Engine Performance
Work Example 17

WorkKey Level: 4
NATEF Automotive Tasks: I.A.9, VIII.A

A good engine will have a fairly even compression from cylinder to cylinder.  If the highest and lowest readings vary more than 25% of the highest reading, the engine should be repaired. 

Compression readings for a 4-cylinder engine are shown below.  Determine if the engine compression range is within recommendations.

Cylinder 1	Cylinder 2	Cylinder 3	Cylinder 4
173	180	147	128

Which, if any, cylinder would you perform a cylinder leakage test on?  Please explain.

 

Solution:

The highest reading is 180.
25% of the highest reading = (.25)(180) = 45
The cylinders should be between (180 – 45) = 135 and 180.

You need to perform a cylinder test on cylinder 4 since 128 is less than 135.