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Fuel Pump Testing and Replacement
 
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Pelican Technical Article:

Fuel Pump Testing and Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$50

Talent:

***

Tools:

10mm socket, 19mm, 17mm, 8mm, 7mm wrenches, hose pinchers, Philips screwdriver

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)

Parts Required:

Fuel pump

Hot Tip:

Use all precautions when working around fuel

Performance Gain:

Better running engine

Complementary Modification:

Test your fuel pressures

Like any modern car the Porsche 993 needs consistent pressure and flow in its fuel system. The fuel pump has a check valve on the end of the output side that controls the direction of the flow. If the check valve fails, proper flow and pressure will not be maintained and the car will run rough or not at all. Please see our article on fuel system testing for some simple tests to determine if your check valve is going bad or has failed. The valve is a lot cheaper than replacing the entire pump and can be done with the pump partially in the vehicle.

The check valve is on the fuel pump and the fuel pump is located under the front right side of the vehicle near the tank. It has a protective plate over it that you can remove without removing any of the other under trays. When replacing, work in a well ventilated area, working outdoors is a good choice. Do not use incandescent work lights or power tools and DO NOT smoke: fuel and fuel vapors are highly combustible.

You will need to safely raise and support the vehicle, please see our article on safely raising and supporting your Porsche 993. Lift and support the vehicle as high as you can safely get it as you are going to want space to work under the car.

The fuel pump panel is held in place by a series of 10mm nuts and bolts (red arrows).
Figure 1

The fuel pump panel is held in place by a series of 10mm nuts and bolts (red arrows). It can be removed without removing any of the other panels.

With the hardware removed tilt the panel down and pull it back and out from the front panel.
Figure 2

With the hardware removed tilt the panel down and pull it back and out from the front panel.

You now have access to the fuel pump, lines and mount (red arrow) without removing any other panels.
Figure 3

You now have access to the fuel pump, lines and mount (red arrow) without removing any other panels. It is a tight fit in there so be glad you raised the car as high as you safely could.

The pump is covered in a rubber sound deadening protector and is mounted to the bracket with a large hose clamp.
Figure 4

The pump is covered in a rubber sound deadening protector and is mounted to the bracket with a large hose clamp. You will need to remove the three 10mm bolts holding the bracket in place and these bolts have rubber isolators and washers so take care when removing them and do not lose any parts.

Move the fuel lines and slip the pump up into the body of the opening until the wiring and banjo clear the body work and then lower that end first.
Figure 5

Move the fuel lines and slip the pump up into the body of the opening until the wiring and banjo clear the body work and then lower that end first.

With the unit out pinch off the fuel line from the tank to the input side of the pump (red arrow).
Figure 6

With the unit out pinch off the fuel line from the tank to the input side of the pump (red arrow).

Even though you have probably run the fuel system tests before you replace anything, make sure the pump is getting power.
Figure 7

Even though you have probably run the fuel system tests before you replace anything, make sure the pump is getting power. Remove the rubber protectors and place your voltmeter ends on the positive (yellow arrow) and the ground (red arrow). Bypass the fuel pump relay (please our article on preforming fuel tests for this information) and you should be getting 12 volts. If you are getting power and the connections are good then you have a faulty check valve.

Make sure to check the continuity of the ground wire separately.
Figure 8

Make sure to check the continuity of the ground wire separately.

While supporting the 17mm nut on the base of the filter use a 19mm wrench and loosen the capping nut holding the banjo bolt on (yellow arrow).
Figure 9

While supporting the 17mm nut on the base of the filter use a 19mm wrench and loosen the capping nut holding the banjo bolt on (yellow arrow). Be prepared to catch and dispose of the fuel that will escape out. Even though you have pinched the line off, the fuel in the pump will escape. There is very little room to work with the 17mm wrench and sometimes the fitting will loosen at the check valve. If that is the case go to the next step.

Next use a 7mm wrench and loosen the hose clamp on the supply line; again be prepared to catch the fuel that will escape.
Figure 10

Next use a 7mm wrench and loosen the hose clamp on the supply line; again be prepared to catch the fuel that will escape. Remove the hose and if your output connection loosened at the check valve you can now just spin the pump around the check valve until it is off, giving much more room to separate the banjo bolt.

If you got the banjo bolt off, you can change out the check valve while the unit is still attached to the vehicle if you like.
Figure 11

If you got the banjo bolt off, you can change out the check valve while the unit is still attached to the vehicle if you like. Use two 17mm wrenches and remove the check valve from the pump (red arrow).

When installing the new check valve make sure to replace both crush washers.
Figure 12

When installing the new check valve make sure to replace both crush washers. Installation is the reverse of removal.

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Page last updated: Wed 5/24/2017 03:18:24 AM