Contrary to what many believe, deposits in both regions can start to form and build quickly, sometimes in under 1,000 miles, if the conditions are correct. Numerous cold starts and warm-up cycles, excessive idling, short trips and around-town motoring where the stop/start action is amplified are all ideal conditions for deposits to form quickly.
Deposits in the ports and on the backside of the intake valves are particularly detrimental since it will impact the engine's ability to breathe but also absorb fuel from the incoming charge. When this occurs the engine can experience excessively lean cylinders from the wetting of the carbon and induce abnormal combustion. CCD contribute to what engineers call ORI, or octane requirement increase, and will necessitate the engine to consume a fuel with a greater amount of anti-knock quality or have the tune severely compromised to compensate for the engine wanting to ping or knock.
The two components in the fuel identified as C9 and C10 hydrocarbons are held up as liquids by the deposits, the amount increasing with greater levels of valve deposits. During engine acceleration the air/fuel ratio becomes momentarily lean and could be excessive enough to cause a lean misfire or hesitation. The heavy fuel absorbed on the valves is then released during steady state operation and alters the desired air/fuel ratio by introducing additional fuel into the combustion chamber. This is known as the difference in the created and delivered air/fuel ratio and will seriously impact the engine's performance and driveability.
In simpler terms, IVD absorbs the additional fuel provided by the asynchronous fuel pulse and thus starves the engine. Then during steady state operation, as the charge passes over the IVD, the fuel-saturated carbon releases the hydrocarbons and richens the mixture.
IVD can build up to such an extent that it interferes with the closing of the valve, so burning can result. The type of deposit varies with the fuel and valve temperature. Sometimes it is soft and sticky and in other cases hard and brittle. Many researchers have found the heavy aromatic compounds from the reformulating process of modern gasoline are largely responsible for deposit formation. The presence of alcohol appears to increase the deposit rate on intake valves and such blends of fuel may require additional additive treatment to overcome the higher deposit levels.
The engine oil also plays a part in IVD. The valve stems are lubricated by oil flowing down onto the valve underside. Tests have proven that less expensive oils without the necessary additive package increase IVD. Some viscosity improvers are known to raise the level of deposits on the valves.
In regard to CCD, the most important effect of the residue is its impact on the octane requirement of the engine. In addition, the deposits can cause surface ignition, and if it is on the spark plug, engine misfire. The amount and nature of the CCD depends on the fuel, engine oil, engine design, driving style and state of tune.
Engine condition and its use also play a large part in deposit formation. It has been found that coolant temperature has the greatest effect and that air/fuel ratio is also important. Compression ratio and intake air temperature have such a small influence on CCD formation that they are considered non-offensive. The engine oil formulation contributes to combustion chamber deposits, and the amount depends on the oil consumption rate, particularly on the piston crown, and the volatility of the sulfated ash content of the lubricant.
 Dielectric compound was placed...  Dielectric compound was placed on the coil secondary terminals to ward off any corrosion and guarantee a strong spark. |  The throttle body was cleaned...  The throttle body was cleaned along with the IAC, and the minimum air rate and the TPS were set to Buick specifications. |  The MAF sensor was cleaned...  The MAF sensor was cleaned using CRC MAF Cleaner. It was important for all systems to be functioning properly for the best performance and accurate test data. |