This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
In this project, I'll walk you through the process of replacing your fuel injectors. Now, before we begin, a good question to ask would be why would you want to replace them to begin with? There are several myths and misunderstandings regarding fuel injectors. The first one is "bigger injectors will give you more power." This statement is completely false. It's the equivalent of saying that adding more lights to your already brightly -lit living room will make you see better.
The fuel injectors that are in your Boxster are more than adequate for stock engines, and supply more than enough fuel for maximum power and open throttle. For your engine to achieve maximum power, it must have an air/fuel ratio maintained within a certain range. Adding more fuel to the mixture makes it richer, and won't necessarily give you any more power. In fact, it is typically the opposite - a richer mixture will foul plugs and won't ignite as easily. The goal of any good fuel injection system (whether it be carburetors or electronic fuel injection) is to maintain the air/fuel ratio (typically about 14.67:1) for ideal combustion and power. Adding higher flow or larger injectors disrupts the balance of the engine, makes the engine's fuel management system run richer, and generally decreases power from ideal levels. It's the same principle as adding more high powered lights to your living room - if the room was adequately lit to begin with, then you won't see better - you'll see worse, because it will be too bright for your eyes.
So what are the exceptions to this rule? There are a few. Major changes in the displacement or flow of the engine can cause the engine to run lean. Examples would include if you increased the displacement of your engine, changed your camshafts, or if you added a turbo or supercharger. The supercharger compresses the air/fuel mixture and allows more of it to exist within the same size combustion chamber. Therefore, ideally there should be more fuel injected into the combustion chamber when compressed with a supercharger, then is normally injected on a normally aspirated engine. For owners who add a supercharger or turbo to their car, they need to be especially concerned about keeping the engine's mixture correct - the tendency is for these cars to run too lean, which can lead to destructive problems like detonation or overheating (see Pelican Technical Article: Superchargers / Turbo Chargers).
In general, you should not upgrade or replace your injectors with larger ones, unless you have made a significant engine modification that would cause the engine to run lean. If you are replacing injectors, then make sure that you use ones that have stock flow rates for your engine - don't buy ones that have higher flow rates thinking that it will give you more power - it won't.
So why would you want to replace your injectors then? Well, as the engines get old, the injectors tend to fail and leak. If you pull fault codes out of your computer, it may tell you that you have a faulty or leaking fuel injector. See Project 20 for more details on how to do this. You may also find that you can see or smell a particular injector leaking. If this is the case, you may not have to replace the injector itself, but may only need to replace the injector o-rings.
The first step is to prep the car. I like to tell people to pull out the fuse for the fuel pump (see Pelican Technical Article: Fuel Filter Replacement), and then try to start the car. The car will turn over and then die. Do this about 2-3 times - it will help drain excess fuel out of your system. Then, make sure that the car has cooled down - you don't want to be working with gasoline when the car is hot. Have a fire extinguisher handy - there will be some spillage of fuel - it's nearly impossible to prevent. Also, wear chemical resistant gloves if you don't want to get any gasoline on your hands, and make sure that you have plenty of paper towels or rags on hand to help you clean up. Perform the injector removal in a clear, open, and well-ventilated space, and it may not hurt to have an assistant around in case there are any problems.
Begin by removing the top engine cover (see Pelican Technical Article: Air Filter / Pollen Filter Replacement) and disconnect the battery (Pelican Technical Article: Battery Disconnect Switch / Battery Buddy Installation). On the 2005 and later cars, if you wish to remove the injectors on the left side of the car, then you'll probably want to remove the air cleaner to give yourself more working room (Pelican Technical Article: Cold Air Intake Installation).
Now, loosen the clamp that holds the fuel line to the top center of the motor. Remove the connectors from each of the fuel injectors (see Figure 1). With the clips disconnected, you should be able to remove the wire harness from the tops of the fuel rail, and move it out of the way. Now you should have much better access to the injectors - it's time to remove them from the fuel rail. The fuel rail is the long, round metal bar that runs along the top of the injectors, and is held onto the manifold with a few bolts (see Figure 1). Depending upon the configuration in your car, and which side you are working on, you may have to disconnect the main fuel lines to the rails in order to give yourself more working room. It may also be useful to remove the front panel to assist in the disconnection of these lines.
At this point you should be able to pull off the fuel rail from the top of the injectors. Use caution and work from the front of the car to the rear - pulling and making progress slowly. The injectors have big fat o-rings that are pressed into bores in the fuel rail - you are battling these o-rings as you lift up on it, and pull it out.
When you have lifted up your fuel rail (expect some fuel spillage from the rail), you should be able to push it out of the way enough to be able to pull out the injectors. With the injectors no longer attached to the fuel rail, you can now pull them out of the manifold. They are held in place using the same type of big fat o-ring at the tip of the injector. Simply pull straight up on the injector and it should come out of the manifold. You may have to tug a little bit to get it out, but don't use excessive force. Sometimes repeated wiggling helps. Be careful of the injector tips - they are made of plastic, and are not available separately from the $150 injectors. Do not damage them.
With the injectors out of the manifold you can now take them to be cleaned and calibrated. Over the years, the injectors become dirty and may also not distribute flow evenly amongst all six. It costs about $150 for all six to be cleaned, tested, and calibrated. New injectors cost anywhere from $150-$200 apiece, making their replacement a somewhat pricey endeavor.
There are three types of injector leaks: they can leak fuel into the manifold from the nozzle, they can leak fuel into the engine compartment from the fuel rail, and they can leak air (vacuum leak) from the manifold. The first leak cannot be fixed at home - you need to have the injector repaired or replaced (I recommend replacement, as it will be probably be pretty old anyways). The fuel rail leak is easy to contend with - simply replace the old, fat o-ring that seals the injector to the fuel rail (PN: 944-110-901-01). This should be done anytime the injectors are out of the car.
The third leakage area is a bit of a catch-22. On some of the early cars (through 2000), the tip of the injector needs to be removed from the injector. While this seems easy, and indeed it is easy to remove, it is just as easy to damage the tip when you remove it. The method that I used to replace one of the seals in the tip works well, but it also did slightly ding and damage the green plastic, fragile tip of the injector (see Figure 3). The 2001 and later injector o-rings can be easily removed without damaging the injector.
If you are replacing all your injectors or the o-rings, make sure that you place a very tiny, tiny bit of white lithium grease, or the Porsche recommended Optimol MP3 on the edges that will be pressed into the fuel rail and the manifold. This will aid in the insertion of the injector and the reassembly of the fuel rail. It will also help to prevent the o-ring from pinching, and will guard against tiny leaks as well.
Installation is basically the reverse of removal. You may find it easier to insert the injectors into the manifold first if you have enough room (instead of into the fuel rail first). Double-check to make sure that all of the fat o-rings are securely seated when you reattach the fuel rail. When you are ready to fire up the car, have an assistant on hand, in case there is a fuel leak. Have them watch the injectors and the fuel lines to make sure that there are no leaks.
Unplug the wire harness from each injector (yellow arrow). Unclip the harness from the fuel rail (blue arrows), and place it off to the side. Then unbolt the fuel rail from the manifold (green arrows) and lift the rail upwards. You may also want to pull off the rubber u-hose that connects to the pressure regulator. Shown here is the Porsche 996 Carrera motor that was transplanted into the Boxster. As you pull up on the fuel rail, some may stick in the manifold, or some may come out with the fuel rail - it all depends upon a variety of factors.
Release the fuel rail from the tops of the injectors by removing the small, square retaining clips that fasten and secure the injectors to the fuel rail (blue arrow). Use a pair of needle-nose pliers to pull this clip off. It pulls off from the front (it's C-shaped), and should slide off with a reasonable amount of force. This task is performed with the rail still installed on the engine, but is shown out of the car here in this photo for clarity. The inset photo in the upper left shows the fuel pressure regulator removed from its housing (simply slide off the clip holding it in place). The inset photo in the lower right shows the injector once you remove it from the fuel rail. The big, fat o-ring will offer quite a bit of resistance (yellow arrow). The same o-ring which holds the injector into the fuel rail (red arrow) is also the same type that is used to hold the injector into the manifold.
To remove the nozzle o-ring, first cut if off carefully with a razorblade. Be careful not to damage the green plastic tip when you cut through the o-ring. Then, remove the o-ring with a pic, again taking care with the tip. Finally, to get the new o-ring on, you will need to remove the tip. The best method I figured out for removing the tip was to get a small 8-9mm crescent wrench and apply uniform pressure against the tip. However, this still results in some of the plastic on the tip becoming marred. Pressing up with the wrench using a surprisingly large amount of force will make the tip pop off of the injector. At this point, you can attach the new o-ring and snap the tip back on.