Repairs :: Testing A Fuel Pump
Fuel pumps have a check valve that prevents the fuel from draining back into the tank when the engine is shut off. You'll need a fuel pressure gauge and the adapters to fit your vehicle. If your diagnostics lead you to believe you have a fuel pump problem, here's the proper way to check out the pump. If yours passes that test, move on to the electrical tests.. It's a major job to replace it and these pumps are expensive. if you are handy you can probably replace the battery and or alternator in your car. The problem is that the problem with your vehicle might not be caused by the battery. finding electric problems in a car can be challenging. It is very difficult to trace one of the hundreds of wires in a vehicle. You need a specialized electric automotive repair shop to find most electric problems in a vehicleor the alternator! It might be a short in a wire, a bad ground or just a sticky relay that causes the battery to drain or the alternator to not charge the battery. That is why there are professional auto repair shops! A cool engine provides two things: better working conditions with less chance of a fuel-spill related fire, and a more accurate reading of residual fuel pressure after sitting for a long time. Check out a printed or online shop manual for those.
Perform the fuel pressure check first thing in the morning, with the engine cool. Usually, the tech looks for pressure to stay within 5 lbs of the running pressure.
Fuel pumps in fuel injected vehicles are mounted inside the gas tank. So before you replace one, you better do your homework. A scope will tell you if you have a bad winding in the pump since it detects every lobe on the armature.
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If your fuel pressure and leakdown readings are within spec, you'll need to check fuel delivery volume. Just like any other electric motor that meets resistance, it uses more power. Yup, that's an important test especially if your performance problems occur at high speeds or heavy throttle. If the valve isn't working properly, you'll have fuel drain back and that causes hard starting first thing in the morning. Some auto parts stores rent this test gear. Remember, the pump is always pumping against resistance (the pressure regulator and he fuel injectors). So like an EKG at your doctor's office, measuring current draw at different throttle openings tells you how the pump is performing. If you can't find a spec, use this rule of thumb-a fuel pump should deliver 1 quart of fuel in 30 seconds. You'll also need the specs for your vehicle. A properly operating auto repair fuel pump should draw from 3 to 6.5 amps.
If you own a scope, you can get even better readings. I've seen too many DIY mechanics make the assumption that their engine running problems are due to a bad pump. First, perform a fuel pressure test. Several hundred dollars later, they still have the same problem.
The electrical test can spot a fuel pump problem that evades all other diagnostics. Shop manuals have a specific procedure for performing this "leakdown" test if the vehicle is brought in warm with high fuel pressure. Some manufacturers list a volume of fuel for a specified period of time
Perform the fuel pressure check first thing in the morning, with the engine cool. Usually, the tech looks for pressure to stay within 5 lbs of the running pressure.
Fuel pumps in fuel injected vehicles are mounted inside the gas tank. So before you replace one, you better do your homework. A scope will tell you if you have a bad winding in the pump since it detects every lobe on the armature.
http://www.articlebiz.com/article/439885-1-testing-a-fuel-pump/
If your fuel pressure and leakdown readings are within spec, you'll need to check fuel delivery volume. Just like any other electric motor that meets resistance, it uses more power. Yup, that's an important test especially if your performance problems occur at high speeds or heavy throttle. If the valve isn't working properly, you'll have fuel drain back and that causes hard starting first thing in the morning. Some auto parts stores rent this test gear. Remember, the pump is always pumping against resistance (the pressure regulator and he fuel injectors). So like an EKG at your doctor's office, measuring current draw at different throttle openings tells you how the pump is performing. If you can't find a spec, use this rule of thumb-a fuel pump should deliver 1 quart of fuel in 30 seconds. You'll also need the specs for your vehicle. A properly operating auto repair fuel pump should draw from 3 to 6.5 amps.
If you own a scope, you can get even better readings. I've seen too many DIY mechanics make the assumption that their engine running problems are due to a bad pump. First, perform a fuel pressure test. Several hundred dollars later, they still have the same problem.
The electrical test can spot a fuel pump problem that evades all other diagnostics. Shop manuals have a specific procedure for performing this "leakdown" test if the vehicle is brought in warm with high fuel pressure. Some manufacturers list a volume of fuel for a specified period of time
