Gas Gauge not working properly
 

I recently had the single gas tank replaced on my 1996 F150 XLT (302, M50D Std Cab, Short Bed) with a Spectra Tank Assembly. It came with a fuel pump and sending unit already installed. It works great, the truck even runs smoother and seems to have better acceleration and I my gas gauge has functionality again. Problem is, it doesn't go all the way to full when I fill the tank. It will usually sit at 3/4, and when the truck sits for a while, it will sit even lower. Now I know these things are gas hogs, but one day I went to start my truck and my gauge read 1/4 full with 50 miles on the trip! So either I'm getting 3 mpg on the highway, or my gauge isn't working properly. Is there any fix for this? Now I know the sending unit is usually the culprit for these kind of issues but it's a brand new unit, as well as a brand new pump and tank. I've heard it may be something to do with a voltage regulator but I'm not entirely sure. I just want this thing to work properly so I know how much fuel I have! Any help would be greatly appreciated.

You do not have the voltage regulator in your cluster for the gauges like some older trucks in the 80's had.

If the gauge worked OK before replacing the tank I would say a bad sender in the tank. If it worked OK before and you still have your old sender plug it in and see what the gauge does as you operate the float up and down. The plug is on the drivers side frame rail.

That's just it; my gauge didn't work with the original tank, sender, etc. When I would start it the needle would jump to a random spot and stay there. I have a hard time believing that the sending unit is already bad, it has about 80 miles on it, as with the tank and pump.

I would just swap in another gauge. Just get one out of a cluster at a salvage yard cluster and pop it in.

I mean I don't think it's the gauge. When I got the truck back from the shop and filled it up, the needle went to just above 3/4 of a tank. Recently, I filled up my truck (19 gallons), and have driven about 80 miles on that tank. The gauge is reading just above empty now, which would mean I'm getting 4 mpg on the highway if the gauge is accurate. I've heard that you can test the gauge by moving the float up and having someone watch the gauge and see if it moves properly. Could it be a wiring issue? This is the tank I got for the truck ( ). It fits the F150 even though it says Chevy, I just bought it on Amazon because free 2 day shipping haha. I mean, I have a hard time believing that the sending unit is already bad or it's not calibrated right. It's brand new! It's just a frustrating problem that I thought would be resolved with the new tank and stuff and I just want it to work properly.

I have no idea how a GM gauge sender works as I do not work on GM trucks.
Sorry I can not help you with GM parts on a Ford truck.

I would say you need to buy a Ford fuel tank, an a Ford fuel sender & pump.

Fuel system senders and gauges, in general:

GM
Little resistance, empty. Much resistance, full. (0-90ohms)

Ford and Chrysler
Much resistance, empty. Little resistance, full. (73-10 ohms)

Your gauge is a Ford and your sender is a GM? If that is the case, the system will never read properly. Down is up and up is down, and the values don't match.

If your sender is a Ford mounted in a GM location, the geometry of the sending arm won't match the profile designed by Ford. The sender does not "know" the empty and full points, like a pitcher who can throw 60'6" and does not "know" where the mound is. He might have a great fastball, but it does no good when he is standing in left field.

I hope this helps.

Ok well it's not a GM assembly. Idk why Amazon says it is, but every other parts website says that the Spectra Part # F1G1FA (my assembly) is for Ford Trucks from 1990-1997. O'Reilly says it, Rock Auto says it, etc. I only bought it from Amazon b/c of the price. I did my research, it's a Ford spec product.

Then I would do what I said in post #4 above and see what happens.