Difference between single-point and multi-point injection

While all modern cars use multipoint injection, many older cars (before the early 90s) benefit from singlepoint injection.

What's the difference and why?

Let's start from the beginning ... The first fuel system worked with a carburetor in which the fuel came out in the form of vapors mixed with air (the more you pressed the pedal, the more it opened. Alas, this process was not very successful. Then came injection (first single point ), which this time consisted of injecting the fuel (electronically controlled) directly into the intake manifold (or manifold), thus improving efficiency. choose for single-point injection.Finally, it was found that it would be even more economical to inject the fuel as close as possible to the combustion chamber, being able to control, cylinder, cylinder, dose sent: that is when multi-point injection appeared (direct or indirect: press see here for the Rens difference.) This multi-point injection was subsequently further developed into a system called "common rail" (click here to find out) or even a pump injector for Volkswagen (since abandoned).

The single point allowed fuel savings by very precise control of the amount of fuel delivered to the intake manifold (the carburetor does this a little more "coarsely"). Multi-point is just an evolution of the single-point as we apply the same process by integrating an injector into each cylinder (so production is more expensive...). This makes dosing even more precise, helping to prevent fuel wastage. Finally, a common rail (placed between the pump and injectors, acting as a pressure accumulator) further improved efficiency.

SINGLE-POINT injection: one injector delivers fuel to the manifold. The exhaust manifold is highlighted in red, but we are not particularly interested in it here.

MULTIPOINT injection: one injector per cylinder. This is a direct injection (I could also do an indirect injection to illustrate this: see the related article at the link given in the text above)

Explained by Wanu1966: Main Site Member

injection multipoint : Air is metered by a box placed in the intake manifold. The fuel is calibrated using a metering device, the damper of which is adjusted by moving an air flow meter located in the intake manifold. The fuel is supplied to the metering unit from the electric pump through the pressure regulator. The injectors continuously supply fuel, the pressure and flow rate of which is determined by the air flow rate and its absolute pressure.

Electronic injection single point : The term "single-point" means that there is only one injector in the system, as opposed to a multi-point system, which has one injector per cylinder.

Single-point injection consists of a throttle body located in front of the intake manifold (manifold) and on which the injector is mounted.

The air flow is measured by a potentiometer connected to the throttle valve and a pressure gauge mounted on the pipe. This information is transmitted to the computer, which signals engine speed, intake air temperature, oxygen content in exhaust gases and water temperature.

The computer analyzes this information and transmits a control voltage to the electromagnetic injector, the start, duration and end of the injection of which depend on the input parameters.

All comments and reactions

Dernier comment posted:

Mac Adam (Date: 2020, 06:07:23)

Hi,

Reading Suzuki's datasheet, I see that they indicate for two gasoline engines: multipoint injection for one and direct injection for the other. Finally, if I understood correctly, is it about the same thing? Thank you for the article.

Il I. 3 reaction (s) to this comment:

• Administrator SITE ADMINISTRATOR (2020-06-08 10:42:08): multi-point means multiple nozzles. So it can be direct or indirect.

  But by convention, we talk about multipoint when it is indirect (as opposed to monopoint), because with direct injection, it can only be multipoint.

  In short, multipoint = indirect with multiple injectors in the tube, and direct = direct ...

• GOSEKPA (2020-08-24 20:40:02): There is a contradiction in your letter.

  you say “” by convention, we talk about multi-point when it is indirect (as opposed to single-point) because with direct injection it can only be multi-point “.” Usually it is a straight line, which can only be multipoint.

• ABC (2021-06-08 23:31:01): I don't understand anything, what do you have at the end ??

(Your post will be visible under the comment after verification)

Write a comment

Are you sentimentally attached to yourself?