EXPERTEC Technical Service Bulletins (11-90-035)

EXPERTEC TECHNICAL SERVICE BULLETINS

TECHNICAL SERVICE BULLETIN

CARBON DEPOSIT FORMATION ON PORT FUEL INJECTORS

Model(s): Oldsmobile Models with Port Fuel Injectors

Bulletin No.: 11-90-035

Section No.: 6C

Date: November 30, 1990

SERVICE INFORMATION

A deposit-fouled fuel injector can cause an uneven spray pattern (see Fig 1 ) possibly causing severe driveability symptoms. Fouled injectors may result in uneven idle, reduced power, poor fuel economy, hard starting, increased emissions and even stalling (particularly if the ECM can no longer correct for insufficient fuel flow).

Some companies who market fuel injection cleaning systems claim that their cleaner has benefits to clean dirty fuel injectors. They also recommend that the injectors be cleaned before diagnosing driveability problems frequently associated with clogged injectors (such as hard starting, hesitation, stirging, stalling or even poor gas mileage). These companies also suggest cleaning the injectors as part of routine engine maintenance and prior to emissions service testing or following a failed emissions test. The Bosch pintle-type of injector used in the 3.0L and 3.8L engines are the only injectors used on Oldsmobile vehicles that would benefit from a fuel injection system cleaning. The Quad- 4, 2.8L, 3.1L, 3300, and 3800 engine uses fuel injectors manufactured by both MULTEC and BOSCH with a "director plate" in the bottom of the injector. These injectors use a spacer plate with orifices for fuel flow that resists the formation of deposits. Oldsmobile feels that the use of injection system cleaners on vehicles with director plate designed injectors is not justified because of the cleaner fuels sold today and the injectors tendency to resist deposit formation.

Deposits can form on Bosch pintle-type fuel injectors during the "hot soak" period immediately after the engine is turned off. Short-trip driving also increases the chances of deposits forming on systems using the pintle-type of fuel injector (see Fig 2 ). Fuel injection systems using a spacer plate at the bottom of the injectors resists the formation of deposits due to the design of the spacer plate (see Fig 3 ).

A fuel injector sprays fuel (in the quantity calculated by the ECM/PCM) into the intake port just upstream of the valve. When the intake valve opens, the air that is induced takes the fuel spray with it. During engine operation, fuel flows through the injector metering orifice. After the engine is turned-off, the remaining fuel on the pintle-type of injector evaporates and may cause deposits to form due to the high temperature environment.

Deposit formation can also be increased by "fuel weepage" after the engine is turned off. "Fuel weepage" is the passing of fuel beyond the injector seat during hot soak. Since the fuel in the system is still under pressure after the engine is turned off, the residual pressure may cause fuel to "weep" past the seat of the metering orifice onto the pintle (the opening in the metering orifice is approximately 0.002", or about the width of a human hair). This results in more fuel on the pintle during the period immediately after the engine is turned off and may cause deposits, depending on the rate of weepage. The result of deposit formation on a pintle-type of injector is shown in Fig 2 .

It should be noted that deposits do not form at the same rate in all engines or all injectors in the same engine. Some tests have indicated that higher temperatures may lead to increased deposits.

Regardless of the cause or causes of injector deposits, preventative measures have been taken by the petroleum industry to reduce injection deposits. In 1985, General Motors asked the petroleum industry to increase the level of detergents in their gasolines to address this problem. The petroleum industry responded by increasing the level of detergents/deposits control additives to levels that were sufficient to keep port fuel injectors clean, and in some cases, at levels that provide injector cleaning.