1. Fuel Level Sending Unit:
* Location: This is a float-type device located inside the fuel tank. The float rises and falls with the fuel level, sending a resistance signal to the gauge. It's the most common failure point for gas gauges.
* Testing: This requires dropping the fuel tank (a significant job). Once you access it, you can check the float arm's movement and test the resistance of the sending unit with a multimeter. You'll need a wiring diagram for your specific van to know which wires to test and what resistance values to expect at different fuel levels. A bad sending unit will often show wildly inaccurate or fluctuating resistance.
* Repair/Replacement: Replace the sending unit if it's faulty.
2. Wiring and Connections:
* Corrosion/Breaks: Examine the wiring harness leading from the sending unit to the instrument cluster. Look for broken wires, corrosion at the connections (especially where they enter the tank), or chafing. A short circuit or a broken wire could easily cause the needle to peg.
* Testing: Use a multimeter to check continuity and voltage in the wiring. Again, a wiring diagram will be crucial. You might need to disconnect the sending unit harness at both ends to test the entire wire path for continuity.
* Repair: Repair or replace any damaged wiring. Clean corroded connections.
3. Instrument Cluster Gauge:
* Less Likely: While possible, it's less likely that the gauge itself is the problem if the needle is pegged consistently past full. If the sending unit and wiring are okay, the gauge might be internally shorted, but other symptoms (like erratic needle movement, or the gauge not working at all) are usually associated with gauge failure.
* Testing: This requires expertise, often involving removing the instrument cluster and testing its internal components. It's the most involved repair.
* Repair/Replacement: Replace the instrument cluster. However, before proceeding to this stage, ensure you've checked the first two points above.
Before you start:
* Safety First: Work in a well-ventilated area when dealing with fuel. Disconnect the negative battery terminal before working on any electrical components.
* Wiring Diagram: Obtain a wiring diagram for your specific 1992 Chevy G20 van. This is essential for proper testing and repair. You can often find these online through repair manuals or online forums dedicated to Chevy vans.
Recommendation:
Start with visually inspecting the wiring. If that's okay, the fuel sending unit is the next most likely suspect. Replacing the sending unit is a lot less work than replacing the instrument cluster. Only move to testing the instrument cluster as a last resort. If you're not comfortable working on automotive electrical systems, it is best to take the van to a qualified mechanic.
