The econometer's design was surprisingly simple. Essentially, it was a regular mechanical vacuum gauge with no electronic components.
A thin hose connected to the device led to the intake manifold of the carbureted engine. The needle on the dashboard moved based on changes in vacuum within the manifold.
The operating principle was based on natural processes inside the engine. When the pistons moved down, they drew in the fuel-air mixture through the partially closed throttle valve. Below the valve, a pressure lower than atmospheric was created, and the device registered this difference. The more the valve was closed, the higher the vacuum became.
If the driver drove calmly and didn't press the accelerator pedal, the throttle remained partially closed, the vacuum stayed high, and little fuel entered the cylinders. In this mode, the needle was in the green zone. With a sharp press of the pedal, the throttle opened almost completely, the vacuum disappeared, the mixture supply increased, and the needle moved into the red sector. Thus, the econometer displayed not fuel consumption in liters, but the degree of opening of a peculiar "tap" for mixture supply.
Why the scale had no numbers
The developers deliberately opted out of numerical designations. Instead, three color zones were used: green, yellow, and red.
This solution allowed the driver to instantly perceive information. There was no need to scrutinize readings and be distracted from the road to assess the needle's position.
When idling or driving at a steady pace, the needle was usually in the green sector. As soon as acceleration became more active, it moved into the yellow area. Uphill driving or intense acceleration almost always pushed it into the red zone.
In practice, this looked like this:
- in the green sector, the VAZ-2107 consumed approximately 6–8 liters per 100 km;
- in the yellow, consumption increased to 9–10 liters;
- in the red, it could approach 14 liters per 100 km.
When the throttle was fully open, the vacuum decreased so much that a special valve for additional mixture enrichment began to operate in the carburetor. Therefore, in the red zone, the engine not only consumed more air but also received an increased portion of gasoline.
How drivers used the econometer
The main thing this device taught was careful use of the accelerator pedal. It literally showed the cost of each sharp acceleration.
Economical driving implied:
- smooth start without sharp pedal presses;
- early release of the accelerator before intersections and turns;
- avoidance of constant accelerations and decelerations.
In addition, the econometer helped choose the correct gear. At the same speed, a higher gear provided lower engine RPMs, which meant the needle more often stayed in the green zone. When driving in a lower gear, the engine ran louder, and fuel consumption increased.
If the needle could be kept predominantly in the economical sector, fuel consumption on the "semerka" decreased by approximately 1.5 liters per hundred kilometers. Over a month of operation, this resulted in quite tangible savings.
The needle's deviation towards maximum economy was especially noticeable during engine braking. When the car was moving downhill or approaching a traffic light in gear with the accelerator pedal released, the throttle remained closed, and the vacuum reached its maximum. At this moment, the EPHH system cut off fuel supply through the idle circuit until engine RPMs decreased.
In fact, the car continued to move with almost no fuel consumption. When coasting in neutral, this effect did not occur, as the engine continued to idle and consume gasoline.
Free engine diagnostics
The econometer proved useful not only for monitoring fuel consumption. Many mechanics used it as an additional diagnostic tool.
On a fully warmed-up, properly functioning engine, the needle should remain stationary at idle.
Deviations could indicate various malfunctions:
- chaotic fluctuations indicated air leaks through a damaged hose or a non-hermetic gasket;
- a stable position of the needle below the usual level could indicate late ignition or engine wear;
- periodic rhythmic dips often pointed to a burnt valve or a breach of its sealing;
- fine, frequent vibration combined with smoke from the exhaust pipe often accompanied worn valve guides.
Additional information was provided by observing the needle at higher RPMs. If its position gradually shifted downwards, the cause could be a clogged exhaust system or worn piston rings, which made it harder for the engine to expel exhaust gases.
Experienced specialists, based solely on the needle's behavior, could significantly narrow down the range of possible malfunctions even before disassembling the engine.
Automotive press of that time regularly published recommendations for diagnostics using an econometer. The device could indirectly even indicate insufficient tire pressure. When the wheels were underinflated, rolling resistance increased, engine load increased, and the needle more often shifted towards the red zone during normal driving.
To exclude sharp fluctuations caused by each engine cycle, a small damping jet was installed in the fitting or hose. This element often became the cause of failures. Usually, the device itself did not break: the jet or the channel in the intake manifold became clogged. In many cases, the needle could be brought back to life with a regular sewing needle.
A damaged hose created another problem – an additional air leak. This led to a lean mixture and unstable engine operation.
Eco-mode long before onboard computers
Similar devices appeared much earlier than the VAZ-2107. In American cars, vacuum gauges were used as early as the 1960s, and after the 1970s fuel crisis, they gained additional popularity.
Various versions of such systems were used by:
- General Motors with Econominder devices;
- Chrysler with Fuel Pacer indicators;
- Mercedes-Benz;
- BMW.
Chrysler, instead of a needle, could use a special lamp that lit up when the accelerator pedal was pressed excessively.
In essence, the econometer performed the functions of a modern economical driving mode. Today, trip computers provide similar information, displaying instantaneous fuel consumption and various environmental indicators. The econometer solved the same problem approximately two decades before such electronic systems became common equipment in cars.
Why the econometer disappeared
For experienced motorists, the device gradually lost its relevance. They understood the engine load by its sound and the car's reaction to the accelerator pedal even without additional prompts.
Novices, on the other hand, were often too busy driving to constantly monitor an additional needle on the dashboard.
The econometer also lacked accuracy. It only registered the vacuum level in the intake tract, not actual fuel consumption. During accelerations and decelerations, readings could noticeably differ from the actual picture. Moreover, the desire to keep the needle in the green zone at all costs was not always beneficial. For example, when driving in a high gear at low RPMs, the needle might show increased load, although actual fuel consumption remained low.
The final fate of the device was decided by the transition to fuel injection systems. With the advent of fuel-injected engines and trip computers capable of displaying accurate instantaneous and average consumption, the need to measure vacuum in the intake manifold disappeared. While the econometer still had practical meaning on carbureted "Zhiguli" cars, it became virtually useless on fuel-injected versions.
Interestingly, this device did not appear immediately on the VAZ-2107. Cars of the first years of production, starting from 1982, were equipped with an oil pressure gauge located in the upper left corner of the dashboard. Only in 1988 did the factory abandon it and install the econometer in its place.