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Mercedes Fuel Injector Replacement
 
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Pelican Technical Article:

Mercedes Fuel Injector Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$675

Talent:

***

Tools:

Torx Set, pliers

Applicable Models:

Mercedes-Benz ML320 (1998-03)
Mercedes-Benz W203 (2001-07)

Parts Required:

New injectors, White Lithium grease

Hot Tip:

Check for flooded cylinders

Performance Gain:

Better-running engine, improved fuel mileage

Complementary Modification:

Replace worn out hoses

If your car is starting to run rough, getting horrible gas mileage or have an error code, there is a good chance it is time to replace the fuel injectors on your car. Modern fuel injectors are made of plastic and we do not recommend having them serviced or rebuilt. Older mechanical injectors opened by fuel pressure alone and where easier to service, newer injectors are made of plastic, need an electronic pulse from the ECU to open and are better replaced than sending them out for service.

A properly working injector will send a precise amount of atomized fuel into the induction system at a designated time. A weak or improperly working injector can do everything from send no fuel, to leak raw, non-atomized fuel into your engine.

If you are going to be replacing your injectors, the first step is to prep the car. I like to tell people to pull out the fuse for the fuel pump 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, also 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 as 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 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.

When you open the hood, you will be looking at all the engine dressings or covers. Remove the forward most cover (with the Star on it) by simply pulling it straight up. Next separate and remove the two plastic air intakes. They are both just friction fits and will pull off. Now remove the main engine cover. There are four clips on it, two that you can see by the vacuum regulators, and two underneath. Pull the cover straight up and off.

The fuel rail is held in place by four bolts and the rubber O-rings on the injectors, but there are a few things you will need to remove first to give you room to work. Begin by removing the larger rubber crossover hose between the vacuum regulators on the front of the engine, along with the small rubber hose that has a Y connector on the passenger side.

Next, unclip the electrical connector by the driver's side vacuum regulator; squeeze the two metal ends together and pull it off.

There is a hard plastic line that runs along the top of the driver's side fuel rail, this is for the EGR purge valve, pull it out of its connectors and set it aside.

There are two emission hoses on the driver's side valve cover you will need to move to give you more room, they just pull straight off. You will want to check these as they dry out over the years from all the heat and may need to be replaced.

Move to the passenger's side and disconnect the single hose there.

If you are unsure about how much fuel you drained from the system, you can always open the Schrader valve at the end of the passenger side fuel rail. Make sure you have some rages handy as there will be some fuel spillage.

Next remove the four Torx bolts holding the rail and injectors in place. You will need an E10 female Torx socket.

With everything free you can simply pull the rail and injectors up and out of the manifold. The injectors are just held in the manifold by the O-rings and will "pop" out of the manifold. Be sure to put a few rags in the open holes in the manifold to prevent anything from falling into the engine. If you drop something into this hole you must get it out before going any further, this hole goes directly into the cylinder head and will cause catastrophic damage if left in!

Remove the electrical connector on the injector. It is a simple push (in the two clips) and pull connector.

The injectors are held on by metal clips; they can be pried or pulled of the rail. Next, you can remove the injector from the rail by wiggling it out, it is just held in by the O-ring at this point.

New injectors come complete with new O-rings. Apply a small amount of White Lithium grease and reinstall.

If you have had an injector that has been leaking heavily it can be a good idea to remove the coils and plugs to drain the combustion area of the extra fuel. While most of the fuel will drain out pass the piston rings, a severely leaking injector can cause hydro lock. It is easy to remove the plugs and can be cheap insurance.

Each coil is connected by a single plug on the harness. Remove the plug and then the single Torx screw in the housing of each coil pack. Unplug the coil from the spark plug and remove. Next, simply remove the plugs and turn the engine over a few times. Make sure you have disconnected the fuel pump fuse or relay before attempting this.

Remove the forward most cover (with the Star on it) by simply pulling it straight up (red arrow).
Figure 1

Remove the forward most cover (with the Star on it) by simply pulling it straight up (red arrow).

Remove the two plastic air inlet connector tubes.
Figure 2

Remove the two plastic air inlet connector tubes. They are friction fits and you can just pull them off.

The top engine cover can be pulled straight up and off.
Figure 3

The top engine cover can be pulled straight up and off. There are four clips holding it on - two by the vacuum regulators (yellow arrows and inserts lower left and right), and two hidden under the cover (red arrows).

Remove the two rubber hoses connecting the vacuum regulators.
Figure 4

Remove the two rubber hoses connecting the vacuum regulators. The large hose pulls away from the rear of the regulators (green arrow) and the small hose pulls off the side connection with a Y-connector on the passenger side (yellow arrows).

Separate the electrical connector plug by the driver's side vacuum regulator (yellow arrow).
Figure 5

Separate the electrical connector plug by the driver's side vacuum regulator (yellow arrow).

Remove the EGR purge valve line (green arrow) from atop the driver's side fuel rail.
Figure 6

Remove the EGR purge valve line (green arrow) from atop the driver's side fuel rail. It just unplugs from its connecting points. The red arrow shows the fuel supply line.

Disconnect the two hoses from the drivers side valve cover to give you more room to work.
Figure 7

Disconnect the two hoses from the drivers side valve cover to give you more room to work. They just pull straight back and off. Note; Check these for cracks and be prepared to replace.

Remove the line from the valve cover on the passenger side.
Figure 8

Remove the line from the valve cover on the passenger side.

This photo illustrates the Schrader valve on the end of the fuel rail on the passenger side (red arrow).
Figure 9

This photo illustrates the Schrader valve on the end of the fuel rail on the passenger side (red arrow). You can use this to drain fuel from the system, but have some rags ready. Note: You can also use this valve to test your system's fuel pressure.

Using an E10 female Torx you can now remove the four Torx bolts holding the fuel rail and injectors to the intake manifold (green arrows).
Figure 10

Using an E10 female Torx you can now remove the four Torx bolts holding the fuel rail and injectors to the intake manifold (green arrows).

Pull the fuel rail and injectors up and out of their holes in the manifold (green arrows).
Figure 11

Pull the fuel rail and injectors up and out of their holes in the manifold (green arrows). Make sure you place a rag over the injector holes (yellow arrow) to stop anything from falling in.

Remove the wiring harness from the injector (green arrow).
Figure 12

Remove the wiring harness from the injector (green arrow). Simply push in the wire on the two ends (red arrows) and pull the plug off.

The injector is held onto the fuel rail by a small metal clip (green arrow).
Figure 13

The injector is held onto the fuel rail by a small metal clip (green arrow). Pull or pry this clip off and wiggle the injector out of the rail.

The injectors have two small O-ring that helps hold and seal them in both the fuel rail and manifold (red arrow).
Figure 14

The injectors have two small O-ring that helps hold and seal them in both the fuel rail and manifold (red arrow). If you are experiencing a vacuum leak it may be one of these O-rings.

If you had a severely leaking injector it is not a bad idea to pull the plugs and turn the engine over a few times to get the gas out of the cylinder.
Figure 15

If you had a severely leaking injector it is not a bad idea to pull the plugs and turn the engine over a few times to get the gas out of the cylinder. Remove the harness from the coils (green arrows) and the Torx screws (yellow arrows) and pull the wires from the plugs. Next you can remove the plugs. Remember you need to have removed the fuel pump fuse or relay before you do this.

This photo illustrates what a coil pack looks like.
Figure 16

This photo illustrates what a coil pack looks like.

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Comments and Suggestions:
rt808 Comments: is the fuel injector same numbering as the firing sequench? In C230 Sports 203 engine. Can somebody tell me where is the #4
Thank You
October 13, 2016
  Followup from the Pelican Staff: Fuel injector numbering is the same as the spark plugs/ cylinder numbers. You can use firing order to locate injectors. - Nick at Pelican Parts  
Troy Comments: I have a 2007 C230 sport. I have a misfire on cylinder 1. I have swapped coils and changed plugs. The vehicle idles fine and only codes after about 2500rpm, then idles rough. If I turn the car off then start it again right away it will run perfect until I reach that higher rpm again. Could this be a possible fuel or injector problem? Any help would be greatly appreciated.
June 14, 2016
  Followup from the Pelican Staff: What is compression? if you have a misfire, the DME may shut down a fuel injector. - Nick at Pelican Parts  
Jason Comments: Thanks pelican. After doing a smoke test I saw I had a bad EGR valve on my C240 rough idle and poor acceleration it was your step by step instructions for removing the fuel injector system that allowed me access to the EGR valve. Could not have done it without you and since I live in California I received the parts from you in one day...Awesome!
April 15, 2016
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Paul Comments: I have a problem with my 98 ML320 , engine cuts out , wait 15 mins. restarts , put in new fuel filter drained and flushed fuel system , OBII codes MAP sensor , replaced . still same problem , no codes , engin runs on starting fluid while spraying . Fuel rail normal pressure still wont start till 15mins.
February 2, 2016
  Followup from the Pelican Staff: When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts  
Abu Faris Comments: I appreciate what you have done. keep up the good work. I am living in a country, Saudi Arabia, where mechanics do things by trial and error.
December 16, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Lee Comments: Getting a misfire on cylinder 5, was told it's a vacuum leak on the intake. I recently had my EGR done so my gas mileage is good, I have also changed the plugs wires and coil. Could it be that I need to do the fuel injectors? Thanks in advance for your help.
December 7, 2015
  Followup from the Pelican Staff: You'll need to test to see what is causing the misfire. I would check spark, fuel and compression on all cylinders. - Nick at Pelican Parts  
Bigdog Comments: Is the electrical connection to the fuel injector right there on the coil pack? I want to check the resistance of my injectors.
March 13, 2015
  Followup from the Pelican Staff: The injectors have separate connectors that attach to the top of them. - Nick at Pelican Parts  
RB Comments: I have a 2001 ML320 low compression in valve #6, heavy gas smell out of exhaust.
February 17, 2015
  Followup from the Pelican Staff: Perform a leak down test to determine if it is a faulty valve or rings. - Nick at Pelican Parts  
bryany Comments: I need some one to tell me what to do on my w203 c320 check engine
October 23, 2014
  Followup from the Pelican Staff: I would start by checking the DME for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
Walter Comments: I am not sure if this is the right place to write, but I need to change the fuel pressure regulator, Do you sell it and do you have some guidance on how to do it?
Thank very much; my car is a 2002 C320
April 11, 2013
  Followup from the Pelican Staff: Sorry, the 2002 C320 does not have a fuel pressure regulator.
roy@pelicanparts.com
 

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