Just thought i'd post this up for the people having fuel system problems. I've seen a few threads and i'm also having a few and found this. It's mostly general knowledge but it's good to have at hand.
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The electric fuel pump is the heart of every electronic fuel injection system. Let's review the basics of this critical fuel injection part.
Usually located inside or near the fuel tank, the fuel pump's job is twofold:
1) To push fuel from the tank to the injectors, and
2) To create sufficient pressure so the injectors will deliver the correct amount of fuel under all operating conditions.
The pressure developed by the pump, as well as the volume of fuel it flows, must both meet the vehicle manufacturers' requirements or engine performance, economy and emissions will suffer.
The amount of fuel pressure required for a given application will vary depending on the type of injection system (L-Jetronic, CIS, Motronic, etc.), the flow characteristics of the injectors and the engine's fuel requirements.
For example, certain Audi models with Bosch Motronic require 55 to 61 psi (3.8 to 4.2 BAR) of static pressure measured with the engine off. By comparison, a BMW may require 43 psi (3.0 BAR) on some models or 48 psi (3.3 BAR) on others. The differences may not seem like much, but a few pounds of fuel pressure can have a significant impact on engine performance and emissions.
Why Flow & Pressure Are So Important
A fuel pump that doesn't meet the OE minimum fuel flow or pressure requirements for your car can cause driveability and emissions problems.
A weak fuel pump or one that can't generate enough pressure can upset the calibration of your fuel system. This may cause the engine to run lean or starve for fuel under load, causing symptoms such as hard starting (hot or cold), poor idle quality, hesitation or stumbling when accelerating and a loss of high-speed power.
Low fuel pressure can also be a cause of lean misfire at idle and under load, which causes a dramatic increase in hydrocarbon (HC) emissions. A car experiencing this kind of problem usually won't pass an "enhanced" emissions test that measures exhaust emissions under simulated driving conditions on a dynamometer.
Low fuel pressure and/or lean misfire can also trigger the engine warning lamp on 1996 and newer cars equipped with OBD II (on-board diagnostics).
So, if the original fuel pump is weak or has failed, it's important to make sure your replacement fuel pump meets all OE fuel performance specifications. Bosch pumps do match OE requirements, but many brands don't - so beware when purchasing a new fuel pump for your car. Always remember - you get what you pay for. Is it really worth risking severe damage to your fuel injection system?
Why Fuel Pumps Fail
Electric fuel pumps run constantly, so after many years of service they can experience wear in the armature bushings, brushes and commutator. Pump vanes, rollers or gears can also wear causing a gradual loss of pressure and flow.
Accelerated wear may also occur if sediment or rust gets past the inlet filter sock. In some instances, a pump will fail because contaminants entered the pump and jammed it, causing the motor to overheat and burn out.
Your fuel pump relies on fuel passing through it for lubrication and cooling. Consequently, fuel starvation can be another factor that accelerates wear and may even cause pump damage under certain operating conditions.
Fuel Pump Diagnosis
If your fuel pump stops working (no noise, no line pressure), the first thing that should be checked is the pump's voltage supply and electrical connections. An open relay, blown fuse or loose wire may be all that's preventing the pump from working. Low battery voltage can also reduce the pump's ability to generate pressure by reducing the speed of the pump motor.
Measuring static output pressure and fuel delivery are the two standard diagnostic tests that can be used to determine a pump's ability to deliver fuel.
Static pressure is measured with a gauge attached to the fuel rail or teed into the fuel supply line with the engine off and pump energized. Fuel flow is measured by disconnecting the fuel supply line, energizing the pump for a specified number of seconds (engine off) and measuring the volume of fuel delivered into a container.
If static pressure or the volume of fuel delivered is less than your car manufacturer's specifications, your fuel pump needs to be replaced. Replacement would also be required if the pump's check valve has failed (inability to hold residual pressure in the system after the ignition is turned off).
Replacement Fuel Pump Precautions
Selecting the "right" replacement fuel pump involves more than looking up the year, make, model and engine size of your car. It also means choosing a pump that meets all OE performance specifications and fits the same as your original - Bosch pumps do, but many other brands don't. Bosch is, of course, the company that pioneered fuel injection technology.
To maximize coverage with the fewest number of part numbers, some major aftermarket companies have taken consolidation to the extreme. They have over-consolidated their fuel pump applications by using only a few fuel pumps for a wide range of car applications.
Because of the many different performance requirements and pump designs used in today's cars, this often causes performance and fit problems. For example, when fuel pumps from three of Bosch's competitors were compared against the OE specifications for the cars the pumps supposedly fit, some glaring shortcomings were discovered:
Example #1: One pump from Competitor A covers 70 OEM part numbers, yet has a fuel delivery rate 42 to 50 percent less than the OE specifications.
Example #2: A pump from Competitor B also covers 70 OEM part numbers, but has a fuel delivery rate 25 percent less than OE specifications.
Example #3: One pump from Competitor C covers a whopping 153 OEM part numbers but has a fuel delivery rate 30 to 42 percent less than many OE specifications and exceeds OE electric consumption by 33 to 50 percent!
Example #4: Some Bosch competitors were found to be using fuel pumps that are a different size or type than the original. Competitor B uses a 38mm diameter pump for 51mm diameter pump applications. To make it fit, they include a rubber sleeve. To make matters worse, the pump's outlet pipe location is off-center, which causes the pump to jut out half an inch more than the OE fuel pump. The same company also substitutes an inner-gear style pump for cars that were originally equipped with a turbine pump, which can cause unwanted pressure fluctuations and noise.
Example #5: Another trick some competitors employ is to use the same inlet filter screen on a wide variety of cars. Companies A, B and C all use only one filter screen for more than 20 different OEM applications. This results in a poor fit on some cars because of variations in the shape of the fuel pot reservoir inside the tank.
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The electric fuel pump is the heart of every electronic fuel injection system. Let's review the basics of this critical fuel injection part.
Usually located inside or near the fuel tank, the fuel pump's job is twofold:
1) To push fuel from the tank to the injectors, and
2) To create sufficient pressure so the injectors will deliver the correct amount of fuel under all operating conditions.
The pressure developed by the pump, as well as the volume of fuel it flows, must both meet the vehicle manufacturers' requirements or engine performance, economy and emissions will suffer.
The amount of fuel pressure required for a given application will vary depending on the type of injection system (L-Jetronic, CIS, Motronic, etc.), the flow characteristics of the injectors and the engine's fuel requirements.
For example, certain Audi models with Bosch Motronic require 55 to 61 psi (3.8 to 4.2 BAR) of static pressure measured with the engine off. By comparison, a BMW may require 43 psi (3.0 BAR) on some models or 48 psi (3.3 BAR) on others. The differences may not seem like much, but a few pounds of fuel pressure can have a significant impact on engine performance and emissions.
Why Flow & Pressure Are So Important
A fuel pump that doesn't meet the OE minimum fuel flow or pressure requirements for your car can cause driveability and emissions problems.
A weak fuel pump or one that can't generate enough pressure can upset the calibration of your fuel system. This may cause the engine to run lean or starve for fuel under load, causing symptoms such as hard starting (hot or cold), poor idle quality, hesitation or stumbling when accelerating and a loss of high-speed power.
Low fuel pressure can also be a cause of lean misfire at idle and under load, which causes a dramatic increase in hydrocarbon (HC) emissions. A car experiencing this kind of problem usually won't pass an "enhanced" emissions test that measures exhaust emissions under simulated driving conditions on a dynamometer.
Low fuel pressure and/or lean misfire can also trigger the engine warning lamp on 1996 and newer cars equipped with OBD II (on-board diagnostics).
So, if the original fuel pump is weak or has failed, it's important to make sure your replacement fuel pump meets all OE fuel performance specifications. Bosch pumps do match OE requirements, but many brands don't - so beware when purchasing a new fuel pump for your car. Always remember - you get what you pay for. Is it really worth risking severe damage to your fuel injection system?
Why Fuel Pumps Fail
Electric fuel pumps run constantly, so after many years of service they can experience wear in the armature bushings, brushes and commutator. Pump vanes, rollers or gears can also wear causing a gradual loss of pressure and flow.
Accelerated wear may also occur if sediment or rust gets past the inlet filter sock. In some instances, a pump will fail because contaminants entered the pump and jammed it, causing the motor to overheat and burn out.
Your fuel pump relies on fuel passing through it for lubrication and cooling. Consequently, fuel starvation can be another factor that accelerates wear and may even cause pump damage under certain operating conditions.
Fuel Pump Diagnosis
If your fuel pump stops working (no noise, no line pressure), the first thing that should be checked is the pump's voltage supply and electrical connections. An open relay, blown fuse or loose wire may be all that's preventing the pump from working. Low battery voltage can also reduce the pump's ability to generate pressure by reducing the speed of the pump motor.
Measuring static output pressure and fuel delivery are the two standard diagnostic tests that can be used to determine a pump's ability to deliver fuel.
Static pressure is measured with a gauge attached to the fuel rail or teed into the fuel supply line with the engine off and pump energized. Fuel flow is measured by disconnecting the fuel supply line, energizing the pump for a specified number of seconds (engine off) and measuring the volume of fuel delivered into a container.
If static pressure or the volume of fuel delivered is less than your car manufacturer's specifications, your fuel pump needs to be replaced. Replacement would also be required if the pump's check valve has failed (inability to hold residual pressure in the system after the ignition is turned off).
Replacement Fuel Pump Precautions
Selecting the "right" replacement fuel pump involves more than looking up the year, make, model and engine size of your car. It also means choosing a pump that meets all OE performance specifications and fits the same as your original - Bosch pumps do, but many other brands don't. Bosch is, of course, the company that pioneered fuel injection technology.
To maximize coverage with the fewest number of part numbers, some major aftermarket companies have taken consolidation to the extreme. They have over-consolidated their fuel pump applications by using only a few fuel pumps for a wide range of car applications.
Because of the many different performance requirements and pump designs used in today's cars, this often causes performance and fit problems. For example, when fuel pumps from three of Bosch's competitors were compared against the OE specifications for the cars the pumps supposedly fit, some glaring shortcomings were discovered:
Example #1: One pump from Competitor A covers 70 OEM part numbers, yet has a fuel delivery rate 42 to 50 percent less than the OE specifications.
Example #2: A pump from Competitor B also covers 70 OEM part numbers, but has a fuel delivery rate 25 percent less than OE specifications.
Example #3: One pump from Competitor C covers a whopping 153 OEM part numbers but has a fuel delivery rate 30 to 42 percent less than many OE specifications and exceeds OE electric consumption by 33 to 50 percent!
Example #4: Some Bosch competitors were found to be using fuel pumps that are a different size or type than the original. Competitor B uses a 38mm diameter pump for 51mm diameter pump applications. To make it fit, they include a rubber sleeve. To make matters worse, the pump's outlet pipe location is off-center, which causes the pump to jut out half an inch more than the OE fuel pump. The same company also substitutes an inner-gear style pump for cars that were originally equipped with a turbine pump, which can cause unwanted pressure fluctuations and noise.
Example #5: Another trick some competitors employ is to use the same inlet filter screen on a wide variety of cars. Companies A, B and C all use only one filter screen for more than 20 different OEM applications. This results in a poor fit on some cars because of variations in the shape of the fuel pot reservoir inside the tank.
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