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Fuel Gauge System in Vanagon: How to Troubleshoot, Check, and Calibrate

This system consists of the following items:

Fuel gauge. If your gauge does not work at all, it could be a bad gauge—but they almost never fail, so that is probably not the issue.
Instrument cluster voltage regulator. If both your temperature and fuel gauges are on the blink, try this inexpensive fix first.
Instrument cluster printed circuit foil. If your fuel and/or temperature gauge work intermittently, or if they register way out of whack, you might need to replace this part.
Violet wire with black stripe from cluster to sending unit. This wire passes through the fuse box on 1986 and newer models. It almost never goes bad—but it's easy enough to do a continuity test between the cluster and the sending unit. There should be practically no resistance between the two points.
Brown ground wire from sending unit to chassis. Again, this almost never goes bad, but it's an easy continuity check, and should have close to zero resistance.
Sending unit in tank. This is often the culprit! A worn sender can cause the gauge not to read at all or inconsistently. For example, a common symptom caused by a worn sender is that the gauge will have a "dead zone," where it reads full when you fill the tank, then 50 miles later the gauge will read empty, then 100 miles after that it will read 1/3 tank. This is a classic worn sender symptom. 

TROUBLESHOOTING

The best way to check if everything in the system is working as it should—other than the sending unit—is to proceed as follows:
1. Unplug the sending unit.
2. Get behind the wheel, turn the ignition key to the run position, and watch the fuel gauge. The gauge needle should not move at all.
3. Install a jumper between the pins in the plug that goes on the sending unit (short the pins). A paperclip works well.
4. Get behind the wheel, turn the ignition key to the run position, and watch the fuel gauge. The gauge needle should go straight to fully pegged.

If it passes this test, the entire system is working fine—and you just have a bad sending unit in the fuel tank. Easy peasy!

CHECKING

Once you get the system functioning, you'll probably want to make sure it's actually reading accurately, right? Here are the steps to do just that:

1. Drain tank completely with the vehicle perfectly level. The easiest way to do this is to drive the vehicle until it is out of gas—but, of course, that can be hazardous. On gasoline vehicles, you can use the electric fuel pump, which is less convenient, but safer. Run the vehicle until it is very low on fuel, then drain out the rest using the electric fuel pump itself. On the fuel rail (on the engine) is a test port that is available for pressure tests; it is located very close to the distributor (see Bentley manual page 24.25). You can tap into that with a length of hose and run the other end into a clean container. Then hot wire the pump so that it runs continuously. This is easily done by removing the fuel pump relay (placement varies according to model) and running a jumper wire across where the outputs of the relay would normally jumper. Run the fuel pump until all the fuel is gone, and then put it all back together. 
2. Get behind the wheel, turn the ignition key to the run position, and watch the fuel gauge for a minimum of 2 minutes. The gauge should read right at the bottom of the red zone.
3. Add 2.5 gallons of fuel and watch the gauge for another 2 minutes. The fuel gauge should indicate right at the top of the red zone.
4. Go to the filling station and fill the tank completely. Gauge should read totally full. 2WD models should take an additional 13.5 gallons. Syncro (4WD) models should take an additional 16 gallons. SECRET "BET YOU DIDN'T KNOW THIS" NOTE: On Syncro (4WD) models, it takes quite a bit of effort to get the tank completely full. Rolling the right two wheels up on blocks makes filling to full quite a bit easier. You can actually get another 17.5 gallons in there (total of approximately 20 gallons), and the gauge will actually read above full.

If the gauge behaves as described above, the system is working as it should. "But wait," you said. "The gauge is still really inaccurate—I know by looking at my odometer that when it reads 1/2 tank, I really have something like 2/3 left!" This is normal; Vanagon gauges are what is referred to in engineering terms as "indication only" gauges. The fuel gauge is not linear and varies from vehicle to vehicle—and, of course, it varies even more if the vehicle is not level or is subject to G-loading, like when you're negotiating a turn. But what is most important is that A) the reading is consistently the same under the same conditions, and B) you know when you are 2.5 gallons from completely empty. If the gauge is working as it should, you can count on it to keep you out of trouble, which is its job. If the gauge does not behave as described above—but reads consistently under similar circumstances—you can just choose to live with it and make sure whomever drives is well-informed. If the gauge is not consistent, or you just really want it to work the way it was designed to work, you can calibrate the system.

Calibration requires removal of the fuel level sending unit. You might as well order a new one, because you really don't want to do this twice. Replacing the sending unit on a 2WD Vanagon requires dropping the fuel tank, so in addition to the new sending unit, you'll also need one of our fuel tank re-seal kits. On 4WD models, the work can be done with the tank in place; all you will need is a new Syncro fuel sending unit kit. Please refer to your Bentley manual for details about the removal and installation of the sending unit. The sending units are tested at the factory, and they are all made exactly the same, thus behaving identically. However, the position of the float (that floats on the top of the fuel) relative to the mounting plate (that fastens to the tank) is not exactly the same from one tank to the next. This is because the tanks are rather thin and flimsy. Small angular variations between tanks are to be expected. This is especially true in the case of 4WD models, where the fuel tank is plastic, and it's probably why the fuel gauges in Syncros are notoriously variable from one vehicle to the next. Thus, fuel sending units are in fact "plug and play." You can install one, and the gauge will read something—and it will read that same something consistently. But for those of us that really want to know how much fuel we have left when the needle is at the top of the red... well, calibrating the new sending unit for your particular fuel tank is the only way to go. NOTE: This is a very tedious iterative process—not recommended for the impatient!

CALIBRATION

1. Plug new fuel sending unit into the vehicle harness with the sending unit not installed in the tank. 
2. Set up sending unit so that the float lever is resting on the bottom stop tab (float all the way down, as when there is no fuel in the tank). 
3. Get behind the wheel, turn the ignition key to the run position, and watch the fuel gauge for at least 2 minutes. The gauge should read right at the bottom of the red zone.
4. If the gauge does not read at the bottom of the red zone, adjust the bottom tab on the sending unit until it does. NOTE: After every change, you need to sit and wait at least 2 minutes for the gauge to "settle." 
5. Flip sending unit upside down so the float is resting on the top tab (float all the way up as when the fuel tank is full). 
6. If the gauge does not read full, repeat steps 3 and 4 above. This time, though, adjust the other tab until the gauge reads full. 
7. Install the new sender in the tank and repeat step #3 above. Note: In order for the fuel sender float lever to rest against the bottom tab after installed with fuel tank empty, the float needs to in the flat position relative to the bottom of the fuel tank. This means that, upon installation, the float must be parallel with the sender fastening plate on 2WD, 90 degrees to the sender fastening plate on 4WD. You can use a little dab of heavy grease between the float and float arm to keep it in the correct position. The grease will dissolve in the fuel and not hurt anything. Once the sender is back in the empty fuel tank with the float in the correct position (so it does not obstruct the float arm from moving), the float arm should be up against the bottom stop tab of the sending unit. Therefore, the gauge should indicate in the exact same spot indicated with the sending unit back in the tank as when you checked it with the fuel sender out of the tank—if the float arm is resting on the bottom stop tab of the sending unit as it should in an empty tank. If the gauge reads as it should, skip to step 11. If it does not, that indicates the float lever is not moving all the way down and against the bottom tab on the fuel sender. This could mean the float itself is turned up on its side—so double check that. If you are sure the float is indeed flat, then the float must be hitting the bottom of the tank before the float arm can reach the stop tab. If so, proceed as follows:
8. Remove the sending unit from the fuel tank.
9. Bend the float arm very slightly so that the float is in a higher position with the float lever arm resting on the bottom stop. Note: The farther away from the float you make your bend, the more drastic the change will be. So, make your bend about an inch away from the float so you can better control how much of a change you are making. The goal is to move the float as little as possible so as to achieve float arm contact with the bottom stop tab simultaneously with the float sitting on the bottom of the tank (no fuel).
10. Repeat steps 7, 8, and 9 as needed.
11. Put in 2.5 gallons of gasoline. The fuel gauge should read right around the top of the red (reserve) zone. If it does, you are all set, and the gauge is now reliable. When it indicates you are at the top of reserve, you have about 2.5 gallons left—and you'd better find a filling station in the next 30 miles or so! If, on the other hand, the fuel gauge reads too low (needle in the red zone), that means the float arm is hitting the bottom stop tab before the float is resting on the tank floor with no fuel present, which means the first bit of fuel you put in the tank does not move the float at all, so the sender cannot register it. You bent the lever too far—time to go back to step 7!

We warned you that the calibration process was tedious!

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