Ticking Sounds on Active Fuel Management Cylinders

A ticking or knocking sound may be heard on some 2016-2017 ATS, CT6, CTS, Camaro; 2017 LaCrosse, XT5, Colorado, Canyon and Acadia models equipped with the 3.6L engine (RPO LGX). The 3.6L engine uses Active Fuel Management (AFM) to conserve fuel. The ticking or knocking sound may be heard coming from the AFM cylinders. DTCs P0300 (Engine Misfire Detected), P0302 (Cylinder 2 Misfire Detected) or P0305 (Cylinder 5 Misfire Detected) may be set.

 

The ticking or knocking sound may be heard all the time, only under load, or intermittently. The sound may be caused by spongy stationary hydraulic lash adjusters (SHLA) (lifters) or a damaged switching roller finger followers (SRFF).

 

TIP: Prior to disassembly of any components, record a sound file or video with sound of the engine running. The file may be needed when contacting the Technical Assistance Center (TAC) or may be requested by GM Engineering.

 

Refer to #PIP5486 for diagnostic and repair instructions. The diagnostic steps must be performed in order.

 

Diagnosis includes verifying the injectors are not leaking and causing a noise due to excessive fuel in one cylinder as well as inspecting for excessive carbon on the intake valve stems and the top of the valve.

 

If the sound is still evident after these steps, test for soft or spongy stationary hydraulic lash adjusters (SHLA). (Fig. 11)

 

Fig. 11

 

It also may be necessary to inspect the switching roller finger followers (SRFF) for any damage, such as a stuck locking pin or fractured torsion spring. (Fig. 12) If any one of the SRFFs are damaged, replace all four on the affected cylinder.

 

Fig. 12

 

– Thanks to Aron Wilson

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