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Pelican Technical Article:

Fuel Injector Replacement

Time:

3 hours3 hrs

Tab:

$300

Talent:

****

Tools:

6mm Hex bit socket, 13, 15, 17, 19mm wrenches, screwdrivers, bolt extractors

Applicable Models:

Mercedes-Benz W210 (1996-03)

Parts Required:

Fuel injector, seals

Hot Tip:

get a set of bolt extractors.

Performance Gain:

better MPG

Complementary Modification:

Replace fuel pressure regulator

Inside each fuel injector is a small needle valve called a pintle valve that tends to wear down due to repeated cycling. As it wears, it can cause fuel to leak between the valve and the sealing surface. Sometimes, fuel injectors can be cleaned; restoring performance and fuel economy back to stock levels. This is done by ultrasonic cleansing, using sound waves to break up the small bit of dirt and corrosion on the pintle valves. If the injectors are beyond cleansing, then replacement is your only option.

In this article, I will go over the steps involved with removing and/or replacing the injectors on your W210 Mercedes-Benz with a M104 engine. Removing the injectors is a bit challenging but can be accomplished by the do-it-yourselfer with a few pointers we've learned by doing this job.

The most important step in this job is to disconnect the battery. We are working around GASOLINE. It is flammable. It is very easy to ignite gasoline with only a small short circuit. Be safe and remove the 11mm bolt holding the battery terminals disconnect together in front of the rear right seat.

Begin by removing the MAF sensor assembly and also the intake plenum running across the top the engine. This is held on by three 10mm nuts on top of the valve cover. Release the clips on the MAF sensor to remove it from the airbox. You'll also need to loosen the hose clamp holding the upper intake plenum to the throttle body. The clamp itself is located in a tight space. A universal joint socket makes this job much easier. Once the hose clamp is loose, pull the whole intake plenum assembly up and off the valve cover.

Once removed, we will need to relieve the pressure in the fuel system. It's best to wait a day or two without running the engine before you do this job. This is for two reasons: You want to have the engine cold and also to help bleed off some of the pressure in the fuel system. To completely bleed off the pressure, you'll need to remove the metal cap over the Schrader valve in the center of the fuel rail and cover it with a disposable shop rag. Use a screwdriver to press the Schrader valve in. The rag will soak up most of the fuel that will spray out of the valve. Use caution when doing this as you will be working around raw gasoline.

You may be able to bleed off the pressure in another manner by waiting until the car is very low on gasoline and simply run the engine until it runs out of gas. Additionally, you may be able to remove the fuel pump relay achieving the same effect the pump will not deliver fuel to the engine, although this may trigger a check engine light. Its easier to just press the Schrader valve in and be ready to soak up any raw fuel that may come out. Be sure to have a fire extinguisher nearby just in case and wear goggles. Be sure to dispose of a gasoline soaked rag in a metal container and work in a well-ventilated area.

The next step is to disconnect the fuel feed and return lines near the center of the line. Use a 17mm wrench and break loose the two connectors on the rubber fuel lines while counter holding the nuts on the metal fuel rail. It's a good idea to have a rag underneath the fuel line connections to catch any fuel that spills out.

Now we will need to remove the fuel rail from the engine. This is where the job gets somewhat difficult as the fuel rail is held on by five of the 6mm Allen head bolts that also hold the intake manifold to the engine. I've found that it is very difficult to reach these bolts head on with an Allen wrench or even a hex bit socket. It should also be noted that in our case, three of the bolts were stripped out internally. This necessitated the use of what is called a bolt extractor. This is a nifty little tool that grips the outside of the bolt head and applies more force the more you turn it counter-clockwise. I'd also recommend you change the bolts to a conventional hex head to make re-assembly easier.

Don't forget to also remove the 5mm Allen screw holding the dipstick tube to the intake manifold. This will make access to the bolt a little easier.

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 usually 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:019-997-13-48 for many Mercedes cars). This should be done anytime the injectors are out of the car.

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.

Begin by removing the upper air intake tube that runs along the top of the valve cover.
Figure 1

Begin by removing the upper air intake tube that runs along the top of the valve cover (purple arrow). See our article on replacing spark plugs for more info. Once removed, pull the black plastic cover off the valve cover (green arrow).

Remove the cap covering the fuel pressure test port (green arrow).
Figure 2

Remove the cap covering the fuel pressure test port (green arrow).

Place a rag next to the Schrader valve inside (green arrow) and use a small screwdriver to press the valve down.
Figure 3

Place a rag next to the Schrader valve inside (green arrow) and use a small screwdriver to press the valve down. This will bleed off any residual pressure in the line.

Disconnect the two 17mm fittings hold the feed and return lines to the fuel rail (green arrows).
Figure 4

Disconnect the two 17mm fittings hold the feed and return lines to the fuel rail (green arrows). It's a good idea to have a rag underneath as some fuel will probably spill out. You'll also need to counter hold the nuts built into the rail using another wrench (yellow arrows).

Now disconnect the electrical connectors to each fuel injector by squeezing the two tabs together (green arrows) and pulling the connector off.
Figure 5

Now disconnect the electrical connectors to each fuel injector by squeezing the two tabs together (green arrows) and pulling the connector off.

It's very difficult to show the locations of the 6mm bolts that hold the fuel rail to the intake manifold, So I've included thisPicture to demonstrate with the fuel rail removed (green arrows).
Figure 6

It's very difficult to show the locations of the 6mm bolts that hold the fuel rail to the intake manifold, So I've included this picture to demonstrate with the fuel rail removed (green arrows). Take your time as these bolts can be very difficult to remove.

Now cut the zip ties holding the wiring loom to the fuel rail, pull the loom free and pull the fuel rail up and out of the intake manifold.
Figure 7

Now cut the zip ties holding the wiring loom to the fuel rail, pull the loom free and pull the fuel rail up and out of the intake manifold.

Set the fuel rail in a vise and remove the small clips that secure each injector to the fuel rail.
Figure 8

Set the fuel rail in a vise and remove the small clips that secure each injector to the fuel rail. A small pick helps to do the job as shown here.

Pull each injector up and out of the fuel rail.
Figure 9

Pull each injector up and out of the fuel rail. You may need to use a small screwdriver to help pry it out. Check the inside of each port on the fuel rail and see if the O-ring has remained inside. If so, remove them and throw them away. Carefully pull the O-rings of both ends of each injector (green arrows).

Once you have had the injectors cleaned or replaced, fit a new O-ring to each end before fitting them back into the fuel rail.
Figure 10

Once you have had the injectors cleaned or replaced, fit a new O-ring to each end before fitting them back into the fuel rail.

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Comments and Suggestions:
michelle Comments: how often should the fuel injectors be changed or replaced. My husband is replacing the intake manifold on his 2006 E350 with almost 140K miles. He wants to know if he should go ahead and change out the injectors since he has to remove them anyway.
June 25, 2016
  Followup from the Pelican Staff: Usually only replaced if they are giving trouble. As the fuel and tip design keeps them clean and functioning. - Nick at Pelican Parts  
smartchoice Comments: when my engine is revved the fuel injector nozzles current dims and dies off....please what can be responsible? It idles wonderfully but refuses to rev or move beyond 20km/hr. What can cause such electric current fluctuation at the fuel injector nozzles?
March 29, 2014
  Followup from the Pelican Staff: COuld be low supply voltage or a faulty injector driver. - Nick at Pelican Parts  

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