Undercar: Diagnosing And Repairing Wheel Bearing Noise
2009-2014 GM Vehicles With Any of the Following Direct-Injected Gasoline Engines
- 2.0L (RPO LNF)
- 2.4L (RPO LAF, LEA, or LUK)
- 2.8L (RPO LAU)
- 3.0L (RPO LF1 or LFW)
- 3.6L (RPO LFX or LLT)
Some customers may complain of a MIL (malfunction indicator lamp, or check engine light) and engine misfire. In some cases, the misfire may be more apparent on a cold start, may count on a single cylinder or several cylinders, and may or may not be felt by the driver. Upon inspection, the technician will find one or more misfire codes (DTC P0300-P0306) stored in the ECM. Diagnostic steps in the service information may or may not isolate the cause of the misfire depending on whether the intake/exhaust valves are sticking at the time of the diagnosis.
This may be the result of major carbon build-up on the intake and/or exhaust valves as shown above; so, the misfires should not have appeared until accumulating at least 5,000 miles or more.
If this problem is encountered, perform a SI diagnosis. If the SI diagnosis isolates a valve-sealing concern and/or eliminates everything else external to the engine, decarbon the engine with upper engine and fuel injector cleaner by following the guidelines below.
Important: Extreme care must be taken not to hydro-lock the engine when inducing the cleaner, especially if it is induced without the correct tool. If too much cleaner is induced at too low of a RPM, or if you force the engine to stall by inducing too much cleaner at once, the engine may hydro-lock and bend a connecting rod(s).
In a well-ventilated area with the engine at operating temperature, slowly induce a bottle of upper engine and fuel injection cleaner into the engine with RPM off of idle enough to prevent the engine from stalling (typically around 2,000 RPM or so). Depending on the engine configuration, inject the cleaner through the throttle body or an engine vacuum hose/pipe. For best results, it is suggested to induce the cleaner through the throttle body with the special tool.
Turn the engine off after inducing the cleaner and allow the cleaner to soak with the engine off for two-and-a-half to three hours. Do not let cleaner soak for more than three hours as remaining deposits may start to harden back up again.
Add a bottle of GM Fuel System Treatment Plus to the fuel tank and fill the vehicle with one of the Top Tier gasolines listed at www.toptiergas.com and/or in-tank fuel system cleaner.
Test drive the vehicle extensively to circulate the fuel system cleaner.
Re-evaluate the concern to determine if it is repaired or improved at all. If the concern is improved but not repaired, it may be necessary to perform the above decarbonizing process a second time.
To complete the repairs, change the engine oil and filter, and advise the customer to only use one of the Top Tier gasolines.
Courtesy of Mitchell OnDemand.