Some common fuel injection problems can be traced back to a faulty or non-operational fuel pump. If your pump is noisy and loud or the fuel pressure in the engine compartment is below what is needed for proper fuel injection operation, then it's probably time to replace it. The fuel pump is a not as simple a device as one might think. The fuel actually runs through the pump and acts as a coolant and lubricant for the entire assembly. Therefore, if you let your car run out of gas, make sure that you turn off the pump immediately or you might damage the internal components of the pump. Trust me--not much is worse than a broken or faulty pump leaving you stranded on the side of the road.
Typical fuel pump problems can sometimes be headed off in advance. If the pump is noisy and making loud clicking noises, then chances are that the bearings inside are worn and should be replaced. If the pump continues to make noise even after the ignition is shut off, internal check-valves in the pump may be showing signs of failure. The pump could seize up at some time, or the pressure to the fuel injection system could drop. Either way, the car will not be performing at its peak. Another symptom of failure is the pump getting stuck and then finally kicking in after turning the ignition on and off a couple of times. This could be a clear sign that you are living on borrowed time and that you should replace the pump immediately. Check the electrical connections to the pump before you replace it to make sure that it's not an electrical problem.
The first step in replacement is to prep the car. Remove as much gasoline out of the car as possible (see photos). Some other tips:
- Always have a fire extinguisher handy in case an emergency arises.
- Gasoline is highly flammable. When working around fuel and fuel line connections, don't disconnect any wires or electrical connections that may cause electrical sparks.
- Always remove the gas cap to relieve any pressure in the tank prior to working on the fuel system.
- Do not use a work lamp when working near fuel or fuel tanks. If you need some light, use a cool fluorescent lamp and keep it far away from the pump.
- Gasoline vapors are strong and harmful, and they can cause you to become drowsy and not think straight. Always perform work in a well-ventilated area with plenty of fresh air blowing through.
- Always disconnect the battery when working on the fuel system. Leave it disconnected for at least 30 minutes to allow any residual electrical charge in components to dissipate.
- Keep plenty of paper towels on hand, and wear rubber gloves to prevent spilling gasoline on your hands
- Be well grounded--don't do anything that will create static electricity. Keep all cell phones and pagers a safe distance away.
- Run the car so that the gas tank is near empty, and then remove the remaining fuel as detailed in Figure 1.
The first step is to remove the battery from the car (see Pelican Technical Article: Porsche 911 Carrera Battery Replacement Trickle Charger Installation). The lower battery tray acts as both a retaining platform for the battery and a cover for the fuel pump area. Underneath this tray, you will see the top of the fuel tank sending unit. Disconnect the connector that mates with the sender. Now, squeeze and disconnect the fuel lines and breather hose that feed into the top of the unit. There might be some small gas spillage here--have a roll of absorbent paper towels on hand. You might want to find an old pen to carefully plug the lines to prevent further leaks. If there is any fuel in your tank, now would be an excellent time to empty it. (See Figure 1 and Figure 2.)
The sender is held in place by the big circular disc with the risers on it. There is a special tool that is used to remove and tighten this black plastic ring. However, with a large flathead screwdriver or chisel and a small hammer, you can easily tap the plastic ring loose. Carefully remove the ring from the top of the sender.
Now comes the fun part. Make sure that you are prepared at this stage--in a heavily ventilated garage and with rubber gloves and plenty of paper towels. Pull up on the top of the sender, and the entire assembly should come right out of the tank (Figure 3). There is a big, thick O-ring that seals the pump to the tank--grab it and put it off to the side. See Figure 4 and Figure 5 for instructions on removal of the pump.
When reinstalling the pump into the car, make sure that the fuel hoses inside the tank don't interfere with the proper operation of the fuel tank sender. I found that my sender was getting stuck and the problem was the hoses. The solution was to open the tank up again and zip-tie the hoses out of the way. I would verify that they don't interfere with the movement of the sender before you button everything back up.
I recommend that you replace the large sealing ring with a new one. If you do opt to reuse the old one and it doesn't seal well, you might be plagued with a fuel smell in the car from that point on. Make sure that the big O-ring is properly sealed around the outside of the pump and will seal with the opening of the tank. Spin on the large circular ring and use the hammer/screwdriver tapping procedure to tighten it. I tightened mine about as tight as I could get it without feeling that I would break the ring.
Reconnect the fuel hoses and the electrical connector.
Reinstall and connect the battery after all fumes have subsided. Then crank the car over and see if it starts. If the car starts and runs for any length of time then the pump is working fine.
This photo shows a safe method for emptying the gas out of the tank in your Carrera. Disconnect the pressure side hose from the top of the pump and connect some clear plastic tubing to the barb (yellow arrow). Carefully connect the car's battery terminals up to a 12-volt supply, making sure that you wrap and insulate both terminals carefully. Jumper the relay in the driver's side footwell (see Figure 2) and turn on the ignition, and the pump should turn on and begin to pump fuel into your gas can. Watch the level carefully, and shut the pump off when the external tank fills up or when the Carreras fuel tank runs dry.
This photo shows the relay panel under the driver's side footwell. The fuel pump is not normally turned on unless the engine is running, but you can remove the relay and bypass it using a simple jumper wire as shown here. Remove the fuel pump relay (shown in the inset) and then jumper pins 30 and 87 (typically labeled 3 and 5 on the relay panel). This will cause the fuel pump to turn on automatically when you turn the key in the ignition.
Once you remove the battery and the lower tray/cover, you will see the top of the tank and the fuel sender. Squeeze the fuel line connectors and remove them along with the vent hose and the electrical connections (lower left). Use a large chisel and a medium-sized hammer to carefully tap on the outer ring that holds the fuel pump in place (upper left). It should turn and loosen up with a few taps. With the ring loose, pull out the fuel tank sending unit, and you should be able to carefully squeeze and remove the fuel supply hoses that attach to the bottom. When you reinstall the sending unit, be sure to line up the big arrow (blue arrow) with the three lines on the tank (green arrow).
The upper left inset shows the fuel pump sitting inside the empty fuel tank. I had a really difficult time removing the pump from the bottom of the tank. Supposedly you should be able to simply turn it with your hands and unlock it from the bottom, but my grip wasn't strong enough. Instead, I used a rubber oil-filter wrench to carefully wrap around the circumference of the pump. One solid twist of the tool, and the pump came free of its locking site on the bottom of the tank.
Installation is pretty straightforward. A: The red arrow shows the circular locking ring that the bottom of the fuel pump snaps into with a twist. This secures the pump to the bottom of the fuel tank. B: Shown here is the new pump installed. It looks slightly different than the original, but it's functionally equivalent. C: With the new pump in place, install the fuel tank sending unit into the top of the tank. Be sure to connect the hoses from the pump to the bottom of the unit. D: Shown here is the new pump installed with the new sending unit all buttoned up and ready for testing. Be sure to put some fuel back into the tank prior to starting the fuel pump up.