Porsche Parts Catalog Porsche Accessories Catalog Porsche Technical Articles Porsche Tech Forums
 
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
Bookmark and Share

Pelican Technical Article:

Fuel Delivery Tests

Steve Vernon

Time:

1 hour1 hr

Tab:

$0

Talent:

**

Tools:

22mm, 19m wrench, fused jumper, measuring container, hose and adapters, fuel pressure gauge

Applicable Models:

Porsche 993 Carrera (1995-98)
Porsche 993 Carrera 4 (1995-98)
Porsche 993 Carrera 4S (1996-98)
Porsche 993 Carrera S (1998)
Porsche 993 Targa (1996-98)
Porsche 993 Turbo (1996-97)

Hot Tip:

Always use caution working with fuel

Performance Gain:

Proper fuel delivery and pressure

Complementary Modification:

Check all fuses

If you are having problems with your engine sputtering, lack of power or it is just not running right and you are going through the air, fuel spark tests here are a few tests that are critical to diagnosing fuel problems.

The fuel pressure is provided by the fuel pump which delivers high pressure fuel to the injection system. The pressure regulator maintains the pressure and sends the excessive fuel back to the fuel tank by the return line. The pressure regulator is responsible for the pressure maintenance and the system is not adjustable. There are two basic tests you can perform once you know that your fuel pump is running. To begin, check to see if the pump is functioning by turning the key while having an assistant listen for the pump; you should hear it running while actuating the starter. If your pump is not running please check your fuse and see our articles on DME relay trouble shooting. If the pump is running you want to check for both the delivery volume and the pressure in the system. This article will show you both tests.

Be prepared: Work in a well ventilated area. Keep a fire extinguisher near you at all times and know how to use it correctly. No sparks or open flame around and if you smoke now would be a really good time to quit: at least for the half hour it might take you to perform this job.

Just as with the fuel filter, injectors, or any other component of the fuel system, it's best to relieve the fuel system of any pressure before you go opening it up. You can do this by opening the fuel filler cap and/or removing the fuel pump fuse from the car's fuse panel and then starting the car and allowing it to idle until it runs out of fuel. Also, be sure to use some protective gloves and goggles whenever you're working with fuel.

Some fuel will spill out no matter what you do so be prepared to catch it with some rags and dispose of the rags in accordance with the regulations in your area. Never store fuel soaked rags anywhere; they are very dangerous.

Pull back the carpet in the front by the right side A-pillar and release the two clips on the fuse/relay panel cover (red arrows) and remove it from the vehicle.
Figure 1

Pull back the carpet in the front by the right side A-pillar and release the two clips on the fuse/relay panel cover (red arrows) and remove it from the vehicle.

Before you begin working on the fuel system you want to de-pressurize it.
Figure 2

Before you begin working on the fuel system you want to de-pressurize it. The best way to do this is to remove the fuel pump and oxygen sensor fuse from the fuse box in the front trunk and then start the engine and let it run out of fuel. Check your owner's manual to determine the right fuse. On our 1995 it was fuse number 26. The panel is set up so fuses 1-15 run along the side and fuses 16-41 run along the top. There is a fuse puller and spare fuses in the box (red arrow). Do not remove the DME relay yet (yellow arrow) as this will not allow the engine to run and you will not be burning the fuel in the system off. Remove the fuel pump fuse and run the motor until it stalls. Once the motor is out of fuel you can remove the relay (yellow arrow)

You will need to make a 15amp fused jumper to be able to run the fuel pump without turning on the ignition or running the motor.
Figure 3

You will need to make a 15amp fused jumper to be able to run the fuel pump without turning on the ignition or running the motor. I like to make mine with a switch as the delivery test needs to be timed and it is easier and more accurate to the control the pump with a switch.

For testing purposes use your 15 amp fused jumper wire and install the leads in terminals 30 (red arrow) and 87b (yellow arrow).
Figure 4

For testing purposes use your 15 amp fused jumper wire and install the leads in terminals 30 (red arrow) and 87b (yellow arrow).

Move to the engine compartment; if you started with the motor cold it should not have gotten very warn while burning off the fuel and by the time you get access to the fuel rail it should be cool; if it is not wait until the motor is cool before working on the fuel system.
Figure 5

Move to the engine compartment; if you started with the motor cold it should not have gotten very warn while burning off the fuel and by the time you get access to the fuel rail it should be cool; if it is not wait until the motor is cool before working on the fuel system. The fuel rail is below the blower motor (red arrow, cannot be seen).

Please see our articles on removing a Varioram and non-Varioram blower motor and assembly.
Figure 6

Please see our articles on removing a Varioram and non-Varioram blower motor and assembly.

To test the fuel delivery volume you will need to access the return line on the fuel regulator (red arrow).
Figure 7

To test the fuel delivery volume you will need to access the return line on the fuel regulator (red arrow).

Use a 22mm wrench to support the regulator housing (red arrow) and a 19mm wrench to break open and remove the fuel line fitting (yellow arrow).
Figure 8

Use a 22mm wrench to support the regulator housing (red arrow) and a 19mm wrench to break open and remove the fuel line fitting (yellow arrow). Even though you have run the system dry there will still be fuel that comes out of the line and regulator, be prepared with a rag to catch it and dispose of it in accordance with the regulations in your region.

Get a piece of hose a few feet long and place a 14mm X 1.
Figure 9

Get a piece of hose a few feet long and place a 14mm X 1.5 female fitting to one end. Thread the hose to the fuel pressure regulator and tighten. Place the end of the hose into a clean container that you can measure the amount in, make sure it is has at least 3 quarts capacity. The volume of fuel can cause the container to tip over so if you are working alone make sure you have it in a secure spot. Using your fused jumper run the fuel pump for exactly 30 seconds. If your battery is healthy you should have 0.85 liters or 0.9 quart after 30 seconds. Less fuel and you have a failing pump of a pinch in the line somewhere or a failing pump.

Next we are going to test the pressure in the system; you want to test both the system pressure cold and with the engine warm.
Figure 10

Next we are going to test the pressure in the system; you want to test both the system pressure cold and with the engine warm. Make sure you have reattached the return line to the regulator! There is Schrader valve or test port on the left side rail (red arrow) depending on what year 993 you have. You are going to be attaching your fuel pressure gauge to the port. Your gauge should cover between 0 and 6 bar.

The pump is capable of putting out high pressure and if the pump check valve gets stuck closed it can cause damage to the system; never let the fuel pressure get above 6 bar, shut down the test and check the check valve before moving forward.
Figure 11

The pump is capable of putting out high pressure and if the pump check valve gets stuck closed it can cause damage to the system; never let the fuel pressure get above 6 bar, shut down the test and check the check valve before moving forward. Attach the gauge and run the fuel pump using your fuse jumper. With the engine off and cool the system pressure should be 3.8 bar or 55psi. Remove the test jumper and start the motor, with the engine running and warm the pressure should be 3.3 bar or 48 psi. If your pressure readings are low slowly pinch the fuel return line and the pressure should rise; if the pressure doesn't rise your pump is probably going bad and if the pressure does rise then you probably have a failing pressure regulator. If the pressure is too high there may be kinks in the hose or return line to the tank.

Now remove the vacuum line from the pressure regulator and the pressure should rise to 4.
Figure 12

Now remove the vacuum line from the pressure regulator and the pressure should rise to 4.0-4.2bar or 58-61psi.

Bookmark and Share

  Search our site:    

View Cart & CheckOut | Project List | Order Status |  Help    

 

[Home] [Customer Service] [Shopping Cart] [Project/Wish List]
  [Privacy Statement]  [Contact Us] [About Us] [Shipping] [Careers]

Copyright © Pelican Parts Inc. -    DMCA Registered Agent Contact Page

Page last updated: Fri 12/9/2016 03:06:59 AM