as he designed the water float valve used in toilet tanks. Seriously, it's just a float on the end of an arm that moves across a wire wound resistor. It is barely one step above a hole in the top of the tank that you put a stick into.
I had a 78 CJ that was always at a half tank; didn't matter how much actual fuel was in the tank, it always read half full (or empty for some of you).
So now, I go by the mileage. I average so many miles per tank, and when I get to that number I fill up.
In my new Jeep when the light comes on I have put in anwhere from 13 to 17 gallons.

Steve

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post #11 of 15 Old 02-26-2007, 07:28 PM Thread Starter
strykermp5
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screw it... i put a piece of black electrical tape over...

computer?? what computer?? mine musta not come with one.

oh well!

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post #12 of 15 Old 02-26-2007, 08:35 PM
MichaelW
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Well being from Nevada where there are places with 300 miles between stations. I always carry a full gas can when not in town. I don't use the gage but my odometer as a general rule and never go more than 300 miles between fill ups. Regardless of what the gage may say.

I will be one of the first in line to buy a second tank and transfer system if one comes out for the JK.
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post #13 of 15 Old 02-28-2007, 08:17 AM
JeF4y
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Quote:
Originally Posted by chevyjeep
Average fuel useage on the computor read 19.2 miles per gallon, but when I do the calculations I get 17.2. anyone else see this problem.
Yep... my computer calcuation must have been designed by someone in marketing. It's off by as little as 2 and as much as 5mpg... most of the time it's 3.5 mpg off... Off to the point that it's totally unreliable from a user perspective.

Great feature

But it should come in handy when people start selling these things used!

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post #14 of 15 Old 02-28-2007, 10:11 AM
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From what I've observed personally and read from other posters on a certain JK-specific forum, it seems like the mileage computer takes multiple point-in-time samples of fuel consumption and averages them out --- The problem lies in the sampling timing and limitations; the computer captures only so many inputs (let's say 10, for argument's sake), and overwrites older readings with those new inputs... so in essence, you end up with a "rolling average" of the last 10 (or however many) inputs the CPU recorded...

I've read from some posters (who have let their JKs warm-up in the morning for extended lengths of time) that their mileage reading from the CPU is DRASTICALLY reduced from warm-ups... as for me, if I warm up my JK for 5 or 10 minutes in the morning, I'll see at least a 0.5 mpg drop in the reading the CPU displays.

Oh yeah - one other thing: Most people have observed that the mileage computer gets more accurate when two things happen:
1) the CPU "learns your driving style" and adjusts the shift points to match, AND
2) the engine is fully "seasoned" by 3,000 or more miles of use.

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post #15 of 15 Old 02-28-2007, 11:31 AM
Jeeples
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Quote:
Originally Posted by PJRedd
From the owners manual:

1. Fuel Gauge
The pointer shows the level of fuel in the fuel tank. When
the fuel gauge pointer initially moves to E, for your
safety, approximately 2 U.S. Gallons (7.6L) of fuel remain.

Because it woultn't be safe if E actually meant empty?

You're kind of correct there.

Modern in tank electrical fuel pumps are made so that the gasoline in the tank provides provides lubricity and a cooling for the fuel pump. Running your system entirely out of gas or even down to the last gallon can cause damage to the pump as the moving parts are not being lubricated properly (just like an engine).

I am going to assume the 2 gallon mark is where the fuel pump is still fully submerged in the tank, thus providing a small safety net for the full pump. Because of this, DCX calibrated the fuel gauge to read empty so that people aren't burning up their fuel pumps within a year of purchase.

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It is what Jeeples has *PARTIALLY* stated.
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