Fuel gauge troubleshooting begins with isolating the problem either to the gauge or the sending unit. The majority of the time gauge problems are either a bad ground at the tank or a sender problem.
If a fuel gauge does not operate, is very slow to react or is inaccurate, there is a problem for sure. A fuel gauge that does not operate at all could suffer from four distinct problems. A fuel gauge needs to have an excellent ground to the frame at the gas tank-sending unit. This is usually the problem where the ground is loose or dirty causing too much resistance. That is the first place to start. If the ground is good, check for power at the sending unit. Pull off the electrical plug. Use a voltmeter to check for power (with the key on). If there is power and the ground is good, ground the terminal that had power momentarily. If the gauge operates, the sending unit in the fuel tank is inoperative and needs to be replaced.
If a fuel gauge is very slow to react, or is giving an inaccurate reading, the fault will lie with the sending unit with in the tank. Drain the fuel from the tank, remove the fuel tank and replace the sending unit. While in there, you should also replace the fuel pump. Often, the fuel pump and sender come as one unit.
The ground wire needs to be at least 16 gauge and secured on the frame rather than on the tank or body. This is not to say that a remote ground to other than the frame won't work, however, the odds are that it will not be as accurate without a direct path back to the battery.
When replacing a fuel sending unit, it is necessary to understand that all gauges and sending units are matched up as to the resistance that they require. For example a GM vehicle is usually a 90-ohm resistance fuel gauge and the same with the sender. If the wrong ohm range gauge or sender is inadvertently purchased, the gauge will not function at all.
Signs of a fuel gauge problem can present themselves without warning. Be prepared to act.
Before you get started with fuel pressure gauge repair, you should understand a few things about your fuel pressure gauge. Do you need two of them? Find out before you start working.