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1992 Nissan 240sx & 1984 Mercedes Benz 500SEL
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12 Posts
Discussion Starter · #1 · (Edited)
Hi guys, I'll start off by introducing myself. My name is Anthony and I was just given a 1984 500SEL for free by a neighbor. Even though it doesn't run I couldn't pass the offer up because the interior is immaculate. Anyway, I've been arouind the import scene for about 5 years now messing around with 4 banger turbos and fuel injection. I've got a great understanding of FI systems and have done many 4 cylinder motor swaps and regular maintanence. I have a good understanding of how a motor works and runs, but when it comes to bigger motors I'm short of knowledge. So here is the deal with the new benz...

When I first got the car home and off the tow truck I popped the air box apart and cleaned the inside out. It had a bunch of nuts and shells sitting in there due to the time it has been sitting. After cleaning it I got some fresh gas in the tank and went to start it. After cranking it for a little bit it felt like it was trying to turn over, but wouldn't stay firing. I ran to the closest auto parts store and grabbed some starter fluid. When I tried starting it with the fluid it would keep running, but not clean at all. It seems like a have a fuel issue like the pump or relay. I just want to get her running so I can wash her and clean her up a bit. Any ideas or advice would be greatly appriciated. :thumbsup:
 

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1992 Nissan 240sx & 1984 Mercedes Benz 500SEL
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12 Posts
Discussion Starter · #4 ·
Well damn I feel dumb now. Do you happen to know if the fuel pump is manual or elec?

Haha I'm just very new to the Mercedes world and haven't really had the time to mess around with the car too much.
 

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'88 560 SEL , 01 540i
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301 Posts
I wonder if those nuts and bolts you saw might actually be from the mechanical injection pump. If that's the case you may be looking a new injection pump.
 

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1985 500 SEC EURO AMG/LORINSER; 1988 560SEL, 1995 S500 Sonderschutz
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3,680 Posts
The Airbox on these cars does look a lot like a carburetor... Are you sure it's not just the Airbox? There should be a filter in there. It has a black hose leading to it from the grille. It is silver and has a mercedes logo on it...
 

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2005 W215 CL500
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3,924 Posts
I wonder if those nuts and bolts you saw might actually be from the mechanical injection pump. If that's the case you may be looking a new injection pump.

He said nuts and shells.. Squirrels !!!!!!!
 

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1992 Nissan 240sx & 1984 Mercedes Benz 500SEL
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12 Posts
Discussion Starter · #9 ·
Yeah there arn't mechanical nuts and bolts... more like squirrel treasures.

Yup I definitely thought something was weird about the so called "carb" my neighbor showed me. This makes my life a whole lot easier. As for my starting issue, when I turn the key to ON I can't hear the pump priming so this leads me to believe it is the pump that is bad. Is there a correct way to test the relay first because I don't want to have to replace both if not nessecary??

Sorry for my misinterpretation. I was told one thing by the original owner and just went by his word. It is definitely an airbox now that I think about it.
 

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1986 Euro 300SEL
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2,151 Posts
As for my starting issue, when I turn the key to ON I can't hear the pump priming so this leads me to believe it is the pump that is bad. Is there a correct way to test the relay first because I don't want to have to replace both if not nessecary??
Have you read through the archives? There's lots of info on this topic that may help you. Having said that, I'd try one easy thing first. You can pull out the fuel pump relay and jumper the pins (search archives for the correct ones), that will bypass the relay and make the fuel pump work at all times. If it doesn't, you have a fuel pump problem. If it does work, see if it will start and run. May be the relay. You can also do a fuel test to see how much volume you get - should get at least a liter in 30-40 seconds. Again, this info is in the archives. If the car sat for a long time it may have gummed up the pump(s) and filter causing flow issues.
 

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1992 Nissan 240sx & 1984 Mercedes Benz 500SEL
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Discussion Starter · #13 ·
I appriciate the input guys. I'm new to the benz, but not to the forum world so I will definitely start my search. After I get it running I'll clean her up and take some pictures. The guy I got it from just replaced all the leather on the interior so it is definitely a worthy project.
 

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2019 Hyundai Elantra, 2005 Chrysler Town & Country, 1999 GMC Yukon
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1,660 Posts
Yeah, with the air box on it does look carbureted.

There is a sticky with info on the weird mechanical/electronic FI system our cars have. Read up on it and you'll be miles ahead.

Welcome to the forum! You came to the right place!
 

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1992 Nissan 240sx & 1984 Mercedes Benz 500SEL
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12 Posts
Discussion Starter · #15 ·
Alright so I got some more time the other day to look at what was going on. I tested the relay by jumping slot 7 and 8. Still didn't start up, but I could hear the pump when I listened back by the rear. There ended up being a small fuel leak in the inlet line between the tank and pump. Nothing big enough to cause it to no start though. I took the air box off the motor to get a better look at the intake manifold and search for vacuum leaks and what not. The spark plug wire look new and everything look in place, but she still won't start. I also test the fuel distributer by feeling pressure when I pushed the throttle body like mechanism down. It easily would slide right back into place after I pushed it. What are some more common problems in getting these things to run?? Its been sitting for multiple years, but it wants to turn over all the way.
 

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When you jumper the pump do you hear gas course thru the fuel lines leading to/from the fuel distributor. It is loud enough to hear if you listen by them. When pressing on the air metering plate you should feel a distinctly different backpressure with the fuel system pressurized. There will also be a slight sizzling noise when it is injecting. If it runs with starter fluid it will run if you manually inject either by jumpering the cold start valve or (not a good idea due to possible backfire) pressing on the air metering plate.
 

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1992 Nissan 240sx & 1984 Mercedes Benz 500SEL
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Discussion Starter · #17 ·
Well I've been traveling in Europe and so busy with my other projects I really haven't gotten around to messing with the benz recently. I got another two nissans and recenly came across a 92 seadoo jet ski so I've been super busy. I'm finally going to go back out and try to get her started. I recenly bought a new fuel filter and I'm gonna throw some high octane new gas in there to burn the old gunk through.

I know its been a while since I started this thread, but so many things have come up. Any other things that usually stop these things from starting??? I might just put some new plugs in there just for the hell of it.
 
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