Ever since I finished my harpoon mod, my fuel guage has been incredibly off. It will stay slap full for approximately 250-300 miles (yes i realize since the capacity is greater it will stay longer, but damn, 300 miles?). It took me three attempts to finish the mod though. My first try I was pressed for time and I had to wrap it up about the time I got the fuel tank down. The second time, I got the tank down a lot faster, but I could not figure out how to get the fuel lines off of the sending unit cap, so I was going to try and just slide the tank out of under the truck and leave the sending unit hanging. As I was sliding it out (i thought the whole sending unit was out) I saw that there was a wire still down in the tank, so I looked to see what it was and it was the guage float being pulled on. The third time I tried it I figured out how to get the fuel lines off so I finally got the tank out and the sending unit out and the guage float wire didn't look like it had any un-natural bends in it, just the normal (approximately 100-120 degree) bend that's already there. So does anyone know what I could have done to make it not work right? I made sure when I put the sending unit back on that I lined up the tabs with their slots and the float was pointing towards the back of the tank. Also, since I have done it, my water in fuel light has been coming on a lot, and I have drained it 3 times in a matter of a month and a half, and on the third time I changed the filters and it still comes on. Could this be a result of the harpoon for some reason? Let me know what information you got. Thanks in advance.

 

Most car/truck gages are not linear. Assume you had a 40 gal tank. You would expect a 1/4 tank movement and the same mileage for every 10 gallons if the gage read linear. You made this problem worst by adding extra capacity on top of the already optimistic first 1/4 tank. You can bend the float arm upward to make it move off the top faster but it may show empty when you have plenty left. It’s all about the angle of the arm in relation to the top of the pump assembly. It's just a guide to how much fuel you have. Like I said if it bothers you put an upward bend in the arm, not too much you don't want your truck to say empty with 1/4 tank left.
Remember the old toilets tanks with the arm and a big float on the end? Same thing!

I Laugh when I hear people say I get better mile when I have a full tank.
Hand check you mpg at 3/4 and 1/4 you will see very little difference even when you get 300 miles out the first 1/4 tank.

 

its possible you bent the arm and didn't realize it. ie changed the angle of a factory bend. the water in fuel sensor was an issue on the 03 in particular many were changed under warranty because they corroded and indicated water all the time. it may be possible to dismantle the hfcm and clean the corrosion and get it working. the other possibility is that you're getting crappy fuel. try to catch the fuel you drain in a clean clear container and examine it to see if you really have water in the system. good luck

 

That still doesn't make any sense as to why my fuel guage isn't working properly. Like I said, I understand that I increased the tanks capacity, therefore increasing the amount of miles that it will stay on fuel, but once the fuel got down to the float's "high-water mark", the guage should function as it normally would. I couldn't care less how long it stays on full, I just want it to go down at whatever rate it should once the level comes off of full.

And for anyone else who reads and may have misunderstood me, my question was not why it is staying on full longer, but my question was "What could I have done to make it think I still have a little over half of a tank when I am actually out of fuel?" But I think Nitrogen answered that question, although when I inspected the rod it did not look like it had any abnormal bends in it. Usually if the rod was made that way, and you try and bend it back out, it's nearly impossible to bend it out and make it look natural. But anyways, now the question is how to get it "straightened out" CORRECTLY, EASILY, and CHEAPLY.

This, however, makes sense. If I were to have over-extended it, that would mean that once the float gets to the bottom of the tank, it would still be reading higher up at it's pivot point. The only problem with me getting up in there again and trying to fix it (other than the fact that I swore once I got done with the harpoon I would never touch the fuel tank again) is that I have no idea what the standard angle looks like, therefore I would have no idea where to bend it back to. You think a shop or, god forbid the stealership, could straighten it out for me without bull-****tin me and telling me I need a new fuel pump/sending unit?

Oh and btw, thanks for your info on the HFCM. I'll have to get up in there and check it out one day when I have some time.

 

well it sucks to have to drop it again. but if you had it emptied, dropped it down then put in a specific volume back in say 1/4 tank then install the gauge with the tank on the ground you could bend it a little at a time until it showed the right reading at the gauge. i don't know if the wiring harness would have enough slack or if you would have to fab up an extension cord to reach with the tank down, but it might be worth a shot

 

Definately some creative thinking! It would definately have to be a day when I had nothing to do, because it probably takes the sending unit a little while to register with the guage, otherwise your guage would constantly be moving depending on how steep of a grade you were on (which a friend of mine's 94 350 does).

 

yup takes a couple minutes to register a change. could result in many cold beverages being consumed while waiting. hic hic hiccup

 

Shoot, in this weather? More like a lot of coffee or hot chocolate!

 

I wondered what happened to the Harpoon King. With a volt/ohm meter check the float - unplug the gauge wires- at the bottom of the tank it should read about 15 ohms, when raised to the top-full tank-it should read about 160 ohms. Being that the float is on that Z bent spring wire make any adj bends with pliers for a crisp bend. At least you will know if the float / sender is correct and functioning. Good Luck