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Steve, Auto Service Technician
Category: Car
Satisfied Customers: 5494
Experience:  25+ yrs experience as a professional working technician; ASE L1 master technician
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2002 Saturn: fuel pump..mechanic says..enough fuel pressure

Resolved Question:

What can cause fuel pressure to be low on my 2002 Saturn SL1 model. The mechanic said it was the fuel pump so I purchased a new fuel pump and that didnt' solve the problem. The mechanic says the new pump is not producing enough fuel pressure just like he said the old one wasn't; I have my doubts.
Submitted: 7 years ago.
Category: Car
Expert:  Steve replied 7 years ago.
   Diagnosing a fuel pressure problem should never involve guessing; at this point I really have no idea whether the mechanic you took the car to actually tested the system to identify the cause of the low pressure problem, or merely guessed at the cause.
   To understand what can go wrong, you need to understand how teh system works:
    The pump inside the tank sucks in fuel and pumps it out of the tank through a steel line.   This line connects to the pressure regulator (part of the fuel filter located just in front of the tank on the left side on your model).    Fuel passes through the filter, and out of the other end into the line that carries it up to the fuel rail on the engine.    Any excess fuel is bled off by the internal pressure regulator into a third line that returns it to the tank.
   When measuring fuel pressure, a pressure gauge is connected to the fuel rail on the engine.     If running pressure is below normal, there are really only 2 possible causes: either the fuel pump is not generating sufficient pressure, or the fuel pump is working fine but the fuel pressure regulator is malfunctioning and allowing the fuel to flow back into the tank instead of keeping the rail at a normal pressure.     You can determine which component is at fault by temporarily blocking the return line from the regulator to see if rail pressure rises to or above normal in response; if it does, then the pressure regulator is at fault.   If pressure does not rise to normal with the return blocked, then the fuel pump is not generating sufficient pressure.   If the fuel pump was purchased from a discount auto parts store, it would not be uncommon to get one that does not perfrom to specs. Discount parts stores buy their parts from the absolute cheapest overseas suppliers they can find, so they can compete with each other solely on price. As a result, the quality of parts store fuel pumps is often not very good.
   I would suggest having your mechanic measure the fuel pressure again, to verify that it is below specs.   if it is, make sure he tests the vehicle to positively identify the source of the pressure problem (pump or regulator) by blocking the return line while monitoring the pressure.   If the return line si rubber hose, he can pinch it shut with pliers; if it is steel or plastic line, an adapter tool with a shutoff valve may be required to perform this test (which he should have if he is in the repair business and diagnosing fuel system problems for people).
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