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Question: When diagnosing a misfire in a four-cylinder engine the technician performs a compression test and finds cylinder #2 only has 70 psi when the specification is 165 psi. A cylinder leakage test measures 8% leakage. What is the most likely cause of this concern?
Answer: A worn intake camshaft lobe, faulty lifter or out of adjustment intake valve
A compression test measures the pressure in a cylinder caused by compressing the air brought into the cylinder during the intake stroke. A cylinder leakage test measures the percentage of air that is lost inside the combustion chamber with both valves closed and the piston at the top dead center of the compression stroke. An 8% loss in pressure is normal for an engine, as a small amount of air will be lost past the piston rings. Normal leakage test results indicate that the combustion chamber is sealing properly and not the cause of the lower compression. An intake valve that does not open all the way, caused by a worn intake camshaft lobe, faulty lifter or out of adjustment intake valve would cause less air to enter the cylinder, which would result in lower-than-normal compression.
Congratulations to the following shop who answered this question and will be receiving a prize pack!
- Mike at Jake's Auto Service Ltd. in Georgetown, ON
- Allan at Titan Automotive in Regina, SK
TECH CHALLENGE PROMOTION REMINDER
The Tech Challenge question is published in our weekly eNewsletter with an online answer form. Fill out the form with the details of how you would perform the repair to be entered for the chance to win the prize pack. You can also submit a challenge for future Tech Challenges! A draw is conducted with all shops who answered the question correctly and one is selected as a winner for a prize pack.
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