What is a probable cause for low compression in multiple cylinders when values are closely similar but below normal levels?

Low compression in multiple cylinders with closely similar but below-normal levels typically indicates a systemic issue affecting all cylinders. Worn piston rings is a likely cause because they create a seal between the piston and the cylinder wall. If the rings are worn, they cannot maintain proper compression, leading to reduced pressure levels across multiple cylinders.

When the compression readings are similar, it suggests that the problem is not isolated to a single cylinder, which supports the idea of worn piston rings affecting the entire engine's performance rather than a localized issue that might cause more variability in readings. This condition can lead to a decrease in engine power and efficiency, as well as increased emissions.

Other options, such as faulty fuel injectors, clogged air filters, or a damaged camshaft, could contribute to poor engine performance, but they tend not to cause uniformly low compression across multiple cylinders. These issues usually result in erratic compression readings or problems specific to individual cylinders rather than affecting all cylinders similarly.