Next

Step 5

Check center electrode C for signs of abnormal discharge, measure the gap between the center electrodes.

(a)

Check whether the spark plug torque is correct, the spark
plug tightening torqueis the 20-30Nm (14.8-22.2lb-ft). If the
torque is not adequate, the spark plug will not work correctly.
It the torque is too large, it may lead to insulator B cracking.

(b)

Check for signs of leakage around the insulator tip rather than
near the center electrode D.

(c)

Check for the electrode C-side fracture and worn.

(d)

Check whether the spark plug is broken, worn or loose by
shaking center electrode D. If a popping sound is heard, it
indicates the internal parts have been damaged. If the center
electrode spark D is loose, the spark plug intensity will be
reduced .

(e)

Check whether electrodes C and D are shorted. If it is the
case, the residue on the electrode C will reduce or even the
gap will disappear.

(f)

Check whether the electrode is too dirty.

Next

Step 6

Check the cylinder head slot for debris, otherwise it may damage the spark plug during the installation.

2.10.7.7 Common Spark Plug Malfunction

Serious Spark Plug Burn: Spark plug top scars, damage or electrode melting, brunt all indicate that the spark plug has been damaged
and should be replaced. Check the symptoms as well as color changes when replacing the spark plug, in order to analyze the
reasons for malfunction. Refer to 

2.10.8.4

 

Spark Plug Replacement

.

1. Electrode melting and the insulator turning white indicate that combustion chamber temperature is too high. This may be because

there is too much carbon residue in the combustion chamber, so that valve clearance is too small caused by overheating or
cooling malfunction. Another possible reason it that the spark plug tightening torque does not match the specified value.

2. Electrode  becomes  rounded  and  the  insulator  has  a  scar,  indicating  that  an  early  engine  combustion.  It  may  be  because

premature ignition timing, low-octane gasoline or spark plug too hot.

3. Insulator top is broken. Knock combustion is the main reason for the insulator rupture. Premature ignition timing, low-octane

gasoline or spark plug too hot may lead to engine knocking.

4. Insulator top has gray black strips, which indicate that the spark plug may have been leaking and should be replaced.

Spark Plug Residue: There is residue between the spark plug insulator top and the electrodes. In severe cases, it can cause the
engine inoperative. Cleaning the spark plug can be a temporary solution. In order to maintain good performance, identify the root
cause for the malfunction.

1. Oily Residue. Spark plug has oily residues, indicating that lubricating oil entering into the combustion chamber. If it only happens

to an individual spark plug, the valve rod seals may be damaged. If every cylinder spark plug has oily residue, it indicates that
there is cylinder channeling oil. Check whether the air filter and ventilation device is blocked.

2. Black Residue. There is black residue on the spark plug electrodes and inside the spark plug, indicating that the mixture is too

rich. Increase the engine running speed and continue for a few minutes to burn the layer of black soot on the electrode.

Engine

Ignition System JL4G18-D

2-531

1.

With normal spark plug, center electrode is gray or yellow.

FE02-2051b

2-532

Ignition System JL4G18-D

Engine

2.

With excessive fuel combustion, spark plug center electrode has serious corrosion.

FE02-2052b

Engine

Ignition System JL4G18-D

2-533

3.

With incorrect spark plug heat value or fuel system malfunction, the spark plug center electrode has excessive carbon residue.

FE02-2053b

2-534

Ignition System JL4G18-D

Engine