Engine - Fuel Quality and Carbon Accumulations
86BMW03GROUP 06 Customer Relations
Bulletin Number 06 03 86 (1168) Page 1 of 2
Montvale, NJ March 1986 Technical Dept.
SUBJECT: Information Regarding Fuel Quality and Carbon Accumulations
The following information is made available for your use in discussing this matter with your BMW customers.
Over the past few months, all major car manufacturers have been receiving increasing complaints of rough starts, poor idling, stalling and poor acceleration. Because todays gasoline engines are designed for increased performance and fuel efficiency and, at the same time, reduced toxic components in the exhaust emissions, very sensitive high-technology components have to be used in the engines and in the case of BMW, computer controlled injection and ignition.
We have found along with the other car manufacturers that clogged fuel injectors and carbon deposits on the intake valves cause the above mentioned complaints. The source of the deposits is caused by the gasoline itself.
Gasoline consists of various hydrocarbons and various chemical structures within a boiling range of approximately 75~ to 410~F. When the engine is cold or in the first stages of warmup, the high boiling hydrocarbons do not burn completely causing the unburned particles to deposit on the injectors and the intake valves thereby creating carbon. The high olefin content of gasoline and the lack of sufficient quantities of appropriate detergents along with oxidation inhibitors contribute to this problem.
The problem of carbon deposits occurred in engines of older designs, but these engines had a very rich air-fuel mixture especially in the warm-up phase. Todays engines which provide maximum fuel efficiency, have very lean mixtures.
From a technical view point, carbon deposits on the fuel injectors produce an uneven spray pattern which then results in unequal fuel distribution in the combustion chamber, thereby causing rough and incomplete combustion.
To the driver of the automobile, the effect becomes rough starting, poor idling and basic poor driveability.
As carbon is porous, it is therefore capable of absorbing unburned fuel particles. This causes the already lean mixture to become even leaner and results in the above mentioned problems. At times, under certain engine conditions such as closed throttle, a portion of the absorbed particles can vaporize from the deposits and create an enrichment of the intake air causing the same effects.
At this time, the only solution is to remove the carbon build up from the intake valves. BMW as forerunner is addressing this condition and promoting the "Walnut Shell Blasting Technique". In addition, Techron manufactured by Chevron, was promoted through the BMW Dealer Network. Basically, the Walnut Shell Blasting Technique removes the carbon and the use of Techron reduces the effect of carbon and fuel deposits on the injectors. Presently, an injector cleaning process is under development and will be available shortly.
Most car manufacturers, including BMW, are in negotiation with all large gasoline companies in an effort to convince them of the necessity of increasing the content of cleaning additives and reducing the amount of olefin hydrocarbons and alcohol in their fuels. Presently, as can be seen from their advertising blitz, Mobil and Shell have been the first to react to this problem.
As additional information is available, you will be immediately informed.