Highway Speed Excessive Smoke and Fuel Knock - keywords 6.6 additive balance black contamination cylinder injector LBZ LLY lubrication misfire noise pump white

This PI was updated to clarify injector copper sealing leaks, and add information about early build injectors. Please discard PIP3491B.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

A customer may have a concern of excessive smoke and a fuel knock type noise while driving at highway speed. The customer concern discussed in this PI is more likely to occur in the 15,000 to 20,000 mile range, but may occur at a lower mileage. Excessive smoke may be described as white or black. The smoke associated with this concern will not be a small puff of smoke, but a large plume of smoke that does not dissipate quickly.

Complete current SI diagnostics for any symptoms or DTCs set. Get a large fuel sample from the fuel filter and check for contaminants. If there are signs of contaminants the fuel filter WIF (water in fuel) sensor must be removed. Hard particles will accumulate in the fuel filter WIF sensor area, and close visual inspection of this area will be needed. If contaminants are found, complete the SI procedure for Fuel System Cleaning. Evaluate the customer concern after the fuel system has been cleaned. If no contaminants are found, test drive the vehicle and try to duplicate the customer concern. If the customer concern cannot be duplicated, and the vehicle has only been at the dealer for one time, and one repair attempt, fill the fuel tank and add a fuel conditioner. Only alcohol free water demulsifiers should be used in General Motors diesel engines. The GM Diesel Fuel Conditioner®, The Racor Power Shot Plus®, and the Stanadyne® diesel fuel additives are alcohol free and utilize water demulsifiers to cope with water in the fuel (see service bulletin 03-06-04-017B). Other brands may be available in different areas; be sure that they clearly state that they are alcohol free demulsifiers before use.

If the concern of excessive smoke can be duplicated and the fuel knock is occurring, complete the current SI diagnostics for The Fuel Injector Balance Test with Tech 2.

Monitor and record all cylinder balance rates in drive and neutral.

Injectors that are above +/- 4.0 in park/neutral and +/-6.0 in drive will need to be replaced.

The injector must break both the +/-4.0 and +/-6.0 specification to qualify for replacement.

OR

Cancel the cylinders during the concern.

If canceling the cylinder with the Tech 2 stops the smoke or changes the fuel knock noise, that injector will need to be replaced.

If all the above diagnostics are inconclusive, or the concern is hard to duplicate, follow the steps below:

1. Remove the injector return lines and inspect the injector return line outlets for signs of rust or corrosion.
2. If rust or corrosion is found in the injector return line outlets remove the fuel pressure regulator from the fuel injection pump.
3. Inspect the fuel pressure regulator for corrosion.
4. If corrosion is found at the injector return outlets and at the pressure regulator, remove the fuel filter from the fuel filter housing and look inside the filter for sediment, rust, or signs of contaminates. Fuel filter inspection includes removing the WIF (water in fuel) sensor and inspecting the filter through the WIF sensor hole.
5. If rust is found in the injector outlets, the pressure regulator, and the fuel filter, all 8 fuel injectors will need to be replaced. Also replace the fuel filter and pressure regulator during the repair. The injectors will be requested and returned to the WPC and inspected for corrosion. This 8 injector repair is to gather information on fuel system corrosion. If this type of fuel system corrosion is found, the fuel tank must be removed and inspected for contaminants. If contaminants were found in the fuel tank keep a sample of what was found.
6. If no rust is found in any of the fuel system components and the vehicle is built before 8/20/04, refer to PI # PIP3400A for fuel injector copper sealing washer leaks. A copper seal that leaks (outside of combustion chamber) may be the sign of improper retaining bolt torque, or improper cylinder firing pressures. When a injector copper seal leak is found, there will be combustion soot found outside the combustion chamber (above the copper seal). If the copper seal leak is found the injector should be replaced. Soot found below the copper seal (inside combustion chamber) is not abnormal, and the injector should not be replaced. Be sure to clean injector bores following SI procedures.

Note: If a black smoke/fuel knock has been duplicated on a 2006 model year LLY or LBZ diesel engine, and there is no fuel system contamination/corrosion, check the vehicle build date. If vehicle has less that 4000 miles and was built prior to November 12, 2005 replace all 8 injectors. Complete any injector restriction processes.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.