Page 974 - Workshop Manual - Tunland (2017)

04-288 DIAGNOSTICS - ENGINE CONTROL SYSTEM

04 sometimes explosion sound in the gas inlet manifold, and difficult cold car
starting etc..
(a) Carbon accumulates in the air throttle and combustion chamber.
If the engine burns the diesel oil, or impurity which the fuel of low quality contains is
too much, then it is more serious that the valve accumulates carbons and the forming
speed is faster.

Because the structure of the accumulated carbon is similar to the sponge, a part of
the fuel of each time sprayed into the cylinder is absorbed after the accumulated carbon
is formed, making the mixing gas thinner which enter into the cylinder, which may lead
to such abnormal phenomena as bad engine operation, difficult starting, unstable
idling, bad acceleration, emergency refuel backfire, and cheering such anomalies as
the flash back, exhaust exceed standard, exhaust gas exceeding the standard,
increased fuel consumption etc.. Serious situation can cause that the air inlet valve
can’t be closed tightly, individual cylinder cannot work completely due to no pressure
or even that the air inlet valve is adhered and can’t restore. The air inlet valve and
piston will produce the movement interference at this moment, and damage the engine
finally.
(b) Carbon accumulates on the air intake pipe.

Because each piston of the whole engine does not work simultaneously, when the
engine goes out, the air inlet valve of some cylinders can't be totally closed, some
unburned fuel is continuously to vaporize and be oxidized, some softer black carbon
will be produced in the air intake pipe, especially in the rear part of the air throttle.
On one hand, these accumulated carbon can make tube wall of intake pipe coarser,
where the air intake will produce vortex , influencing air intake efficiency and the quality
of mixing gas.

On the other hand, these accumulated carbon will also block idling path, making idling
control unit catching or beyond their adjustment range, such case will cause low idling
speed and idling quiver.
5 . Methods to judge accumulated carbon in the cylinder:
(a) Use an inner sight glass to observe the inside condition of the cylinder.
(b) Disassembly method.

CAUTION

If there is too much accumulated carbon in the engine cylinder, cylinder pressure will
get higher. But vehicles which have more accumulated carbon often have longer travel
mileage, cylinder pressure will drop due to abrasion. So it is not feasible to judge
accumulated carbon in the cylinder through cylinder pressure.

6 . To the danger of the accumulated carbon, the following several points should
be paid attention to:
(a) Refill high-quality diesel oil.
(b) Not to run at idling for a long time.
(c) Run at high speed as possible, try hard to improve the rotational speed of shift gears
of the manually shifting vehicles.