ASE A1 Engine RepairGeneral Engine DiagnosisMedium
A technician is performing a cylinder balance test using a scan tool. The engine is running at idle. When Cylinder 4 is momentarily disabled, the engine RPM drops significantly. When Cylinder 1 is disabled, there is almost no change in engine RPM. What does this indicate about Cylinder 1?
- ACylinder 1 has a significant contribution to engine power.
- BCylinder 1 is not contributing effectively to engine power.
- CCylinder 1 is running too rich.
- DCylinder 1 has a vacuum leak.
Show answer & explanationAnswer & explanation
Correct answer: B. Cylinder 1 is not contributing effectively to engine power.
If disabling a cylinder causes little to no change in engine RPM, it means that cylinder was already producing minimal power, indicating it is not contributing effectively.
Why the other options are wrong
- A. If Cylinder 1 had significant contribution, disabling it would cause a noticeable drop in RPM, similar to Cylinder 4.
- C. A rich condition might cause some power loss, but the primary indicator of non-contribution is the lack of RPM drop when disabled.
- D. A vacuum leak would typically cause a lean condition and a misfire, which would be reflected in the power output, but the direct interpretation of the balance test is about power contribution.
Cylinder Balance Test Interpretation
A cylinder balance test assesses each cylinder's power contribution. A significant RPM drop when disabled indicates a healthy cylinder; little to no drop indicates a weak or dead cylinder.
- Identifies weak/dead cylinders
- RPM drop correlates to cylinder health
- Performed by disabling individual cylinders
Memory trick: No RPM drop? That cylinder's a flop!