Compression (Dynamic)

General Information:
The compression test is performed over the starter current draw. The decompression cycle is measured to indicate the mechanical condition of the engine. This data will provide indirect information about engine timing, frictional horsepower and compression via data tables and scope patterns.


Prerequisites:
- Engine OFF.
- Attach current clamps to battery negative (B-) terminal (on model 129, ground connection between transmission and chassis [accessible from underneath only] on right hand side; on model 140/202, left hand side).
- Wait for additional instructions to appear.
- Start engine.
- Engine at idle until further instructions.
- Display: "Print display or diagram".

Bad Scope Pattern:

OT Top dead center (TDC)
Cylinder 4 Cylinder with low starter current (bad compression)
ISS Starter current in Ampere Measurement value
ms Time in milliseconds


4-Cylinder engine, Engine 102/111:





The largest and smallest cylinder values, as well as the difference of these values, are given when printing the current table.

This will make the evaluation of the magnitude of the failure easier. The value listed under difference can be used to determine if a mechanical failure is present, for example: difference of ISS > 4A on 4-cylinder engines means that there is possibly a mechanical failure present.

See section "Test and Adjustment Data". Test and Adjustment Data [Specifications]

Compression Scope Pattern, Engine 102/111:

Good scope pattern.
The relation of the curve to the cylinders is determined by the entered firing sequence
1 - 3 - 4 - 2, starting with cylinder 1.


6-Cylinder engine, Engine 103, 104:





The relation of the curve to the cylinders is determined by the entered firing sequence 1 - 5 - 3 - 6 - 2 - 4, starting with cylinder 1.

See "Test and Adjustment Data". Test and Adjustment Data [Specifications]

Compression Scope Pattern, Engine 103, 104:

Good scope pattern shown

Compression Scope Pattern, Engine 103, 104:

Bad scope pattern
- Low starter current on cylinder 3, bad compression.


8-Cylinder engine, Engine 116, 117:





See "Test and Adjustment Data". Test and Adjustment Data [Specifications]





On 8-cylinder engines, the average current value between the cylinder banks is compared and the difference shown. This allows identification of engine timing failures.

See "Test and Adjustment Data". Test and Adjustment Data [Specifications]

8-Cylinder Engine Scope Pattern (Good), Part 1:

8-Cylinder Engine Scope Pattern (Good), Part 2:

The relation of the curve to the cylinders is determined by the entered firing sequence 1-5-4-8-6-3-7-2, starting with cylinder 1.

NOTE: On 8-cylinder engines, the scope pattern is continued in image "8-Cylinder Engine Scope Pattern (Good), Part 2" of the engine analyzer with cylinders 7 and 2.

8-Cylinder Engine Scope Pattern (Bad), Part 1:

8-Cylinder Engine Scope Pattern (Bad), Part 2:

Low starter current on cylinder 2, bad compression.

NOTE: On 8-cylinder engines, the scope pattern is continued in image "8-Cylinder Engine Scope Pattern (Bad), Part 2".


12-Cylinder engine, Engine 120:
On 12-cylinder engines, the average current value between the cylinder banks is compared and the difference shown below. This allows identification of engine timing failures.









See "Test and Adjustment Data". Test and Adjustment Data [Specifications]

12-Cylinder Engine Scope Pattern (Good), Part 1:

12-Cylinder Engine Scope Pattern (Good), Part 2:

Good scope patterns shown.
The relation of the curve to the cylinders is determined by the firing sequence 1-12-5-8-3-10-6-7-2-11-4-9, starting with cylinder 1.

NOTE: On 12-cylinder engines, the scope pattern is continued in image "12-Cylinder Engine Scope Pattern (Good), Part 2" of the engine analyzer with cylinders 7 and 2.