KMS MP25 - Start-Up; Throttle Pump Effect

KMS MP25(M)/MA25(M) manual Version 4.2
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3.2.4.1.4 Start-up
When the engine is started, a certain quantity of extra fuel
(in most cases dependent on the coolant temperature) will
have to be injected to ensure proper firing of the engine.
There is a possibility of giving a start-up injection impulse
and start-up enrichment. The start-up injection impulse is
given once, at the moment the first crankshaft signal is
registered.
After the start-up injection impulse, the injection periods
shown in the injection graph will be adhered to. As long as
the engine speed is lower than 500 rpm, the quantity of
injected fuel shown in the first row applies. Proper firing of
the engine often requires more fuel (depending on coolant
temperature) than the quantity needed when the engine is
already running at the same engine speed. This extra
enrichment can be entered in the table for the duration of
a certain amount of crankshaft rotations. There are four
coolant temperature ranges for which an enrichment table can be completed. The additional
enrichment (%) in the table can be set during the input of the rpm range. An enrichment map and a
startup-pulse can be filled in for four coolant temperature ranges. Above the highest temperature
the normal startup pulse will be used.
3.2.4.1.5 Throttle pump effect
When the throttle valve is opened, the engine will draw in
more air and therefore need more fuel to keep the mix
ratio at a constant level. As air is a gaseous substance, it
will reach the inlet valve earlier than the liquid fuel, which
because of its higher inertia needs more time to
accelerate. As a result, there will briefly be a weak mix,
causing the engine to 'hesitate'. The faster the throttle
valve is opened, the greater this effect will be. To
neutralise the effect of fuel having a higher inertia than
air, acceleration enrichment can be applied. This means
that, depending on the throttle valve opening speed, extra
fuel is injected. This prevents the formation of a poor
mixture.
There are two types of acceleration enrichment (these can
be set on/off separately). We recommend to use ‘Type 2’
acceleration enrichment.
Type 1:
The quantity of extra fuel to be injected can be set for the
three engine speed ranges indicated. The duration of
enrichment can be set by entering the number of
crankshaft rotations. The acceleration enrichment will
automatically decrease at lower throttle valve opening
speeds. Acceleration enrichment type 1 is always linked to
‘Engine load 1’.