Chasing the Noise

Oct. 18, 2019

Owners of 2017-2019 GM vehicles, such as GMC Canyon and Acadia vehicles equipped with a 3.6L engine, may complain about a rattle, tick or knock type noise.

This may also be accompanied by DTC P0300, P0302 or P0305 on the active fuel management system (AFM) cylinders. This also applies to Buick LaCrosse and Regal, Cadillac ATS/CT6/CTS and XT5, Chevy Camaro and Colorado vehicles with the 3.6L engine.

This condition may be caused by spongy stationary hydraulic lash adjusters (SHLAs) or damaged switching roller finger followers (SRFF) or a left bank timing chain tensioner gasket not sealing. This condition could be constant, only under load, intermittent or when first started after a hot soak.

1. Perform injector diagnosis to ensure that there are no leaking injectors causing a noise due to excessive fuel in one cylinder.

2. Perform cylinder cancellation for each cylinder. This may help pinpoint the source of a rattle noise.

3. Remove the intake manifold and visually inspect for excessive carbon on the intake valve stems and the top of the valve. If carbon is present, clean the valves or replace the heads as needed and re-evaluate the concern.

4. Remove the cam cover of the affected bank (or both) to isolate and inspect for soft, spongy or damaged SHLAs or rockers on all cylinders. Push down on the rocker end at the SHLA to test for a soft or spongy feel. Check for any visible damage to non-AFM rocker clips. If soft/spongy or damaged SHLAs or rockers are found on either intake or exhaust side of any cylinder, it will ne necessary to replace all of the affected cylinder SHLAs or rockers and re-test.

5. If the replacement SHLAs are still spongy, it will be necessary to remove the affected cylinder head and inspect the head gasket for debris in the oil passages. If debris is found, inspect the camshaft caps for wear or discoloration due to lack of oil. If wear or discoloration is found, replace the cylinder head assembly and camshafts. If there is no wear or discoloration, clean the oil passages and replace the head gasket. Change the engine oil and filter and re-evaluate the concern.

6. Without starting the engine, crank the engine over and ensure that the valves are opening and closing. If they are not operating correctly, it will ne necessary to inspect the SRFF for any damage. Camshaft carrier assembly removal will be necessary to fully inspect the rockers and SRFFs. If any one of the SRFFs are damaged, it will be necessary to replace all four on the affected cylinder.

7. Inspect the left bank timing chain tensioner gasket to determine if it is leaking. Replace the tensioner and gasket if a leak is found.

8. If the noise is still present, raise the vehicle while running, with an assistant inside. With chassis ears or a stethoscope, listen to the right and left sides of the engine. Once the noise is isolated or if unable to isolate, remove the piston and rod assemblies from the affected bank(s) to inspect for either a loose rod bushing in the rod or loose wrist pin. Note: there should be no metal found in the oil for this condition. If a loose rod bushing or loose wrist pin is found, replace the piston and rod assembly.