Cleaning Excessive Carbon from Sticking Valves

2000-2015 GM passenger cars and light-duty trucks equipped with gasoline engines that experience engine misfire, rough idle, extended crank or crank/no start conditions may be the result of major carbon build-up on the intake and/or exhaust valves. One or more misfire DTCs may be stored in the Engine Control Module (ECM). Excessive carbon build-up on the intake and exhaust valves is often due to fuel contamination or incomplete burning of the fuel. (Figs. 14, 15)

 

f14-valves-1

Fig. 14

 

f15-valves-2

Fig. 15

When the engine is cold, the compression on multiple cylinders may be at 0 PSI. The engine also may pop through the intake or exhaust while cranking and the spark plugs may be fuel fouled. Some engines also may experience valve damage or cam followers that are out of position.

 

If these conditions are found, follow the misfire diagnostics in the appropriate Service Information. If valve damage is present or there are cam followers out of place, perform the engine mechanical repairs necessary to correct the condition. Also perform a valve cleaning to free up the sticking valves and to remove carbon from the valves and pistons.

 

Valve Cleaning

 

The valve cleaning procedure requires adding a bottle of GM Upper Engine and Fuel Injection Cleaner into the engine with RPM off idle enough to prevent the engine from stalling (typically around 2,000 RPM). It’s recommended to induce the cleaner through the throttle body with Kent-More Tool # J-45076 or J-35800-A or equivalent.

 

TIP: Extreme care must be taken not to hydro-lock the engine when inducing the cleaner, especially if it is induced without Kent-Moore Tool # J-45076 or J-35800-A or equivalent. If too much cleaner is induced at too low of a RPM, or if the engine stalls by inducing too much cleaner at once, the engine may hydro-lock and bend a connecting rod(s).

 

Tool # J-45076, originally released to Cadillac dealerships but now discontinued, includes the pressurized canister (Fig. 16, #1) and throttle body cleaning adapters. (Fig. 16, #2) The J-35800-A is another pressurized canister that can be used. If these tools are not available, use equivalent tools to perform the cleaning procedure.

 

f16-valve-tools

Fig. 16

 

After allowing the cleaner to soak with the engine off for 2.5 to 3 hours (do not let the cleaner soak for more than 3 hours as remaining deposits may start to harden up again), add a bottle of GM Fuel System Treatment Plus to the fuel tank and fill the vehicle with a Top Tier gasoline. Test drive the vehicle extensively to circulate the GM Fuel System Treatment Plus. Once repairs are complete, change the engine oil and filter.

 

For more information about Top Tier gasoline, go to www.toptiergas.com or refer to Bulletin #05-06-04-022.

 

A training video covering valve cleaning was included in the January 2013 Emerging Issues seminar (U.S.) and the March 2013 TAC Talk program (Canada). Refer to #PIP5029G for additional information and part numbers.

 

– Thanks to Tim Lightfoot

 

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