This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.
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 911 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. 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.
Before removing and replacing the fuel pump, try to get as much fuel out of the tank as possible. Be careful to turn the ignition off immediately if you let the car run dry, as this can burn out your fuel pump. Of course, if you are replacing it anyway, it doesn't really matter. Drive the car around until the fuel light goes on. The lower the fuel in the tank, the lower the pressure will be on the hose, and you will have a greater chance of blocking the fuel intake hose before you disconnect it. Make sure that you also perform the replacement procedure in a well-ventilated area that is free from any sources of ignition (gas/water heater, electrical cord, or lamp). If you need some more light, use a cool fluorescent lamp and keep it far away from the pump. Fuel will spill out when you replace the pump and you don't want it getting anywhere near the lamp. Disconnect the battery ground as well. Also make sure that you wear gloves, as gasoline and its components are known carcinogens that can easily be absorbed through the skin. Before you start working on the pump, disconnect the battery ground. You would hate to have the pump accidentally turn on when you are working on it. It's also a wise idea to have a fire extinguisher handy.
Another method of draining the tank is to attach a hose to the fuel line in the engine compartment. To do this, however, you need a special fitting that will attach to either the fuel pump or fuel accumulator. Attach the fitting to the bottom of the fuel pump or the bottom of the fuel accumulator and run the line into the gas tank of another car. Then turn the ignition on, and the fuel should be pumped directly into the other car's tank.
The belly pan located underneath the car covers and protects the fuel pump. Jack up the front of the car (see Pelican Technical Article: Jacking Up Your Car), remove this pan (see Project 59 for more details), and you should clearly see the pump. On some of the very early 911s, a mechanical pump similar to the one on the 356 and the 912 was used instead of the electric pump. This pump was located in the engine compartment and ran off of an attachment that connected it to the valve train. We won't cover this fuel pump in this project since not very many 911s used them.
Once you have access to the fuel pump, you'll need to clamp the lines. There are a few methods of doing this, but the easiest way seems to be by placing a pair of vise-grips on the line and clamping down. Tom Woodford of Factory Tour suggests that you cover the tips of the vise-grips as well with some duct tape so that the ridges of the tool don't damage the line. Also, make sure that you take a close look at the line itself to see if there is any damage or cracking in it. If there is, you should drain the tank fully, and replace the line. It's also a wise idea to clamp more than one vise-grips tool on the line to make sure that it is blocked as much as possible. Again, draining the tank to the lowest possible level will reduce the amount of fuel pressure in the line, and will make the vise-grips approach of clamping the line most effective.
Once you are confident that the lines are appropriately blocked, loosen and disconnect the hoses from each end of the pump. They should only be clamped on with small hose clamps. Again, inspect the fuel lines for cracks or other deterioration. Now, disconnect the electrical connections from the pump. Finally, loosen and remove the large clamp that holds the pump to the chassis. The pump should be easy to remove from the car at this point.
The installation of the new pump is straightforward, and basically the reverse of the installation procedure. Make sure that the rubber insulators completely cover the electrical connections to the pump. If they are cracked or worn, then they should be replaced. When you have finished replacing the pump, and reattached and clamped the hoses, slowly release the vise-grips and check the lines for leaks. Inspect the area where the vise-grips were clamped to make sure that no damage occurred to the lines.
Take the car out for a drive before you reinstall the belly pan. Fill the tank up with gas, and check again for leaks underneath the tank. When you are confident that the hoses are tight, then reinstall the belly pan, and you're done.
The fuel pump is located underneath the front belly pan. Access to the pump and its lines are obtained by removing this pan. Make sure that you work on the pump only in a well-ventilated area, and that you have as much of the fuel removed from the tank as possible. Keep all sources of ignition away from the pump while you are working on it.