Parts Catalog Accessories Catalog Tech Info Tech Forums
 
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
 >  >
Porsche 911 Carrera Fuel Injector Replacement
 
Bookmark and Share

Pelican Technical Article:

Porsche 911 Carrera Fuel Injector Replacement

Time:

3 hours3 hrs

Tab:

$20 to $600

Talent:

***

Tools:

8mm Torx socket, 10 & 18mm socket, small flat head screwdriver, pliers, jack, jack stands

Applicable Models:

Porsche 996 Carrera models (1999-05)
Porsche 997 Carrera models (2005-08)

Parts Required:

Injector O-rings, new injectors, white lithium grease, zip ties

Hot Tip:

Be extra careful of the plastic injector tips

Performance Gain:

Cleaner, better-running fuel injection system

Complementary Modification:

Replace your spark plugs

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 Carrera 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 or turbo charger 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 super or turbocharger, than 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.

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.

While the fuel injection system for the 1998-2005 (996) Carreras is very similar to the 2005-2008 (997) Carreras, Porsche did make a few changes. The 1998-2005 Carreras use a typical pressure regulator on the fuel line that regulates the pressure and returns unneeded fuel back to the gas tank via a return line. With the introduction of the 997 in 2005, Porsche introduced a returnless fuel system. For the 997 Carreras, Porsche has eliminated the return line by incorporating the pressure regulator into the sending unit in the fuel tank. This way only the quantity of fuel needed by the injectors is pumped to the fuel distributor in the engine compartment. This has the advantage of not having to return heated fuel back to the tank, and helps to further decrease emissions in the fuel tank, helping relieve the tank ventilation system of some of its work. The second change is the introduction of the EV-14 fuel injector. Porsche used the EV-6 injector from 2002 to 2005 (996), but the new EV-14, starting on the 2005(997). The EV-14 allows for better atomization of the fuel and its narrower diameter places its injection point 5mm deeper in the intake runner. All of these changes help with meeting ever increasing emission standards. Plus, as with most things Porsche, it is lighter.

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: Replacing Your Porsche 911 Carrera Fuel Filter) 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. Open the gas cap to help depressurize the 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.

To change out your injectors you are going to need to lower your engine. It is not hard to do and will make this job a lot easier. While I have heard of people changing out their injector with the engine in the car I do not recommend it.

If you are planning on completely removing the fuel rails from the car you will need to remove the two intake plenums to access the fuel line mount at the front of the engine, but if you are just replacing the injectors you do not. See Project 9 if you want to remove both plenums.

Begin by removing the airbox. Loosen and remove the 13mm bolt at the very front of the airbox and the hose clamp holding the boot to the throttle body. You'll also have to unplug the connector to the MAF by squeezing the connector and unclip the harness from its connectors.. Now pull the boot off the throttle body and gently remove the airbox from the engine bay. If you are working on a 3.8 don't forget to remove wire the connection on the back of the airbox for the vacuum resonance valve.

From this point on we will break the article down by models and years.

For the 1998-2005 (996)

On the left side of the engine you will want to clear some room to work. Begin by removing the overflow tube from the coolant reservoir, and the air pump hose. I like to zip tie these together with the other hoses and connection at the back of the engine to keep them out of the way.

Next step is to safely jack up your car (see Pelican Technical Article: Jacking Up Your Porsche 911 Carrera). You do not need to lift the front of the car if you do not want to. Once the car is safely supported in the air, you'll want to place the floor jack in the middle of the engine. From underneath the car, locate the two 18mm nuts on the underside of each mount and remove. Then slowly lower the engine no more than 40mm. Depending on the size of your hands, and how much room you need in the engine compartment, some people just loosen the 18mm nuts, leaving them on the studs, either way make sure you safely support the engine.

Once the engine is lowered and supported, you need to remove the supply and return fuel lines from the rail on the left side of the engine. The supply line is 19mm and the return line is 17mm. Support the fitting with another wrench when loosing, and have some rags on hand as a little fuel may spill out.

After the fuel lines are disconnected you need to reach in and disconnect the wiring harness to the top of the fuel rail. While doing this you will be able to see the rear 10mm bolt holding the rail on, but you will pretty much have to do the one at the front of the engine by feel.

Remove both bolts holding the rails in place. Once the rails are free, you can simple pull up on the rails to remove the injectors from the manifold. They may stick a little so try wiggling them if they don't come straight out.

Move to the passenger side of the engine. On the right side you will need to remove the electrical connections for the oil pressure sender. Mark both leads and slip the connectors off.

Next remove the vacuum line coming out of the fuel pressure regulator and disconnect the wiring harness from the fuel rail.

Remove the 2 10mm bolts and pull the injectors from the manifold.

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 pull the metal securing clip from where the injector mates to the fuel rail. Once removed, you will be able to pull out the injectors. 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 fuel rail 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. 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). This only works on the 996 Carreras. 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.

For the 2005-2008 997

Follow all the steps up to and including removing the air box. On the 3.8 engines be sure to remove the connection on the back of the airbox to the resonance valve.

On the left side of the engine unclip the two coolant hoses and the brake booster pipe on the cross member and lay them off to the side. Remove the plastic lines and the cable plug from the switch over valve.

Loosen the lines for the brake booster. To do this remove the plastic protection, push the holder forward and pull off the line. Put the plastic protector back on right away to keep any dirt or debris out.

Disconnect the vent line for the coolant tank. These are rapid action couplings, press the lugs and pull off the line.

Next step is to safely jack up your car (see Pelican Technical Article: Jacking Up Your Porsche 911 Carrera). You do not need to lift the front of the car if you do not want to. Once the car is safely supported in the air, you'll want to place the floor jack in the middle of the engine. From underneath the car, locate the two 18mm nuts on the underside of each mount and remove. Then slowly lower the engine no more than 40mm. Depending on the size of your hands, and how much room you want to work in the engine bay, some people just loosen the 18mm nuts, leaving them on the studs, either way make sure you safely support the engine.

Now remove the cable duct from the fuel rail. Simply unplug the camshaft positioning sensor, lift up the duct and place it off to the side.

Next you want to remove the two 8mm Torx bolts holding the fuel rail down. Be careful not to drop these down into the engine as they can be a pain to find. Once the bolts are off simply pull the injectors and rail from the manifold as a unit.

Moving to the right side of the engine you want to remove the cable duct. To do this simply, pull the duct off of the fuel rail, unplug the wiring plugs from the injectors and move to the side.

Remove the two 8mm Torx bolts and pull the rail and injectors from the manifold as a unit.

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. Two O-rings seal the EV-14 injectors to the fuel rail and manifold. Always replace the O-rings when servicing your injectors

Installation is basically the reverse of removal. On the 997 you will need to attach the injectors to the fuel distribution rail first, then, insert it into the manifold as a unit. Double-check to make sure that all of the 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.

This procedure is for the 996

Open the engine decklid and remove the airbox.
Figure 1

Open the engine decklid and remove the airbox. Begin by loosening the hose clamp holding the boot to the throttle body (green arrow), then squeeze the tabs on the MAF connector to release it (yellow arrows). Now open the harness holder clip (purple arrow). Pull the oil filler tub up and out of its clip on the airbox. (blue arrow) and finally unbolt the 13mm bolt holding the airbox inside the engine compartment (red arrow) and carefully lift the airbox out of the car. If you have a 3.8 make sure you unplug the connection on the back of the airbox for the resonance valve.

To access the left side fuel distribution rail you will need to remove the coolant tank overflow hose (blue arrow) and the air pump hose (red arrow).
Figure 2

To access the left side fuel distribution rail you will need to remove the coolant tank overflow hose (blue arrow) and the air pump hose (red arrow). I like to gather these hoses and lines and zip tie them together, out of the way.

Safely jack up and support the car.
Figure 3

Safely jack up and support the car. Place a jack under the engine and support its weight. Once everything is safely supported you want to remove the 18mm nuts connecting the engine to the mounts (green arrows). Then slowly lower the engine a maximum of 40mm.

Once the engine is lowered and supported, you need to remove the supply and return fuel lines from the fuel rail.
Figure 4

Once the engine is lowered and supported, you need to remove the supply and return fuel lines from the fuel rail. The supply line is 19mm and the return line is 17mm. Support the fitting with another wrench when loosing, and have some rags on hand as a little fuel may spill out.

Here you can see everything that needs to be removed from the fuel rail (purple arrow) on the left side.
Figure 5

Here you can see everything that needs to be removed from the fuel rail (purple arrow) on the left side. The fuel lines have already been removed (blue arrows). The wiring clips (red arrows) and 10mm bolts (green arrows) are next.

Move to the right side of the engine and remove the electrical connectors for the oil pressure sender (blue arrows), the clips holding the wiring harness (green arrows), the vacuum line to the fuel pressure regulator (red arrow) and the two bolts holding the rail (purple arrows).
Figure 6

Move to the right side of the engine and remove the electrical connectors for the oil pressure sender (blue arrows), the clips holding the wiring harness (green arrows), the vacuum line to the fuel pressure regulator (red arrow) and the two bolts holding the rail (purple arrows). Then just wiggle the injector out of the manifold.

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).
Figure 7

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.
Figure 8

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 Picture 9:mm 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. This procedure is for the 997

Open the engine decklid and remove the airbox.
Figure 9

Open the engine decklid and remove the airbox. Begin by loosening the hose clamp holding the boot to the throttle body (green arrow), then squeeze the tabs on the MAF connector to release it (yellow arrows). Now open the harness holder clip (purple arrow). Pull the oil filler tub up and out of its clip on the airbox. (blue arrow) and carefully lift the airbox out of the car. If you have a 3.8 make sure you unplug the wire connection on the back of the airbox for the resonance valve.

On the left side of the engine unclip the two coolant hoses and the brake booster pipe on the cross member and lay them off to the side (blue arrows).
Figure 10

On the left side of the engine unclip the two coolant hoses and the brake booster pipe on the cross member and lay them off to the side (blue arrows). Remove the plastic lines and the cable plug from the switch over valve between the intake runners (yellow arrow). Loosen the lines for the brake booster (purple arrow). To do this remove the plastic protection, push the holder forward and pull of the line. Put the plastic protector back on right away to keep any dirt or debris out, then disconnect the vent line for the coolant tank (red arrows). Check for slack in your wiring going to the O2 sensors on both sides, and if it looks like it will be tight disconnect the wiring (green arrow).

Safely jack up and support the car.
Figure 11

Safely jack up and support the car. Place a jack under the engine and support its weight. Once everything is safely supported you want to remove the 18mm nuts connecting the engine to the mounts (green arrows). Then slowly lower the engine a maximum of 40mm.

To remove the left side fuel distribution rail you will first need to remove the switch over valve (red arrow), push in the metal wire and pull the plug out, remove the plug from the camshaft positioning sensor (blue arrow and insert lower left).
Figure 12

To remove the left side fuel distribution rail you will first need to remove the switch over valve (red arrow), push in the metal wire and pull the plug out, remove the plug from the camshaft positioning sensor (blue arrow and insert lower left). Now you can slide the wiring harness duct off of the rail. Remove the two 8mm Torx bolts (yellow arrows) that hold the fuel distribution rail to the manifold and pull the injectors and rail from the manifold as a unit. Remove the plugs from the injectors and set the wiring duct aside

13
Figure 13

This photo shows how the wiring duct is connected to the fuel rail (blue arrow), the electrical plugs to the injectors (green arrow), and how the injectors sit in the manifold (red arrow)

On the right side of the engine remove the wiring harness duct from the fuel rail by simply pulling it up.
Figure 14

On the right side of the engine remove the wiring harness duct from the fuel rail by simply pulling it up. It is held in place by plastic clips (blue arrow), unplug the wiring plugs from the injectors (green arrows) push up on the wire clip and pull the plug out, and set the harness and duct aside. Unbolt the two 8mm Torx bolts holding the rail in place and pull the rail and injectors from the manifold as a unit.

The metal clip (blue arrow) can be removed with a small screwdriver or needle nose pliers.
Figure 15

The metal clip (blue arrow) can be removed with a small screwdriver or needle nose pliers. There are two O-rings that need to be replaced when you remove the injectors, one is shown (red arrows) and the other is hidden by where it sits in the rail. Green arrow shows where the wiring plug goes. After servicing or replacing your injectors, build your injectors onto the rail first, making sure the sheetmetal clips engage correctly and reinstall the rail and injector back into the manifold as a unit. The rest of the installation is the reverse of removal.

Bookmark and Share
Comments and Suggestions:
bruceb Comments: I have a std 2001 996 Carrera and looking to replace the injectors. I am seeing 440cc injectors much cheaper than the standard 290cc injectors. Would it hurt to install these higher flow without any other change to the engine.
January 7, 2015
  Followup from the Pelican Staff: I don't see the benefit in doing so, so I would avoid it. It can cause issues without software adjustment to the DME. - Nick at Pelican Parts  

  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: Sat 12/3/2016 02:32:33 AM