Fuel and Fuel System Related Problems



This Guideline enables dealers and their customers to benefit from cost reductions made possible through an established parts reusability and salvage program. Every effort has been made to provide the most current and relevant product information known to Caterpillar Inc. Since the Company makes ongoing changes and improvements to its products, this Guideline must be used with the latest technical information available from Caterpillar to ensure such changes and improvements are incorporated where applicable.

For questions or additional information concerning this Guideline, contact Caterpillar Dealer Support Division, Service Support (309) 675-5156.


Tooling and Equipment

General Information

Fuel Consumption Versus Ambient Temperature

Fuel mileage on heavy duty trucks with 3306 and 3406 Engines, can vary significantly depending on the ambient (outside air) temperature. On the average, the tank mileage (mpg) will decrease by several tenths of a mile per gallon in the winter and in some extreme cases a noticeable loss in power will also be observed. Only a small portion of these changes are related to the engine itself.

It has always been assumed that engines actually run better in cool or colder weather. This is true in most cases because of cooler inlet air and denser fuel. With these cold weather conditions, the engine will actually have a slightly increased flywheel horsepower. The problem lies in the increase in horsepower required to move the vehicle down the road in cold weather. Some of these factors are the denser air that the vehicle is moving through, rolling resistance of the tires and the increased friction in the drive train and wheel bearings. This change does not happen suddenly, but in a very predictable manner with temperature fluctuations.

Recently completed fuel consumption testing, compared several different truck configurations to a control truck over a period of time from late summer to mid winter. The different truck configurations were compared to the control truck which had no modifications made during the testing. The tests were all run on the same 180 mile (round trip) stretch of interstate. Each of the 90 mile (one way) legs of the trip were completed within ± 15 seconds unless traffic became a problem.

The ambient temperature on these runs varied from -2 to 32°C (28 to 90°F). Winds varied from calm to in excess of 25 mph from different directions. The tank mileage (mpg) was plotted against ambient temperature for each run made. A "best fit" line was drawn through the data shown in the graph. The overall temperature effect on tank mileage (mpg) was two percent reduction for every ten degree drop in temperature. At any given temperature, the tank mileage could vary ± 1/2mpg due to wind velocity and direction.

During the tests, it was observed that the tank mileage (mpg) would actually decrease at night as a result of the decrease in ambient temperature.

For example, the ambient temperature was 26°C (80°F) on one trip and -1°C (30°F) on another trip. On the 26°C (80°F) day the truck averaged 6.5 mpg and on the -1°C (30°F) day the truck averaged 5.85 mpg.

In addition, if a truck is put into service in the fall or winter, it has no warm weather history to show it's actual capability for several months. This can lead to customer dissatisfaction until the weather warms and the tank mileage (mpg) improves.

Illustration 1. Tank mileage comparison.

Why MPG Suffers in Cold Weather

During the colder, winter months truck owners with Caterpillar-Built Truck Engines often question a decrease in fuel efficiency. Reports have shown some owners do not understand the reasons for a decrease in miles per gallon (mpg). Reports have shown a decrease by as much as 1 mpg in some cases.

Many truckers use a mixture of Number 1 and Number 2 diesel fuel during cold weather. This mixture is used to prevent fuel waxing. The Number 1 diesel fuel is lighter; it has less wax than the Number 2 fuel. With a mixture of Number 1 and Number 2 diesel fuel, more fuel must be burned to get the same horsepower. Tests have shown that a 50-50 mix of Number 1 and Number 2 can give a reduction of 0.1 mpg.

It is also important to note that Number 1 diesel fuel costs more than Number 2.

Increased rolling resistance of cold tires is another factor that causes a decrease in fuel efficiency. It is estimated that a tire at -1°C (30°F) will give a reduction of 1 mpg in the first half hour of operation, when compared to operation at 21 to 29°C (70 to 85°F). In the second half hour of operation, the loss will be approximately 0.7 mpg. As tires warm up, the loss stabilizes at about 0.4 mpg.

A decrease in engine efficiency can result when the engine runs at a cooler temperature. Engine oil temperatures are lower, resulting in thicker oil and more drag (friction). This is especially true when the engine is equipped with outboard-mounted oil filters.

Rain, snow, or ice splashed against the engine, contribute to a cooler engine operation temperature. Traction is also decreased by precipitation. These factors combined can cause a further decrease of 0.2 to 0.3 mpg when the temperature is -1°C (30°F) instead of 21 to 29°C (70 to 85°F).

Additionally, transmission and axle lubricants stiffen, increasing drag. Cold ambient air is more dense, so the aero-dynamic drag increases. Winter winds are usually more severe and more frequent. A head wind or side wind will decrease fuel efficiency. Again, these conditions combined can reduce fuel efficiency by as much as 0.4 mpg.

Fuel efficiency is further reduced by a change in driving habits during the winter months. Idling time is increased. A driver will be more cautious on icy or wet roads. They will decelerate to a slower speed so additional acceleration is needed to return to cruising speed.

All these factors combined can cause a significant decrease in mpg during the winter months. To minimize the effects of the cold weather, you should make sure your water temperature regulators are working properly. On most engines, Caterpillar recommends replacement of the temperature regulator at 100,000 miles. See the Operation and Maintenance Guide for more specific information. If you have an on/off fan, make sure it is in good operating condition. Shutters can be installed to maintain a higher engine temperature. Also, keep idling time to a minimum. All these measures will help fight the effects of the cold weather. Although you may still see a decrease in mpg, it can be kept to a minimum.

Low Sulfur Fuel (USA Low Emission Engine Operation; Low Sulfur Fuel Outside the USA)

The emission regulations imposed by the US Federal Government require the sulfur in the fuel for on-highway diesel engines be reduced from the 0.5 percent level to 0.05 percent as defined in the ASTM D975 Fuel Specification. The ASTM D975-92 Specification now includes 5 grades of fuel:

Low sulfur No. 1-D

Low sulfur No. 2-D

No. 1-D

No. 2-D

No. 4-D

The sulfur fuel for on-highway trucks has been reduced to the new lower value of 0.05 percent. This low sulfur fuel has been available in the field for engine use since October 1, 1993 in the USA. At present, low sulfur fuel has been in Canada since the 1995-96 time frame. The 0.05 percent sulfur fuel has been in Europe since October 1996 and 0.05 percent sulfur fuel will be mandated in Japan in October 1997. There are no immediate plans for the rest of the world to initiate any lower sulfur fuel.

The energy content of the low sulfur fuel was not changed from the higher sulfur level fuel previously used. The data available from Caterpillar engines from the field and from lab testing did not indicate any wear difference with low sulfur fuel. Therefore, fuel consumption and engine operation with low sulfur fuel should not differ from operation with the normal sulfur fuels which have been used.

The USA higher sulfur fuel will have a coloring which will distinguish it from the low sulfur fuel. The USA No. 1-D, No. 2-D and No. 4-D fuels are required to contain a sufficient amount of blue dye (1,4-dialkyl amino anthraquinone) so its presence is apparent. Some of the fuels may contain an initial coloring which will change the blue dye to a bluish-green color.

The following information will help determine which Caterpillar engine crankcase oils should be used with this fuel.

* The present Caterpillar recommendation is API CF-4 performance oil.
* Any Caterpillar precombustion chamber (PC) and older direct injected (DI) engines that have been using API CD or CE oils should upgrade to API CF-4 oils with the low sulfur fuel. Limited engine test data indicates the API CD or CE oils should upgrade to API CD and CE oil formulations may produce more top ring groove and piston top land deposits than the API CF-4 oil formulations with low sulfur fuel.
* A new oil category is now under development which will be an upgrade in oil performance beyond API CF-4. This new oil will be a replacement for CF-4 when it becomes effective.

Fuel Nozzle Orifice Erosion

Nozzle orifice erosion is abrasive wear at the orifice inlets in the nozzle tip. It can result in increased fuel delivery and black smoke for 3406 Truck Engines equipped with 7000 Series fuel nozzles. A recent study of nozzle wear and fuel sample analysis shows abrasive contamination in fuel is the predominant contributor to nozzle orifice erosion.

This conclusion is based on a large sample of field return nozzles selected randomly from all geographic locations in the United States and Canada. Returned nozzles were tested for functional performance and analyzed for conformance to factory specifications. In this study, all nozzles met current production specifications for tip hardness, and no deficiencies in material and workmanship were identified in nozzle tips.

Nozzle flow rates varied over a wide flow range independent of service miles. Some nozzle sets flowed significantly above specification at low mileage, while other sets showed only slight flow increases after high mileage. Nozzles within sets experienced similar flow rates, supporting a system related cause for nozzle flow change independent of individual nozzle variability. Abrasive contamination in fuel was the only feasible explanation for nozzle set, flow rate variation.

If used crankcase oil is mixed with diesel fuel, published guidelines should be strictly followed. See Engine Data Sheet LEKQ3225. But, even if these guidelines are met, small debris (5 microns or less) in high concentrations can still produce premature fuel system wear.

Nozzle orifice erosion and other fuel system wear can increase exhaust smoke. Excess fuel delivery, reduced atomization, changes to nozzle spray pattern, and injection pump wear can all contribute to excessive black smoke.

While nozzles with eroded tips can affect visible smoke, the degree it affects fuel economy may be largely driver controllable. As fuel flow increases, the majority of this fuel increase is converted to power under maximum load conditions. If vehicle horsepower demand is minimized through reduced vehicle speed, aerodynamic drag, rolling resistance, etc., fuel mileage should not deteriorate even though the engine has additional reserve horsepower. In fact, additional reserve horsepower when used properly, can reduce shifting under certain conditions and potentially improve fuel economy.

Today's high performance fuel injection systems operate at higher injection pressures. Clean, high quality fuel, good fuel filters, and responsible maintenance practices are essential to long term fuel system reliability and performance.

Testing and Procedures

Fuel Dilution Troubleshooting Procedure

Reports indicate that some dealers may be using inaccurate test procedures when troubleshooting for fuel dilution of the lube oil on 3406B Engines. In some cases, the results of the tests performed may be misinterpreted. In other cases, the most likely causes are being overlooked. When troubleshooting for fuel dilution of the lube oil, use the procedures that follow in the sequence given.

1. Verify fuel dilution.

2. Test internal fuel lines.

3. Check fuel injection nozzles.

4. Test fuel transfer pump.

5. Test fuel injection pump housing.

Verify Fuel Dilution

Fuel dilution of the lube oil can be verified by two methods. First, by the test results of an S·O·S (Scheduled Oil Sampling). Second, by an increase in the oil level. If the second method is used, make sure the increase in the oil level is due to the addition of fuel.

Internal Fuel Lines

To test the internal fuel lines, it will be necessary to use the 5P-4150 Nozzle Testing Group and two lengths of wire braided hose capable of withstanding a pressure of at least 20,700 kPa (3000 psi).

NOTE: Use Special Instruction SEHS7292 for instructions on using the 5P-4150 Nozzle Testing Group.

Modify the two lengths of wire braided hose as follows:

1. Install a 6V-3989 Nipple on one end of each hose. This end will be connected to the nozzle tester with a 6V-4143 Coupler Assembly (Quick Disconnect).

2. Weld a section of fuel line and its nut to an appropriate fitting. Install this fitting on the end of one hose.

3. Weld an appropriate fitting to the bottom of a 2W-3409 Fuel Pump Bonnet. Install this fitting on the end of the second hose.

Check for internal leaks as follows:

1. Remove both valve covers and valve cover bases.

2. Wipe off all internal fuel lines, fuel injection nozzles, and/or nozzle adapters.

3. Disconnect one end of an external fuel line. Disconnect the end that is easier to work with.

4. Use the appropriate hose to connect the 5P-4150 Nozzle Testing Group to the external fuel line or to the fitting on the cylinder head fuel line adapter. This will make it possible to pressurize the internal fuel line and fuel injection nozzle.

5. Close the on-off valve, and open the isolation valve on the tester. Pump the handle rapidly until a pressure of 20,700 kPa (3000 psi) is obtained. Close the isolation valve.

6. Check for leaks at the areas shown in Illustrations 2 and 3.

Illustration 2. Location to check for internal fuel leaks with 1W-2950 or 7W-1902 Adapters.

Illustration 3. Locations to check for internal fuel leaks with 7W-1645 Adapter.

7. Repeat Steps 3 through 6 for all the cylinders.

Fuel Injection Nozzles

To check the fuel injection nozzles for leaks, remove the nozzles from the engine. Do not remove the bleed screws. Apply a pressure of 20,700 kPa (3000 psi) to the nozzle with the 5P-4150 Nozzle Testing Group. Check the nozzle for leaks in the areas shown in Illustration 3. Observe for 4 to 5 minutes. Small leaks are not readily apparent in the typical 1 to 2 minute check. It is recommended that all of the tests in SEHS7292 Special Instruction be performed at this time.

Illustration 4. Locations to check for fuel injection nozzle leaks.

Fuel Transfer Pump

This test must be performed with the fuel and the fuel transfer pump at a temperature between 18 and 29°C (65 and 85°F). Check the fuel transfer pump for excessive leakage as follows.

1. Fill the pump with fuel, and plug the outlet port.

2. Connect a regulated air supply and a shutoff valve to the inlet port of the pump. Set the regulator so the pressure is 520 ± 35 kPa (75 ± 5 psi). Do not open the shutoff valve at this time.

3. Mount the pump in a vise with the tappet about 3 to 5 degrees below horizontal, as shown in Illustration 5.

4. Wipe off the pump and turn the air supply ON. Make sure there are no leaks except from between the guide and tappet.

5. Wipe off the face of the guide again. Let a few drops of fuel fall off the guide before starting the count.

6. Count the number of drops of fuel that fall off the guide in one minute. The pump is good if six or less drops fall per minute.

Illustration 5. Location to check fuel transfer pump leakage.

Fuel Injection Pump Housing

This test must be performed with the fuel injection pump housing and the fuel at a temperature between 18 and 29°C (65 and 85°F). Test and inspect the fuel injection pump housing as follows.

1. Disconnect the fuel injection lines and the fuel return line from the pump. Cap all of the bonnets and return line fitting, so they will not leak when pressure is applied. Fuel injection lines can be modified for capping the bonnets.

2. Disconnect the fuel supply lines, and make sure the pump housing is full of fuel. Connect a pressure gauge and shutoff valve to the supply fitting, as shown in Illustration 6. Connect an air supply to the shutoff valve. Make sure the caps, connections, the shutoff valves, and the gauge do not leak.

3. Apply 480 kPa (70 psi) air pressure to the pump housing. Close the shutoff valve.

4. Observe the pressure loss over a period of five minutes. A pump is good if the pressure loss in five minutes is 35 kPa (5 psi) or less.

5. If the pressure loss exceeds 35 kPa (5 psi) in five minutes, remove each of the injection pumps one at a time. Inspect the seal surfaces of the barrel, timing spacer, and housing. Refer to Illustration 7. Check the surface finish of these parts. Make sure that none of these surfaces have any dirt, debris, nicks, cracks, or scratches on them.

6. Install all the injection pumps in the pump housings. Test the pump again for pressure loss.

Illustration 6. Test set up for fuel injection pump housing leak test.

Illustration 7. Locations to check for leakage.

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