Low pressure
Uniformly low compression pressure is certainly not an alarm; the reason may be the difference in the measurements of different instruments. It is doubtful when the difference between the four measurements for the cylinders is more than 5 bar.
It means:
- Wear of pistons and piston rings.
- Piston rings rigidly seated due to precipitation.
- Cylinders are not round as a result of pinched pistons.
- Deposits on valve stems or valve seats due to combustion residues or engine oil.
- Broken valves.
Troubleshooting
In order to be able to localize the malfunction at low compression pressure, the following method is used: a little oil is poured into the nozzle hole and the pressure is measured again.
If the compression value remains bad again, then the valves are to blame.
If the pressure value rises, then the reason is in the piston rings and, perhaps, in the cylinders. A typical symptom of this malfunction is a slow rise in pressure when cranking the engine. The filled oil seals the gap between the piston and the cylinder wall for a short time, and compressed gases cannot escape through this gap.
Engine cranking
For some work, the crankshaft must be turned by hand. This is the easiest way to do it:
Raise the car on a jack, block it in front, turn on the fifth gear, turn the suspended wheel, from which the engine will also turn over.
If there is a sufficiently level place, push the car forward in fifth gear.
Or, with a 22 mm bent ring wrench, turn the central nut of the alternator pulley - turn the engine under the action of the belt.
Never turn the engine using the camshaft gear fixing bolt when the toothed belt cover is removed! The belt can slip teeth and the engine will deteriorate.
For various work on the engine and injection pump, it is necessary to set the piston of the first cylinder to the top dead center position (TDC), i.e. it should be at the top edge of the cylinder surface. For four-stroke engines (to which diesel belongs) During the working cycle, the piston is twice at TDC: once when compressing the intake air, and the second time when releasing exhaust gases. The position is usually used «ignition» after the compression stroke.
Positioning the first cylinder «ignition»
Remove valve cover.
Turn the engine over by hand until both right-hand camshaft lobes, visible in direction of travel, simultaneously point upwards.
At the same time, for greater accuracy, now turn the crankshaft so that the mark «FROM» on the flywheel was located opposite the arrow in the inspection hole of the clutch housing.
The TDC position has been reached.
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