Misdiagnosis: the biggest problem with fuel systems

The fuel pump and fuel system has evolved greatly since they were introduced in the early part of the last century.

In the old days, when few roads were paved and the automobile was a curious novelty, the gas tank was in the front of the car, on top of the engine, and the gasoline simply flowed through a tube into the engine by gravity. Not a complicated fuel delivery system, but it worked just fine. When mechanical fuel pumps were introduced, the pump would suck the fuel from the tank, and when the carburetor became a common item, the pump was driven by the camshaft and sent fuel through the system to the engine. When fuel injection came about in the 1980s, the fuel system and pump had to operate under higher and steadier pressures so fuel could get to the engine. Any drop in pressure would mean the engine would stop, as would the vehicle.

Fuel systems tougher, but prone to misdiagnosis

As the fuel pump and system evolved, the various mechanisms began to coalesce together where today the fuel pump and systems are all pretty much located in a simple all-in-one design that sits inside the gas tank. The designs are also tougher, made to last the entire useful life of the vehicle.

So why is it that fuel pumps and systems fail if they are so sturdy?

Jeff Richardson, product manager for fuel delivery products with Federal Mogul in Southfield, Mich., which handles the Carter Fuel Delivery Products line, said the biggest problem is not that the fuel pump fails, but it is often misdiagnosed. Often a technician will have a customer come in and complain that the engine does not seem to get any gas, or the pressure is too low for fuel to make the engine work. The immediate culprit would seem to be the fuel pump, so it is replaced.

However, Federal Mogul will often get a supposedly failed or faulty fuel pump only to find that the pump is in fine working order. So where is the problem?

Richardson suggested that before technicians blame the fuel pump, they should first look at whether the pump’s electrical system is actually working.

“One of the biggest problems we find is with the electrical system, making sure that the (fuel system) and pump has the proper voltage and the proper ground at the pump,” Richardson said. “It sounds like such a simple thing, making sure you have the proper battery voltage and there is low resistance on the ground circuit. But it is very common for people to find that they have a low psi, say about 30 psi on the fuel rail, and they quickly assume the problem must be with the pump.”

In reality, what often has happened is that the electric pump hanger assembly has developed a fault, causing a voltage drop to the pump. When this happens, it can mistakenly seem to a technician that the pump has failed.

Richardson said technicians should take the time to inspect the electrical connectors to see if soot or other material may have attached to the hanger cover and could be causing arching, or to see if there is a melted connector, or if the wiring insulation has become damaged. Any of these problems can cause problems for the fuel pump and system.

Warren Suter, director of product management, engine management products for the aftermarket division of Robert Bosch Corp. in Broadview, Ill. said whenever a customer comes in complaining of fuel pump problems, technicians should make sure “the pump is alive-and-kicking by doing a current test by back-probing the pump.”

“The second thing you have to test for is that the pump is delivering the right pressure, and you can usually do that measurement at a port on the fuel rail, because you have to make sure the engine is getting the right amount of fuel flow. We really feel that there is an educational need right now to let installers know the most appropriate way to diagnose a problem.”

Still, over long periods of use even the best fuel pumps and systems can fail.

“A fuel pump moves a large volume (of fuel) for such a small unit,” Antonio Ramos, assistant manager, aftermarket sales and service with Denso Manufacturing Canada Inc. in Mississauga, Ont. “There are many reasons why a fuel pump can break down that would not be much different from any other electrical component. Over time, the motor contacts wear and weaken the pump’s ability to maintain pressure in the system.”

Suter added fuel pumps, when tested, should never been tested ‘dry.’

“Electric in-tank fuel pumps are made to operate in a submerged state, sitting either in the fuel or filled with fuel,” he continued. “One of the biggest causes of fuel pump failure is to let the tank run empty. We try to council people on not letting the tank run to empty, and some automotive manufacturers recommend that you keep a third of a tank of fuel in the gas tank at all times. And it’s because of the problems that can be caused by having a fuel pump run dry that we recommend to technicians that they never test a pump dry.”

Dirty fuel means dirty pumps and systems

One of the main reasons why a pump and the fuel system can fail is contamination. In the days when cars had metal gas tanks, contamination was often a problem. The tanks would rust and that rust and other material would accumulate in the gas tank and foul the fuel, which in turn gummed up the pump, filters and other mechanisms.

With the introduction of plastic fuel tanks, this problem would seem to have been solved. Plastic does not rust and fuel tanks are designed to prevent material from falling into the tank when someone is pumping fuel at the gas station.

Bosch’s Suter agreed the designs of today’s gas tanks and fuel systems has reduced the possibilities of fuel contamination, but that still does not mean technicians should ignore the possibility. He added that when a fuel pump or other fuel system parts are replaced, a technician should flush the tank regardless.

“If foreign matter, such as dirt, gets into the fuel system, it can cause problems with the pump or injectors,” added Ramos. “Replacing the fuel filter regularly can extend the life of the pump.”

But right now, the greatest concern amongst some automotive manufactures is the introduction of ethanol-based fuels. Since, the 1980s, Canadian vehicles have been manufactured to run on ethanol-based fuels, up to the E10 standard.

According to Mike, Ricciuto, manager of vehicle, environmental and safety program for General Motors of Canada Ltd. in Oshawa, Ont. the tanks which store regular gasoline at service stations, any water and debris will fall to the bottom of the tank and not make their way into a vehicle’s gas tank when someone stops to purchase fuel.

“But ethanol is different,” Ricciuto added. “(Ethanol) absorbs water and the stuff at the bottom of the tank can get suspended in the fuel.”

This should not be a problem as the major retailers of gasoline in Canada have invested in new storage tanks and filter systems to eliminate the problems of debris and water. However, many smaller, independent gas retailers have not done so as the expense is quite great. Because these smaller retailers don’t have the right storage tanks or filters on the pumps, problems can develop with the ethanol fuel once it starts arriving, one problem being phase separation. This is when there is too much water getting into the storage tank and the ethanol falls out of the fuel. Because of the different densities of ethanol and gasoline, someone pulling up to the pump might one day get gasoline, while another day, they might be filling their gas tank with ethanol. While the car will still run, high ethanol will impact performance. And if the pumps are missing the proper filters, then any debris in the tank, which has become suspended in the fuel, will make its way into the car’s gas tank and into the fuel system.

REFERENCE LIST:

Denso Manufacturing Canada Inc.www.densocorp-na.com

Federal Mogul Corp. (Carter Fuel Delivery Products) www.federal-mogul.com

General Motors of Canada Ltd.www.gmcanada.com

Robert Bosch Corp.www.bosch.com