So I have a 76' maverick, and the fuel gauge always read as 1/4 tank as empty. So I ordered a new sending unit thinking maybe that was the culprit...not so. It still reads the same. Soooooo...what could be the problem? I have ran a separate grounding wire to the tank just to make sure...no change. Wiring from tank unit to gauge all good. So is it the regulator? The gauge? Do I need new glasses? Any help would be greatly appreciated!!
Just to help the question along - with the key off does the guage fall well below the empty mark? If so, does it do the same when the key is on and the sending unit wire is disconnected from the sender? (leave it hanging - do not ground it out)
Yes, with the key off it does fall back below empty like it should. But when the key is turned on it immediately goes up to 1/4. I tested it with the unit in the tank AND out and it did the exact same thing both ways.
Is your fuel tank pushed up on the bottom? Seems you would have seen this, but you never know! Are you sure you have the correct sending unit? That could be the issue. Also the floats are different for different years. I can't imagine the float being large enough to cause your problem, but I have seen some that are oblong and maybe it got turned so it lays on the bottom of the tank. I know this is all hit and miss, but I just can't think of anything else!
Could the voltage regulator on the instrument circuit board be not putting out enough volts or maybe a corroded connection somewhere? A tiny bit of conducting grease on old connectors can avoid voltage drops at the connectors. I'd test the voltage regulator and grease the connections before replacing the gauge.
Tank isn't bent at all. Sending unit is correct. I'm thinking the circuit board as well. I'll pull it out soon and check everything. In case it is the voltage regulator, where would I get the replacement?
I would be more concerned that it there is too much voltage. The fuel gauge is essentially a voltage meter reading across a simple linear proportional voltage divider. One 1 side of the divider you have the fuel level sense stuff, and on the other side you have the circuit board voltage regulator. AT E the Voltage should read closer to 0 and at F it should read closer to 5 or 6, I don't recall off the top of my head. Typically if the problem is from the sender, you get a low reading on the fuel gauge, and if it's the VR you get a high reading. So I agree with Jsarnold and you should try cleaning up or replacing the VR on the circuit board. My '71 would never get below 1/4 tank as well, I cleaned up the circuit board and the VR and all was right with the world. The other thing I want to point out is that in these cars the fuel gauge is also a direct window into the health of the overall charging system. If you have a bad alternator or regulator it can also affect the reading of your fuel gauge. Because of the way voltage regulators work you should also inspect to make sure you aren't putting 17 or 18 or more volts into your charging system.
I put in a new OEM replacement alternator this year when the old one bit the dust. I'll double check and see what it is putting out.
You're right, of course. Thanks for the correction. I'm having the same issue with my F100 with a new sending unit and new aftermarket gauge (no VR). Was thinking about that one wrong too. I may try adding a resistor in series to get it close. If it's fairly accurate on "E" it'll be OK.
If you put in a new replacement OEM regulator at the same time I would very much be checking on that, as I have gone through 5 of them in a year before. Yep, aftermarket stuff can be annoying to get sync'd up. A series resistor is often all the answer you need.
I'm not terribly 'electric' savvy. Are you referring to putting a resistor in-line with the sending unit to the gauge itself? And what size (s) would one use?
that is not the solution you want. He is trying to get aftermarket parts working, you are trying to get stock parts working. Often aftermarket parts are designed to be "close" in as many cars as possible and need a little help to be "right". Also the size is determined by the voltage drop you need to get, which means you need to take measurements to find out where you are, in order to get where you need to be. It's all just manipulations of P=IE.
