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420SE
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Discussion Starter #1
I’m writing this as I could not find any post that delt with what to expect when replacing or cleaning and refitting fuel injectors for a 116 engine in a 420 se sedan. Also moderators note. When searching for this subject I had to wade through lots of other v8 models to get to the specific W126 model.This never used to happen on the old site. Please fix this as it’s a time waster.
So to return ,this is the post I had hoped to find and I hope it helps others who need to do this.
I’ve inlcluded images. It’s a very simple and well designed system as you would expect.
I’ve left the plastic tube that the injector sits in as I’m just doing the injectors for now.
I’ve started on the left side front of engine. I’ve got this feeling I’m only the second human to do this on this engine. The injectors are steel and I thought they would be brass.
I warm her up to operating temp added a squirt of Inox to each bolt. Stopped for a coffee.
Remove the throttle rods and spring and clean out the hex head recess . Now remove the the hex (5mm) bolt, ( this bolt can be very hard to move it’s on tight .This bolt takes the tension off the plastic sleeve fitting, Allen key dose not work here and I used a mini breaker bar.
I moved on to the next one. The 5mm hex key fitted tight . I applied pressure and felt the key tearing into the bolt like it was aluminium!
Ok moved to the next one and same thing , no traction.
Moved on to number four, I’m careful right, and click she moves away nicely.
I will return but first once you have the spring plate off the injector you will see the 12 mm head below the fuel line fitting and thread. Get a spanner or socket on it and turn it just to loosen it. It’s not threaded Looking down you will see the section which has three raised sections . I used a medium slotted screw driver to gently push against the raised section counter clockwise till I could spin it freely and lift the injector and plastic seal out between my fingers. You will see now how the design works. I will continue tomorrow. Images attached. How nice would all of this looked in the original cadmium gold!
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1990 420 SEC
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153 Posts
So far I have replaced 7 injectors. The car is from 1990 and injectors may be original. Number 6 will be the last. That will require removal of idle manifold. I got three screws opened without drilling them so far. Good thing is that screw heads do not break off. On the ones I did not get out I tried to drill a 3.5 mm hole in the middle of the screw. Seems that the core of the screw is harder and drill tends to go to side. After there is a hole in the screw some penetrating oil gets to the thread via that hole. Also tension is relieved by the drilling. What is left of the screw comes off when I drive a Philips screw driver to the head of the screw and twist. I will replace screws with studs, a pile of washers and a nut on those locations where it is possible. As long thread as possible into the manifold and some grease to the threads.
After reading the internet some people like brass injectors and some steel ones. Old ones are steel and new ones brass. Both ones are still available.
 

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420SE
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352 Posts
Discussion Starter #3
Hello Heikkif
Are your injectors the same as mine? I’m interested to know if the plastic seal is the same. Also are you cleaning or replacing the injectors?
 

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1990 420 SEC
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153 Posts
Injectors seem to be the same as on your car. Steel body. I'm replacing them with brass body. They seem to wear out. Mine are not leaking but engine idles better with new ones. The seal in your picture is the same for both injectors. There is a plastic washer at the top of the rubber seal. The rubber seal can be removed if it is oiled between the seal and injector and if the seal is still rubber alike. Injectors come without those seals. Brass injector is 0 437 502 054 and steel 0 437 502 035. This is for KE-jetronic. Those are Bosch numbers. The seal is 1160700077.
I do not have that tester.

Another place for air leaks:
 

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420SE
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Discussion Starter #5
I’m planning on cleaning my injectors with seafoam as they are very expensive here in Australia and our exchange rate.
 

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1991 560SEL
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564 Posts
tip for future: I've found that if the allen bolts (any allen bolts on a car) are very snug, and dont loosen with a moderate amount of force with a hand tool? That using too much slow by hand force will start to strip the head of the bolt. The slow torque torques the corners of the allen head and strips. I've also found that if I grab my cordless impact and use an allen head socket? The shock/impact loosens the allen head bolts immediately with zero stripping. Assumptions are that you clean out the allen head bolt of any debris so that the socket can fit fully into the bolt securely.
 

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1990 420 SEC
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153 Posts
Anything that helps loosening allen screws when needed on this engine without stripping the heads is heaven sent.
 

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Discussion Starter #9
Thanks lesguy.
I’m back on this job today and will set up my impact with the hex head. Fingers crossed.
 

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1986/1990 W126
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13,575 Posts
Stripping these was my worst fear. I used penetrative fluid for at least a week, maybe two. Applied multiple times and allowing the warmth of the engine to help it work.
I bought really nice quality individual sockets to fit the heads. I took my time and all went well.
I got a set of lowish mileage original MB injectors cleaned at an injector specialist place. (Mostly do diesels I think.) No idea what they did, car ran beautifully when finished though.
 

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1989 560 SEC - V-8 Kompressor - 95 E320 Estate
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1,902 Posts
To loosen the hex bolts I make sure the opening is clean then apply a dab of "valve grinding compound" to the tip of the hex tool. Valve grinding compound can be found at most auto parts stores for about $8 a tube. I use it on the large steering wheel hex bolt as they were installed with Loctite at the factory. When you strip one of those out you have a major problem. Mike
 

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1991 420 SEL
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130 Posts
Bigdaddy I was trying to think up a grit that would work and - that's perfect!

Are these bolt heads easily accessable? I often use one of these:

(not mine, no aff etc) as long as I can get to it, get it steady on there and give it a whack with a hand sledge.
 

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'91 560SEC, '98 SL500
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I also stripped several of the Allen bolts as well when I was rebuilding the fuel injection on my SEC. I ended going back in with new stainless bolts and tapped every hole to make sure the threads were whistle clean before proceeding. I'll post some pictures so this thread will be informative for other owners embarking upon this project in the future.
Yasin
 

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Discussion Starter #17
Love to see those images Yasin. Mine is a 1990 and has only now started to play so I recon there is plenty more cars in the pipeline.
 

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Discussion Starter #18
That should be , play up,. Also just revisited the problem and decided check the plugs and...see image. Slotted! I think that’s the problem but will replace and report back.
Yes I did check each plug five weeks ago! Must of missed it.
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420SE
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Discussion Starter #19
Ok every plug has the slot duhhhh. Back to square one. Learnt something though.
 
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