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Technical Forum: The engine cranks and has spark but won’t start. Does it need a new fuel pump?


8/24/2010

Counterman magazine presents 11 technical and sales topics in an easy-to-read question-and-answer format.
 
The engine cranks and has spark but won’t start. Does it need a new fuel pump?
A.  Maybe. A dead fuel pump will obviously prevent an engine from starting. But a number of other conditions can also cause a no start problem. These other possibilities should be investigated and ruled out before replacing the fuel pump.
Many fuel pumps are replaced unnecessarily. If a newly installed fuel pump fails to solve a starting or driveability problem, many customers blame the pump and bring it back. They may be swapping parts in an attempt to diagnose a problem, or they may think the pump is no good. Either way, it wastes time, money and goodwill. Returns also mean extra paperwork for the parts store, warehouse distributor and pump manufacturer, not to mention shipping costs and the potential of losing a repeat customer.

According to the Fuel Pump Manufacturer’s Council, nearly 10 percent of all the fuel pumps that are sold by auto parts stores are returned because the pump did not seem to work properly after it was installed. Yet 80 percent or more of the fuel pumps that are brought back for being “defective” work just fine when they are tested.

Some common causes of no starts due to no fuel include:

• A bad fuel pump relay. If the relay fails or has a bad electrical connection, it can’t energize the fuel pump and the engine won’t start. But it depends on the application. On many vehicles, the fuel pump power circuit is also wired through the oil pressure sender unit. When the engine is cranking and builds up oil pressure, power is routed directly to the fuel pump through this switch. So the engine should start even if the relay is bad.

• A blown fuse in the fuel pump circuit can prevent the pump from running. If a replacement fuse blows, there’s a short in the circuit that needs to be found and fixed.

• Corroded wiring connections and bad grounds at the fuel tank are also faults that can prevent a fuel pump from running or spinning fast enough to generate normal pressure.

• Low fuel pressure can also cause hard starting or a no start. Fuel injectors are designed to operate within a specific pressure range.

• Low fuel pressure can also be caused by a leaky fuel pressure regulator. The pump may be working fine, but if the regulator is leaking and can’t hold enough pressure in the fuel rail that supplies the injectors, the engine may be slow to start or may not start at all.

• Bad gas (too much alcohol or water in the tank) can also cause a no start that is not the pump’s fault.

• No gas in the tank. The fuel gauge may show fuel in the tank, but if the gauge is not reading accurately, the tank may in fact be empty. The fix here is to replace the sending unit or the gauge.

Q.  What else should be replaced when changing a fuel pump?
A.  Most electric fuel pumps are mounted inside the gas tank. Replacing the pump requires draining and dropping the tank. On top of the tank are rubber fuel hoses (inlet and outlet, except on returnless systems that only have an outlet hose), and evaporative emission control (EVAP) vapor hoses. All of these hoses should be closely inspected and replaced if hard, cracked, loose or leaking. The same goes for any other rubber hose connections in the fuel system.
A new fuel inlet filter sock inside the tank, and a new inline fuel filter are always recommended — especially if the old pump failed due to rust or dirt in the system. This may also require steam cleaning or replacing the old fuel tank with a new one.












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