Fuel Gauge: Difference between revisions
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In addition to the fuel gauge, there is a low fuel warning light, operated by a separate rheostat and low fuel switch (on a different circuit). | In addition to the fuel gauge, there is a low fuel warning light, operated by a separate rheostat and low fuel switch (on a different circuit). | ||
Revision as of 14:04, 9 May 2022
Overview of the VR4 Fuel Gauge
The fuel gauge in the VR4 is an analogue gauge whose signal and reading is based on changing resistence of two rheostats (fuel senders) located in the fuel tank. The gauge itself is measuring current flowing through the gauge, with the amount of current changing based on the combined resistance of the two fuel senders.
The fuel gauge is notoriously inaccurate due to the design of the fuel tank shape and the lack of any computer controlled calibration of the gauge reading against the witnessed changes in resistance.
In addition to the fuel gauge, there is a low fuel warning light, operated by a separate rheostat and low fuel switch (on a different circuit).
Fuel gauge circuit
The diagram below (taken from the VR4 electrical wiring diagram workshop manual) shows the circuit path between the Fuel gauge and the fuel level senders. The sensors are wired in series with the upper (sub) sender altering its resistance first before bottoming out around the same time that the lower (primary) sender also begins to drop.
Fuel gauge inaccuracy
Without any modifications installed to resolve the issue, the fuel gauge is known to be highly inaccurate. The reasons for Mitsubishi not putting in the time and effort to make an accurate gauge are unknown, but the community consensus is that the gauge and sender setup are a "parts bin special" using components from the Mitsubishi Lancer Evolution.
Reasons for fuel gauge inaccuracy
By virtue of not using any form of gauge calibration, the inaccuracy of the fuel gauge is primarily caused by the design and shape of the fuel tank. The VR4, like the Lancer Evolution, uses a saddle-tank fuel tank design where the lower middle of the fuel tank needed to be shaped to fit over the driveshaft.
As a result of the saddle tank design, the fuel gauge is only accurate for about the first 20 litres of consumed fuel. At this point, fuel is located in both the driver and passenger sides of the fuel tank, with the "saddle" keeping them separate. The venturi jet located on the passenger side of the fuel tank will cause fuel to be lifted and pumped back over to the driver's side, but fuel can also "slosh" back over to the passenger side during right turns.
Given the saddle tank design and the act of fuel constantly sloshing back and forth over the saddle, an accurate fuel gauge required better calibration which Mitsubishi chose not to implement.