Cold engine start accelerator (Audi 80 B4)

The cold start accelerator is sometimes compared to the choke control handle. However, this is not true. Although you have to pull the accelerator handle when starting a cold engine, this advances the fuel injection, not closes the choke valve. The accelerator ensures better engine starting and, in addition, the engine picks up speed faster during the warm-up phase immediately after starting. Starting the engine with the accelerator pulled out does not cause dark blue exhaust emissions, which usually suggests engine failure.

The accelerator must be pulled out when starting a cold engine, regardless of the ambient temperature. Only in severe frost can the engine sometimes be started faster if the accelerator handle is not pulled out.

After about a minute, the accelerator handle should be returned to its original position. However, if this does not happen, the engine will not be damaged. The starting accelerator performs the same function as the fuel injection advance clutch. Through the corresponding lever, the accelerator rod acts on the ignition advance clutch piston, moving it back. This causes an advance displacement of the pusher roller by about 2.5°.

Pulling the cold start accelerator handle also slightly increases the idle speed. The combination of these two functions is specially implemented to avoid shaking of the power unit, which is typical for diesel engines when running in a cold state. The cold start accelerator handle can be pulled out a little if there is a need to slightly increase the engine speed individually.

In vehicles with air conditioning, the idle speed increase device prevents the idle speed from dropping when the air conditioning compressor is switched on. At this point, the membrane-type vacuum regulator moves the fuel injection pump control lever in the "Full throttle" direction. In vehicles manufactured before 1/92, the vacuum regulator is controlled by the idle speed increase relay, located under No.13 on the additional relay block on the left under the instrument panel. Starting from 2/92, this relay is a component of the EGR control unit. Due to the increased size of the block, it is located at locations 13 and 14 of the additional relay block.

The fuel injection pump is equipped with a shock absorber of vibrations of the power unit, preventing its increasing tension when the accelerator pedal is pressed sharply. The need for such a shock absorber is dictated by the very "soft" suspension of the power unit. The shock absorber has a programmed backlash, providing the engine with the ability to lean on the necessary support when pressing the accelerator pedal before the engine speed corresponds to the full load. As a result, the swinging of the power unit on the suspension supports is eliminated.

The vibration damper is supplemented with a so-called locking damper, which prevents the power unit from swinging when the accelerator pedal is released abruptly. For this purpose, a small damper is installed on the injection pump control shaft, which dampens the speed of the lever movement caused by a sharp drop in the tension of the accelerator cable, and only then moves the lever (see illustration 3.0).