View Full Version : Fuel sending unit issue!!

12-06-2015, 10:11 PM

I'm Tom and have a 72 Demon 340. I'm new to this forum but really need some advice. It seems my fuel gauge is Way off, when it registers E on the gauge it only takes 7 or 8 gallons to fill it and it reads full and will take no more. I take it out for a cruse and it drops to E in about 70 miles with the same only taking 7 - 8 gallons to register Full again. I sent the gauge to Red line Gauge works to be rebuilt and calibrated, put it back in and no change. So next step I changed the sending unit with a brand new one, you guessed it no change. So 2 sending units and 2 different gauges and still no improvement. I have to be missing something, any Ideas??
Any help will be greatly appreciated!!

Is there somewhere I can send the sending unit to be checked and or calibrated?? Just grabbing at straws at this point.

68Charger 440HP
12-07-2015, 12:52 AM
Does your fuel gauge and new sending unit operate within the same ohm range? They must be matched up in order to work right. For example, Auto Meter fuel gauge 3315 needs a sending unit that operates within this range: 73 ohms empty, 10 ohms full. (most Mopars) Your new sending unit should have specified the ohm range but they can be tested with a volt/ohm meter. You gauge should also specify what ohm range you need for the sending unit.

I have a similar problem with my charger although I haven't set out to fix the problem yet. I want to replace my fuel gauge (that was installed by the previous owner) but in order to get the correct gauge, I need to drop the fuel tank and measure my sending unit. I have no idea if the previous owner replaced the sending unit or matched it up with the proper gauge. To me it sounds like we have the same problem. The fuel gauge is reading your fuel level but just not accurately because most likely the ohm ranges aren't matched up.

12-07-2015, 04:45 PM
68 Charger,

My gauge and sending unit are both @10 ohm full and @ 80 ohm empty. When I set them up on the bench the sender an gauge read pretty close, now I'm thinking it's the geometry of the float is off. I'm going to try to change the lenth of the float on my spare unit and see if it changes for the better. I'm thinking if I make it longer it should give me a longer and hopefully more accurate reading. I'll let you know how it works.

12-07-2015, 08:40 PM
Is the sending unit OEM or a knock-off?

12-08-2015, 08:38 PM
there are no new oem

John Kunkel
12-09-2015, 02:09 PM
Are you sure the sending unit is properly grounded? Is there a clip-on ground strap between the metal fuel line and the metal nipple on the sender?

12-10-2015, 12:48 AM
there are no new oem

True, they haven't been made for years but every now and then, some NOS pops up on ebay or swap meets.

12-10-2015, 10:17 PM
I'm with John on the ground. Sounds like a ground issue.

68Charger 440HP
12-19-2015, 06:06 PM
What was the verdict Mr.FT? I'm curious to know since I seem to have a similar issue with my fuel gauge.