Auto Service World
Feature   December 1, 2008   by Tom Venetis, Editor

Don’t Always Blame The Fuel Pump

Experts Say Misdiagnosis, Fuel Contamination Are Still Common Problems

Pity the poor fuel pump. It is often the first part blamed when a problem happens in the car’s fuel system. But too often, when the ‘defective’ fuel pump is sent back to the manufacturer or examined by the shop more closely, it’s working just fine. So what is going on here? If the pump is in good working order, where is the problem in the car’s fuel system, and why do the surface tests say the pump is to blame?

Tom Fritsche, director of product management with Beck/Arnley in Smyrna, Tenn. says misdiagnosis in fuel system repairs is common and can be blamed on the pressures technicians face today. Needing to keep the bays full and moving cars in and out quickly in order to stay profitable, many technicians often focus on having the car’s electronics tell them what is wrong.

“The electronics in today’s vehicles are very sophisticated and it will point out to (the technician) that the fuel pressure regulator is bad, and the technician will change it, but they find they still have a problem with the fuel system,” Fritsche says.

What then happens is the technician puzzles over what might be the cause and the fuel pump is cited as the culprit: if the pressure is low, for example, it has to be the pump that is the problem.

Fritsche does not blame technicians for this. Instead, the pressures on them to work quickly, means technicians often do not go through the entire diagnostic process of elimination to find where the problem is actually occurring. The pump is blamed because on the surface, problems like low pressure, seem to logically point to the pump as the source.

Clayton Lindgren, gasoline fuel systems specialist for Robert Bosch in Broadview, Ill says fuel pumps do fail on occasion, through motor burn out or general fatigue of the moving parts. Certainly, the first step is to make sure the pump is working or if it has failed is to verify and measure fuel volume and pressure at the fuel rail.

“If insufficient, they need to find out why,” he adds. “Items to check include confirming the electrical signal at the pump, which should include thorough examination of the wiring and connectors, plus careful attention to the grounding, which is a surprisingly frequent cause of pump malfunction.”

In fact, many supposed pump failures in a fuel system are caused by problems with the electrical connections and harness. Dave Ehle, chief engineer, vehicle electronics with Delphi Products and Service Solutions in Troy, Mich. says one problem technicians should pay attention for is damage to the harness wires and insulation. If the insulation is damaged, water and road salt can work their way to the wires and corrode them causing a drop in voltage as the wires cannot provide the necessary power needed to operate the pump effectively.

“So the customer comes into the shop saying the car is sluggish, quit on him while on the road and on the surface it looks as if the fuel pump is not working correctly, that you have a worn pump,” Ehle says.

Another common mistake often made by technicians is not cleaning the tank out properly when replacing the pump.

Dan Williford, marketing manager with Airtex in Fairfiled, Ill, says in the rush to replace a fuel pump sometimes the fuel tank is not properly cleaned and flushed, leaving behind contaminates that caused the problems with the original pump. So putting in a new pump will only correct the problem for a short while before it succumbs to the contamination in the tank.

Contamination can also affect the regulator and injectors if it is particularly bad. Richard Dent, manager, vehicle electronics with Delphi says technicians must pay particular attention to the regulators as well, as a problem with the regulator could show up as a problem with the injectors.

If a technician gets what seems to be an injector problem, it is best to do a pressure check on the rail to make sure there is adequate pressure and seek out pressure drops that might indicate a leak somewhere. He also recommends that a fuel additive be used periodically to help clean the injectors as well as part of a maintenance routine.

Finally, all fuel systems experts say a problem that will likely be see more often is fuel systems being affected by ethanol-based fuel. In the United States, the introduction of E85 fuel has seen an uptick in older vehicles experiencing problems as the ethanol in the fuel mixture causes corrosion in the system.

“Ethanol, (E85) tends to be corrosive,” says Bosch’s Lindgren. “Galvanic action allows these fuels to conduct electricity and take an electrical charge, which draws ions out the metals and other materials they contact.”

This is why FlexFuel vehicles have their fuel system have their metal made from stainless steel so as to prevent this corrosion. Drivers of non-FlexFuel or older vehicles need to be reminded not to use this fuel. Even fuels with lower ethanol contents can over time also affect an older vehicle’s systems, but that seem pretty rare right now, but it is something to look out for.




Airtex Products



Delphi Corp.

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