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Pelican Technical Article:

Replacing Your Fuel Injectors

Steve Vernon

Time:

4 hours4 hrs

Tab:

$20 to $270

Talent:

***

Tools:

10mm socket, 15mm, (2) 17mm wrenches, 6mm Allen, pliers, flathead screwdriver, oil filter wrench, rags

Applicable Models:

Mercedes-Benz 260E (1987-89)
Mercedes-Benz 300CE (1988-93)
Mercedes-Benz 300TE (1988-93)
Mercedes-Benz 400E (1992-93)
Mercedes-Benz 500E (1992-93)
Mercedes-Benz E320 (1994-95)
Mercedes-Benz E420 (1994-95)
Mercedes-Benz E500 (1994)

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 there is a good chance it is time to replace the fuel injectors. Modern fuel injectors are made of plastic. I do not recommend having them serviced or rebuilt. Older mechanical injectors opened by fuel pressure alone and were 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.

You're going to be working on the fuel system so have a fire extinguisher handy (and know how to use it). 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. 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. It may not hurt to have an assistant around in case there are any problems.

You will need to remove the crossover air pipe before beginning. Please see our article on throttle body removal for further assistance. Note: the throttle body and resonance valve are missing in these pictures. You do NOT need to remove them for this job.

Before you open the fuel system up it is a good idea to relieve the pressure in the system.
Figure 1

Before you open the fuel system up it is a good idea to relieve the pressure in the system. The best way to do this is to remove the fuel pump relay and crank the engine over a few times. This will draw the fuel already in the system out and relieve some of the pressure. The fuel pump relay is located in the upper right side of the engine bay behind the battery. There is a plastic tray behind the battery that you can move out of the way (red arrow).

If your hands are small enough you can reach down in the area between the hood and cowl and remove the fuel pump relay (red arrow).
Figure 2

If your hands are small enough you can reach down in the area between the hood and cowl and remove the fuel pump relay (red arrow). The relay sits tightly in the mount so wiggling it out helps. If your hands are too big you will need to remove the battery first to get at it from the front; of course this means you will need to disconnect the battery to remove it then reconnect it to crank the motor with the relay removed. Please see our article on battery removal for further assistance. With the relay removed crank the ignition on. 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.

Lift the plastic cover off of the wiring harness (red arrow) to expose the fuel rail below (yellow arrow).
Figure 3

Lift the plastic cover off of the wiring harness (red arrow) to expose the fuel rail below (yellow arrow).

Open the cap on the Schrader valve (red arrow).
Figure 4

Open the cap on the Schrader valve (red arrow). Use a small flathead screwdriver and gently press the release valve. It is a good idea to have a rag wrapped around the valve to catch any fuel that will escape.

Cut the zip ties on the wiring harness to give you room to move them (red arrows).
Figure 5

Cut the zip ties on the wiring harness to give you room to move them (red arrows). Use care not to cut any of the electrical lines.

You are going to be opening holes that go into the engine.
Figure 6

You are going to be opening holes that go into the engine. Before you begin get a can of compressed air and blow all the dust and debris away from the injector ports (red arrows).

Use a10mm socket or wrench and remove the single bolt (red arrow) holding the tray in place.
Figure 7

Use a10mm socket or wrench and remove the single bolt (red arrow) holding the tray in place.

With everything loose move the tray and disconnect the wiring from the injectors (red arrows, two shown).
Figure 8

With everything loose move the tray and disconnect the wiring from the injectors (red arrows, two shown). Squeeze the wire clips together and pull the connectors straight off.

Disconnect the vacuum line from the fuel pressure regulator (red arrow).
Figure 9

Disconnect the vacuum line from the fuel pressure regulator (red arrow).

With everything disconnected move the wiring and tray out of the way towards the top of the engine (red arrow).
Figure 10

With everything disconnected move the wiring and tray out of the way towards the top of the engine (red arrow). Remove the dip stick (yellow arrow).

You will need to remove the oil filter lid to get access to the two rear 5mm Allen bolts on the injector rail.
Figure 11

You will need to remove the oil filter lid to get access to the two rear 5mm Allen bolts on the injector rail. Use an oil filter socket or wrench and remove the lid (red arrow). Please see our article on oil and filter changing if you need additional help or would like to change the filter while you are doing this job.

There are two fuel lines attached to the rail.
Figure 12

There are two fuel lines attached to the rail. Use a 15mm and 17 mm wrench to break the first line free and then two 17mm wrenches to break the other line (red arrows). Always support the fitting with another wrench when separating fuel lines.

There are five 6mm Allen bolts holding the fuel rail to the intake manifold and engine (red arrows).
Figure 13

There are five 6mm Allen bolts holding the fuel rail to the intake manifold and engine (red arrows).

Some of the Allen bolts at the front and rear of the fuel rail are difficult to reach (red arrows for example).
Figure 14

Some of the Allen bolts at the front and rear of the fuel rail are difficult to reach (red arrows for example). Always make sure the Allen is well seated in the bolt head before attempting to remove. You do not want to strip these bolts out. If you think they are difficult to remove with a regular Allen, try removing them with an Easy Out.

Pull the injectors and fuel rail straight back on the angle of the injectors and out from the head (red arrow).
Figure 15

Pull the injectors and fuel rail straight back on the angle of the injectors and out from the head (red arrow). They are just held in by the O-rings and you will feel a "pop" when they let go.

Be sure to put a few rags in the open holes in the manifold to prevent anything from falling into the engine (red arrows).
Figure 16

Be sure to put a few rags in the open holes in the manifold to prevent anything from falling into the engine (red arrows). If you drop something into these holes you must get it out before going any further. These holes go directly into the cylinder head and will cause catastrophic damage if left in!

Take the injectors in the rail to your work bench.
Figure 17

Take the injectors in the rail to your work bench. The injectors are held on by metal clips; they can be pried or pulled off the rail (red arrow) using a small screwdriver.

Next, you can remove the injector (red arrow) from the rail by wiggling it out.
Figure 18

Next, you can remove the injector (red arrow) from the rail by wiggling it out. It is just held in by the O-ring at this point. Make sure that the O-ring in the fuel rail (yellow arrow) comes out with the injector. If the O-ring remains in the fuel rail port, use a small screwdriver to remove it, using care not to scratch the port.

': New injectors come complete with new O-rings.
Figure 19

New injectors come complete with new O-rings. Apply a small amount of white lithium grease (red arrows) and reinstall. If you are reinstalling your old injectors make sure to replace both O-rings before installing. Installation is the reverse of removal.



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Comments and Suggestions:
Doug Comments: So I was doing tune-up work and replaced some cracked ignnition parts and the wires..and found a set of flow-matched injectors on EBay very reasonable..and find the part nuber is A0000788623 instead of the A0000788523 which is shown for my year..This seems to match the 97 which I find is the V6 rather than m104...but the only difference is instead of two holes at the fuel spray there are four..the size and electrical plug matches perfectly..Does anyone know what the differeince is, possibly a refinement of the part's design..?? Any reason to not use them? Many charts show cross model fittment for different years..Thanks so much! Ive purchased fuel pumps and new blower motor and relays and...tons of great stuff from Pelican..Excellent source!
November 2, 2016
  Followup from the Pelican Staff: If they cross-fit, using he newer version should be fine. I don't have any specific info on it, the parts specialists may, give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts  
Gary Comments: I have a 1990 300E 2.6, M103 Engine. This artiv=cle is meant to cover my car but the oictures and instructions do not correspond at all. My injectors look totally different and are mounted directly into the inlet manifold - not into a "fuel rail." Each brass injector has its own single O ring and lower rubber seal and sits into a white plastic plastic holder, They are held into the manifold by a metal clip secured by an allen head bolt.
October 20, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 
theo Comments: 1990 benzs are dumping gas into the intake do I change injectors please let me no what to do
June 8, 2015
  Followup from the Pelican Staff: If the injectors are stuck open, yes. Perform a fuel system test, pressure, volume quality and leak down. - Nick at Pelican Parts  
theo Comments: hi guys I check the vacuum hose and found no leaks but when i took off the breather cap I here air coming from the air flow meter an lots of air so I will change the whole thing an hope it works an thanks for your help I am going to take it off a another 300e an see or buy another
May 17, 2015
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
theo Comments: hello nick if there is no vacuum leaks throttle switch is ok then whath eles is to check
May 12, 2015
  Followup from the Pelican Staff: have you confirmed those items are OK? I prefer to test rather than hypothesize. - Nick at Pelican Parts  
theo Comments: hi guys its theo again my 1990 300e benzs idleing up an down and I change new spark plugs and new wires rebuilt fuel distubor new fuel pump and filter new crank sensor new ignition coil its still idleing up and down skiping someone please help me con the o2 sensor cause this or something else
May 9, 2015
  Followup from the Pelican Staff: First, check for vacuum leaks. Once you are sure there are none, check the throttle switch. - Nick at Pelican Parts  
theo Comments: hi guys i have but a new carnksensor in my 1990 300e benzs an it truns over but shuts back off mabe getting too much air from some where on the engine or do i have to change the spark plugs an wries change gas we almost got it
January 9, 2015
  Followup from the Pelican Staff: I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume and quality. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
theo Comments: fire goes to the coil but dont come out itook atest light an test for fire each saide gets fire but it dont go to the dis-cap what shal ido change igntion control moulde or crank sensor or will the safty system or over load relay stop it starting up it was runing fine park in the yard then it just stoped turn over but wont carnk up like its lost mojo please i need help new fuel pump filter new plugs new wires help me get her mojo back thanks
December 5, 2014
  Followup from the Pelican Staff: A test light is not a good way to test primary. You meed to use a scope or graphing multi-meter.

If you have signal to the coil, and it doesn't fire, the coil is faulty. - Nick at Pelican Parts
 
theo Comments: hi im back agian my 1990 300e is not getting fire to the plugs what can i do to fix the problem
December 4, 2014
  Followup from the Pelican Staff: Check if the coil is has power and a signal to fire. - Nick at Pelican Parts  
theo Comments: no the engine do not start wen it trun,s over it not getting eny fire to the plugs no fire comes out of the dis-cap or coil i use a test lite on the coil an it lite up on both wries of the coil dosent comes out of the coil wire at all coil wire is good been change still no crank please help
November 22, 2014
  Followup from the Pelican Staff: Does it have fuel pressure and injector pulse? - Nick at Pelican Parts  
theo Comments: 1990 300 e benzs if it don,t crank can it be the carnkshaft position sensor /coil do have fire getting to it but not comeing out of the coil to the wires
November 15, 2014
  Followup from the Pelican Staff: Does the engine crank as in turn when you try to start it?

I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume and quality. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 
theo Comments: 1990 300 e benzs if it don,t crank can it be the carnkshaft position sensor
November 15, 2014
  Followup from the Pelican Staff: If the engine won't turn, the crank sensor is likely not the issue. - Nick at Pelican Parts  
teo Comments: 1990 merecedes benzs turn over but wont start no spark from coil please tell me what to do it was runing park in the drive way runing fine then it shut off i check spark plugs wires change coil dis- cap not geting fire can it be the elct-moul timeing cain is not gone mite it be the alarm stysem
November 13, 2014
  Followup from the Pelican Staff: Check if the ignition coil has power and if it is being triggered. If it has power and is not being triggered, the module may be faulty. - Nick at Pelican Parts  
theo Comments: how do u chek for fault code in a 1990 300e benzs
September 14, 2014
  Followup from the Pelican Staff: See this thread:

http://www.peachparts.com/shopforum/tech-help/311842-reading-codes-1990-300e.html - Nick at Pelican Parts
 
theo Comments: it starts every time new sparkplugs new gas new fuelpumps new filter but it still stalls wen diving 10min in 15 min pipes are closein in chek for hose leaks none/ i dont no whats rong when i start it it aks lak it skips in idleing then put it drive some times it cuts off carnks back up drive 5 to 10 min shuts off carnks back up
September 14, 2014
  Followup from the Pelican Staff: You will have to check what is missing, like I suggested when it will not start.

Check spark, fuel injector pulse and pressure fuel, volume and quality. Once you figure out what is missing, it will be easier to diagnose.- Nick at Pelican Parts
 
teo Comments: 1990 benzs carnks and drives great for 10/15 min then it stalls out new gas new plugs it ask like its flooding out wont stay ilde please help
September 8, 2014
  Followup from the Pelican Staff: Could be losing spark. I can't help without knowing what is missing from the system when you are trying to start it. When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and pressure fuel, volume and quality. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose.
- Nick at Pelican Parts
 

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