Early low fuel warning light (comes on around 5/8 full tank)

Catmonkey

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The sending unit in the tank might either be defective or something is restricting the float from going all the way down. I have no idea how the trip computer calculates MPG. I have run larger injectors in a couple of different Ford applications with the trip odometer, so I don't believe that is an issue in the calculation. I have an app that I use to keep track of actual fuel consumption in all my vehicles. The trip computer isn't all that accurate with a bias to make you think your mileage is better than it is. At least that's been my experience with 4 different Ford vehicles.
 

JB_2010GT500

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This happened after Pro Edge Tuning did a tune, pulley swap on my 2.8, installed ID1000s, TR7IX, Dynatech headers, and a MBRP exhaust back in the summer of 2015. I have dealt with it ever since. Bill Miller wasn't sure what was causing it. I also have a Lund tune and the gas mileage issue remains. Lund Sr doesn't think it's tune-related. I had my mechanic reprogram the instrument cluster just now and that hasn't fixed it either.

It is very frustrating to have a low fuel light that comes on after driving 40-50 miles.


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JB_2010GT500

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Imak--I didn't do the diff swap until spring of last year... this issue started before then.


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Catmonkey

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This happened after Pro Edge Tuning did a tune, pulley swap on my 2.8, installed ID1000s, TR7IX, Dynatech headers, and a MBRP exhaust back in the summer of 2015.
May just be coincidental. I use PRP to tune my car and there are no parameters dealing with gas gauges or anything related to it, so I honestly don't think you can cause this issue with a tune, much less changing out the parts that were upgraded. Can't hurt to have someone pull the pump and operate the float manually to see if changes the reading on the gauge. If it does, you need to figure out what's binding the float's movement in the tank. If it still hangs up at 3/4 tank with the low fuel light, you just need to rule out if it's the sending unit on the pump or the fuel gauge.
 

JB_2010GT500

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Thanks Catmonkey. So it's not possible that ID1000 injectors can throw off the trip computer's calculation of how much gas is being used?


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Catmonkey

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I'm not seeing it. I ran both ID750 and running the ID1000s now. I think you're going to get worse mileage because of the larger injectors and supporting mods, if you tap that power, but that's just part of the game. My old F-150 had 39 pph Cobra injectors in place of the 19 pph stockers, when I supercharged it, and I never noticed any difference in the mileage display. I drove it for six years with quite a bit of mileage. I usually took it on trips, so it saw a lot more highway miles than the Shelby.

A lot of my mileage is in town and I average 12.5 when it's all in-town. In-town for me is a lot of stop and go at long signals. When I do get it out on the highway, I get the advertised fuel economy. My old F-150 and my 2015 F-150 ecoboost see similar in-town mileage as the Shelby. Granted the ecoboost only has a tune at this point.
 

Ninjak

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When in the town the mileage for me is lower as well. I took my car to Orlando and the mileage was much different. In truth I could have made it to Orlando on one tank of gas. (Mia to Orlando=230 miles)

I have my car tune by Pro Edge, I never thought it had anything to do with the tune, I just thought the computer would go off after a while. If I reset my system its ok again for a bit, then it creeps back. In truth its always done it at a 1/4 tank, but never higher than that.
 

JB_2010GT500

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True. But if I reset my trip odometer when I fill up, drive 150 miles, then fill up again and put in 12 gallons, I calculate my actual gas mileage to have been 12.5 mpg on that tank of gas. But the trip computer always settles in the 6 mpg range and is therefore incorrect. Plus it is clearly using the 6 mpg number to estimate remaining miles to empty, hence the early low fuel warning.

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jazz

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It might be the level sender, mine sometimes stays at empty, i took it out and moved it up and down, started working now. Going to drive it around for bit to see if it will stay working. If not then might have to replace it
 

JB_2010GT500

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I wish I had an electrical diagram for the trip computer to see where it is getting its inputs for miles to empty and average mpg. Even though it's clearly off, the "mechanical" fuel gauge has always read the correct fuel level.


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ShelbyGT5HUN

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Just a thought, check your revs per mile setting via your hand-held. Maybe there is an incorrect value there (too high of a value). If the computer is computing miles per gallon, and your revs per mile is off, that could be the problem.
 

SCGallo2

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Did your new magnum XL transmission come with a OSS (Output Shaft Speed) sensor, or did you reuse the one off your T6060? I've dealt with this before with upgraded pumps, ID1000s, and my Lund tune, but once we corrected my rear gear ratio and tire revs per mile in the tune, I did a KAM reset and all was well. My JDM tune worked perfectly with stock pumps and ID1000s. Did you ever check your actual MPH with GPS while driving to see if your speedo is accurate? Sounds like your mechanical fuel level indication is working properly to me.
 

Catmonkey

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I'm under the impression your gas gauge stopped at 5/8. Now I'm not so sure that's the issue.
 

JB_2010GT500

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I haven't checked but it should be pretty close given my spreadsheet calculations which have rpm, gear ratio, and tire diameter. I'm not sure about the output shaft speed sensor. I will have that checked out. Yes, the mechanical gauge functions correctly at all fuel tank levels. My Lund tune is locked so I cannot change revs/mile.

As an update--I reset the mpg screen on my trip computer and have been babying the car (staying out of boost). The trip computer has settled around 13.5mpg (I actually calculated more like 18mpg based on my most recent fill-up) and, slowly, the miles-to-empty seems to be re-calibrating to a more realistic level. I'll keep everyone posted.


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bigphill911

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did you ever figure this out I am having the same thing happen. Definitely using all the fuel because I can drive on 0 miles to empty for a long time and the gauge is working properly just the low fuel light is tripping way early.
 

JB_2010GT500

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did you ever figure this out I am having the same thing happen. Definitely using all the fuel because I can drive on 0 miles to empty for a long time and the gauge is working properly just the low fuel light is tripping way early.

No. But I upgraded my injectors and fuel pumps and the problem resolved itself. The miles to empty calc works fine now. One of those freak things...

Although now I have a new problem where my fuel gauge hangs around 3/8 full... hear that’s common for the big triple pump systems.


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