Fuel gauge stopped working

[n33k0]

Greetings

The fuel gauge in my truck has stopped working. Luckily I noticed before I ran the tank dry. It is stuck between the 1/4 and 1/2 marks. This past weekend (and for the next few days) it has been raining constantly, and my truck is not very water-proof. Water leaks in to the cab, behind the dash... could the leaks have done something to kill the gauge? If so, where would I start looking for problems?

It had been working for the past year, although it was not working perfectly. The tank looks to be a blazer tank, located under the bed. I would fill the tank until the pump shut off automatically, and the gauge would only read 3/4 full. I'd drive until the gauge reached the short line between empty and 1/4 (which would mean 1/8 fuel left), and refill the tank, but it would only take 11-12 gallons (aren't blazer tanks 20gal?). I've never gotten brave enough to drive it till it ran out of gas to determine if the gauge needle was off or if there was an actual problem with my sender.

[kehstr]

Could you post a picture of the tank, i could tell you right off if it's a blazer tank or not.

[n33k0]

Here is the tank.



The filler neck and cap is offset to the left of the bed

[kehstr]

unless it was cut and edited, that is not an original blazer tank. A factory blazer tank filler neck comes out the drive side, about where the rear side marker light is. I don't think the water getting in the dash really would be a problem, the fuel level sender is probably just stuck in the tank. Or the needle on the gauge could just be stuck, does the needle go down when you turn the key off?

[tdangle]

The way to determine if it is the sending unit or the gauge itself is as follows:

1. disconnect the wire from the sending unit (typically a brown wire) it should read empty
2. ground the wire from the sending unit, the gauge should read full.

If this works, then it is the sending unit. If not then the gauge may have a problem.

Good Luck

[907debow1234]

Also having this problem..love to hear how ya solve this...

[n33k0]

Originally Posted by kehstr

unless it was cut and edited, that is not an original blazer tank. A factory blazer tank filler neck comes out the drive side, about where the rear side marker light is. I don't think the water getting in the dash really would be a problem, the fuel level sender is probably just stuck in the tank. Or the needle on the gauge could just be stuck, does the needle go down when you turn the key off?

No, the needle is stuck in place.

The previous owner didn't specify what tank it was but from the pictures I've seen it looks a lot like a blazer tank. Would it be unrealistic to assume the filler was modified to sit in the bed rather than the usual side filler (considering it's a stepside)? I've done some light research over the past year trying to determine what tank I have but I can't find any instances where someone has less than 19-20 gallon tanks (aside from custom made fuel cells). I don't know enough about these trucks to completely rule out a 12± gallon tank, but like I said before, I've never been brave enough to run it dry and see how much it takes to refill.

[n33k0]

Originally Posted by tdangle

The way to determine if it is the sending unit or the gauge itself is as follows:

1. disconnect the wire from the sending unit (typically a brown wire) it should read empty
2. ground the wire from the sending unit, the gauge should read full.

If this works, then it is the sending unit. If not then the gauge may have a problem.

Good Luck

Thanks for the tip, Terry. Reaching the sender will require dropping the tank; maybe I can take this opportunity to re-finish the bed wood and double check all the bed bolts. The tank does a great job making the farthest bed bolts impossible to reach.

[n33k0]

I unplugged the tan/brown wire going to the fuse box marked "FUEL GAUGE" and the gauge slowly moved past the FULL mark



Then I plugged the tan/brown wire back in and the gauge reset to the "full" tank spot like it has since I bought the truck.



The tank is full, I filled it up as much as it would take last night. I drove a few miles today and the gauge didn't move much, so I'm not sure if it is working as it used to or if it is now stuck at that new position.

[XwalkerX]

did you ever figure this out?

[snipescastle2]

That tank looks like the "LMC" tank I bought, I'd say either the sender has gone bad, or the wire from the sender to the gauge has a short/break.
Ben

[tdangle]

Yep, to me it looks like a bad sending unit. If the wire is open, then the gauge will read full + if the wire is shorted it should read empty. Looks like you need to pull the tank or somehow get access to the sending unit.

[davepl]

Incorrect, bad, or malfunctioning sending unit with too high of resistance. If you KNOW the float is sunk and its not reading empty, it's hooped.

Basically you can think of the gas gauge as a measure of "how much flow" or "how little resistance", and the higher the tank, the more resistance.

Full tank is high resistance, so Full reading. Disconnect the wire is infinite, so higher than full. Shorted wire would be no resistance, or empty.

You have, in all conditions, too much resistance. Could be as simple as resistance in the ground path too. But you need to find out where the extra resistance is coming from.

Right at the sender, from memory, it should go from 0 to 90 ohms (empty to full).

[n33k0]

Thanks for the info, guys. After a few days of driving the truck the gauge started moving again. I kept an eye on it over the weekend and it seems to be back to "normal". It still displays the incorrect amount of fuel but at least I can see when it is near E and I know I should fill up or tempt fate (Even though I don't trust the gauge too much anymore, I just use my odometer to guess how much fuel I have left). I haven't had the time to go through the mess of wiring on the truck or drop the tank and check out the sender, that is next on my to-do list.