GMC Powertrain 4.3 L, Руководство по обслуживанию, Страница: 21 / 196

Engine Marine/Industrial 4.3L 6-11
2000 Marine/Industrial
Base Engine Misfire Diagnosis (cont’d)
Checks Action
Abnormal Internal Engine Noises 1. Start the engine and determine if the noise is timed to the engine camshaft speed or
the crankshaft speed.
2. Using a timing light, two knocks per flash is the crankshaft speed and one knock
per flash is the engine camshaft speed.
3. If the noise is timed to the engine camshaft speed, inspect the following:
Missing or loose valve train components
Worn or loose valve rocker arms
Worn or bent valve pushrods
Faulty valve springs
Bent or burnt valves
Worn engine camshaft lobes
Worn or damaged camshaft timing chain and/or sprockets
Important: A slight COLD knock or piston slapping noise could be considered normal
if not present after the engine has reached normal operating temperatures.
If the knock is timed to the crankshaft speed, inspect the following:
Worn crankshaft or connecting rod bearings
Piston ro cylinder damage
Worn piston or piston pin
Faulty connecting rod
Excessive carbon build-up on the top of the piston
No Abnormal Internal Engine Noise 1. Inspect for a worn or improperly installed camshaft timing chain and/or sprockets.
2. Remove the valve rocker arm cover on the side of the engine with the cylinder that
is misfiring.
3. Inspect for the following:
Loose valve rocker arm studs
Bent valve push rods
Faulty valve springs
Faulty valve lifters (bleeding down)
Worn or improperly seated valves
Worn engine camshaft lobes
Engine Compression Test
1. Disconnect the positive ignition coil wire plug from
ignition coil.
2. Disconnect the fuel injector electrical connector.
3. Remove all the spark plugs.
4. Block the throttle plate wide open.
5. Charge the battery if the battery is not fully
charged.
6. Start with the compression gauge at zero. Then
crank the engine through four compression
strokes (four puffs).
7. Make the compression check the same for each
cylinder. Record the reading.
The minimum compression in any one cylinder
should not be less than 70 percent of the highest
cylinder. No cylinder should read less than 690
kPa (100 psi). For example, if the highest
pressure in any one cylinder is 1035 kPa (150
psi), the lowest allowable pressure for any other
cylinder would be 725 kPa (105 psi).
(1035 x 70% = 725) (150 x 70% = 105).
8. If some cylinders have low compression, inject
approximately 15 ml (one tablespoon) of engine
oil into the combustion chamber through the spark
plug
hole.
• Normal - Compression builds up quickly and
evenly to the specified compression for each
cylinder.
• Piston Rings Leaking - Compression is low on the
first stroke. Then compression builds up with the
following strokes but does not reach normal.
Compression improves considerably when you
add oil.
• Valves Leaking - Compression is low on the first
stroke. Compression usually does not build up on
the following strokes. Compression does not
improve much when you add oil.
• If two adjacent cylinders have lower than normal
compression, and injecting oil into the cylinders
does not increase the compression, the cause
may be a head gasket leaking between the two
cylinders.
9. Install the removed parts.
10. Connect the disconnected components.