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Fuel Rail with Injectors Replacement
 
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Pelican Technical Article:

Fuel Rail with Injectors Replacement

Kerry Jonsson

Time:

3 hours3 hrs

Tab:

$25

Talent:

***

Tools:

10mm socket with ratchet. 17mm and 15mm wrench pry bar, pick

Applicable Models:

Mercedes-Benz R129 (1990-98)

Parts Required:

Injector seals, crankcase breather hoses.

Hot Tip:

Run the engine with the fuel pump fuse out until it stalls to reduce pressure in the rail

Performance Gain:

Clean and even flowing fuel injectors

In 1994 Mercedes Benz switched over from a CIS (Continuous Injection System) to an electronic port fuel injected engine. This means an engine control unit electronically grounds the individual injectors that will then spray the correct amount fuel into the engine in very precise amounts. If the injectors are clogged they may not put out the correct amount of fuel and the engine will run rough and you may see your check engine light come on. If you have a gasoline smell from underneath your hood you may have leaking injectors. You can pull out the injectors and change the seals to fix that problem. In this tech article we will go over all the steps to remove and rebuild the fuel rail.

In order to remove the fuel rail you are going to need to remove the engine cover / air filter housing. See our tech article on engine cover removal.

Remove the two 4mm Allen head fasteners (green arrows) that hold the plastic wiring harness cover to the fuel rail.
Figure 1

Remove the two 4mm Allen head fasteners (green arrows) that hold the plastic wiring harness cover to the fuel rail.

ThisPicture illustrates the top of the engine looking down.
Figure 2

ThisPicture illustrates the top of the engine looking down. We have already removed the throttle body and MAF sensor for a previous article but you do not have to remove them to remove the fuel rail.

Remove the two feed and return fuel lines by threading off the 17mm flare fittings (green and yellow arrows) and remove from the rail.
Figure 3

Remove the two feed and return fuel lines by threading off the 17mm flare fittings (green and yellow arrows) and remove from the rail. Here the fuel lines have already been removed. If you have one, use a line wrench on these lines.

Remove the eight fasteners that hold the fuel rail onto the intake manifold.
Figure 4

Remove the eight fasteners that hold the fuel rail onto the intake manifold. Some of the fasteners are 10mm bolts (green arrows). Photo shows the fasteners have already been removed.

Remove the 10mm fastener for the ground wire (green arrow).
Figure 5

Remove the 10mm fastener for the ground wire (green arrow).

Remove the two crankcase breather hoses (green arrows).
Figure 6

Remove the two crankcase breather hoses (green arrows). Pull the hoses straight off to remove. They are probably going to be brittle and break. Order replacements if they do or have new ones on hand before beginning.

With a pry bar or long flathead screwdriver, you can lever up on the fuel rail to unseat the injectors from the intake manifold or you can just pull up on the rail like we did here.
Figure 7

With a pry bar or long flathead screwdriver, you can lever up on the fuel rail to unseat the injectors from the intake manifold or you can just pull up on the rail like we did here. You may want to spray soapy water around the base of the injectors to lubricate the seals and make them easier to come out. Green arrow points to one of the injector seals.

Some injectors may stay stuck in the cylinder head and some will come up with the rail.
Figure 8

Some injectors may stay stuck in the cylinder head and some will come up with the rail. There is a metal clip (green arrow) that holds the injectors to the rail. This may pop off as you try to remove the rail. Keep an eye on the clip if you see the injector stay stuck in the cylinder head. Remember how the clips look when they are properly seated for installation. If needed, you may choose to remove these clips before removing the rail. Then remove each individual injector from the intake manifold. Most time I find the injectors come out with the rail.

Lift the fuel rail up slightly and unplug each injector.
Figure 9

Lift the fuel rail up slightly and unplug each injector. You can do this by squeezing each side of the injector electrical connector spring clip and pulling the connector away from the injector. Do this for all eight injectors.

Pull the fuel rail completely from the intake manifold routing it under the electrical wiring for the sensors and the injectors.
Figure 10

Pull the fuel rail completely from the intake manifold routing it under the electrical wiring for the sensors and the injectors. We have chosen to unplug all the electrical connectors already for photographic purposes. With the fuel rail out use a pick to remove the metal spring clip by sliding it off of the rail. Do this for each injector.

Pull each injector out of the rail.
Figure 11

Pull each injector out of the rail. They have two O-rings that can be replaced. One seals the fuel in the rail (green arrow) and the other seals the injector into the intake manifold (yellow arrow).

Use a pick to remove the injector O-rings.
Figure 12

Use a pick to remove the injector O-rings. If you do not see the injector O-rings look in the fuel rail or the intake manifold where the injectors sit. They may have gotten stuck there. Installation is the reverse of the removal steps. Install new O-rings on the injectors and seat them in the fuel rail. Make sure to position the tab of the injector (green arrow) so it fits in between the gap on the retaining clipsPictured here. Slide the clips on to secure them to the rail. Position the fuel rail on the intake manifold and plug in each fuel injector before bolting down the rail. Remember to route the wiring harness for the sensors at the front of the intake manifold and the MAF. Install the ground wire and fastener. Position the rail so the injectors line up with their holes in the intake manifold. Bolt down the fuel rail and connect the fuel lines. Turn on the ignition key several times without starting to prime the fuel system. You may even want to crank it for a few seconds to build up fuel pressure. Visually verify there is no fuel leaking out in and around the fuel rail. Install any components you may have removed to gain access to the fuel rail such as the engine cover/air filter housing. Start the engine and make sure it runs well.

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Comments and Suggestions:
E Comments: Cleaned my maf on 1992 SL300 and disconnected fuel lines from distributor to injectors. Lost track of where two go. Is there a diagram available showing the routing of the lines.
July 19, 2016
  Followup from the Pelican Staff: I don’t have that info.


I would grab a repair manual. It will have it.
Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Tatastadaiago Comments: rebuilt the fuel distributor was told that was the problem now car has a misfire at low RPM once again i was told it was a vacuum leak been trying to trace all vacuum lines and replace them all since the are so brittle car will start to creep RPM from 650 to 1500 RPM what could be the problem help 92 500SL
July 19, 2015
  Followup from the Pelican Staff: Have you confirmed there are no vacuum leaks? If the misfire happens only at idle, that is a good place to start. - Nick at Pelican Parts  
Bob Comments: My engine is smoking extremley from tailpipe,its not oil smells heavily of gas,changed all spark plugs regaped,still smoking heavily of gas grayish color could this be bad injectors or could,this be fuel pressure regulator,had to change oil because of gas in it you could smell it.THANKS FOR ANY TIPS
June 26, 2015
  Followup from the Pelican Staff: Fuel pressure could be too high, or a leaking injector. I would perform a fuel delivery system test. Check fuel pressure, volume and quality.
- Nick at Pelican Parts
 
whatshapping Comments: RE:1990 SL500; Getting everything back together and have lost track of where the vac line from the bottom of the fuel pressure equalizer runs to!!! HELP. Thanks--Ralph
August 7, 2014
  Followup from the Pelican Staff: Should run to a port on the intake manifold. Look for a small brass nipple. - Nick at Pelican Parts  
Daniel Comments: Lol. Did recheck. Found that I had leaned on the cover for the cruise control linkage and pulled the cable out of its adjustment retainer about a half inch, hence the high idle. Thanks for your response, Daniel
March 30, 2014
  Followup from the Pelican Staff: Thanks for the follow up. We appreciate it.
- Nick at Pelican Parts
 
Daniel Comments: I performed this procedure on my 1996 SL 500 and when I finished I started the car and now my Idle will not drop below 3500. I was wondering if you might have possibilities or solutions. Daniel
March 30, 2014
  Followup from the Pelican Staff: Sounds like a vacuum leak. I would double check your work. - Nick at Pelican Parts  

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