Case Analysis: Chevrolet Silverado

I was conducting diagnostic and repairs on a 2007 Chevrolet Silverado ZR1 6.0 Y pickup truck. One of my family members was complaining of a cylinder misfire on cylinders 1 and 6. My family member had already replaced plugs, wires, fuel injectors and coils associated with the cylinder and the cylinder misfire persisted. Once I was informed of this information I was instantly concerned of some form of internal engine failure. I will cover the series of events that happened during this repair to this 2007 Chevrolet Silverado.
I took on the repair even though I was inadequately prepared for the task. I lacked the proper diagnostic tools and knowledge to properly diagnose the problem that was troubling the vehicle. I needed compression gauges, cylinder leaked down tester, digital multimeter (DMM), valve train compression tools, micrometers, and feeler gauges just to name a few tools. Once I began conducting diagnosis of the vehicle I realized I would need some of these tools early on. First I began to rule out common issues to the cylinder misfires on cylinder 1 and 6. I began with a visual inspection of spark plugs and testing injectors and coils with a DMM and NOID light tester. Once I confirmed the issue was not being caused by fuel or ignition then came the trouble …show more content…
Chevrolet had released a Technical Service Bulletin (TSB) about this very issue. TSB PIP 4568S covered failure of the Active Fuel Management System (AFM) and cylinder misfires on 1,4,6,and 7. The AFM system relies on hydraulic pressure to cancel cylinders to conserve fuel which is controlled through Valve Lifter Oil Manifold (VLOM). The powertrain control module (PCM) controls the VLOM through groundside pulse width modulation and when driving condition are correct it uses solenoids within the VLOM to hydraulically cancel cylinders 1,4,6, and 7. These hydraulic lifters are prone to failure and damage internal engine