My 1984 Mercedes 500 SEL won't start.

My wifes 1984 Mercedes 500 SEL won't start. It turns over until battery dies I tried jumpstarting it just turns over any HELP PLEASE? THANKS

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Fuel pump relay is my suspect in your case. I had a 380SE so I do know all about that car you got.
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Tiger wrote:

Do you know how to check it? Thanks
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If you have a service manual, you can pull out the relay and simply jump two terminals to power your fuel pump temporarily.
Just look at the relay... it will say "kickdown" on it and then look at the date stamped on the side of it... If it is the same year as your car, you need to change it.
Otherwise, if you do have technical knowledge, you can take it apart and reflow key joints and clean the relay contacts.
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Tiger wrote:

Thanks I will look at tomorrow. Thanks
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Tiger wrote:

I looked the date was 2002 if I want to jumper do I do it with relay out? It looks like 7 to 8. Thanks
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When you jumper it, it would be with the relay out... since you said 2002... I don't suspect the fuel pump relay... unless it is a rebuilt unit.
If you can start the car with it jumpered, then you know it is the fuel pump relay.
There is another culprit in your case... that would be the overload relay... the one with red fuse on the top.
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Tiger wrote:

How can you tell if that is Bad. Thanks
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Two person job... have wife sit in car and turn ignition to 'on' without trying to start car.
You would be at the fuel pump... put your hand on it, if the pump runs for a few seconds, then it is good.
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Tiger wrote:

I will try that tomorrow Thanks for your help. I went ahead and ordered a overload relay I did a little investigations and it sayed mey idle weird and it was doing that before also. Thanks Again
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Tiger wrote:

I jumpered the terminals I heard something pickup on the motor,however it did not start.Also if the overload relay is bad can that cause the motor not to start? All help highly appreciated.Thanks
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Overload relay when the fuse is blown will allow you to crank engine over but car will not start.
Another possibility for you is crank position sensor. Do you have spark when turning engine over? If no, then this might be it. If yes, then it would be something else.
Another thing to check is the idle control valve... the tubular electrical thing in the front top of engine that have a connector on the front and two tube in 90 degree in the rear... take it out and clean out the internal tube area... spray it out clean with carb cleaner... then put a touch of WD40 in there. This is also another culprit why engine won't start too. If you need one, I got one for sale. New aftermarket unit.
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Tiger wrote:

Okay Thanks.
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Tiger wrote:

Hey Tiger I tried the overload relay and checked the fuel pump in the back and it was making a noise like it is working. I don't seem to have any spark at the Distributor cap from the coil. I looked in my cd about the car said it could be the switching unit whatever that is. I had to much voltage from the coil terminals and it said to replace switching unit any thoghts on that. Thanks
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It is possible the ignition control module (switching unit) may be bad... but considering how old the car is, I would suspect the crank position sensor. Look in your CD about this crank position sensor... without this sensor, there would be no spark.
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Tiger wrote:

Hey Tiger it was the switching unit I ordered one off Ebay and I installed it today and the Car started right up. I'm very happy the cd was correct. Now I just need to quiet down the brakes. Thanks For your help.
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I am glad you solved the problem. Most people would be frustrated by now and give up, but you kept going. That's great and keep doing it.
As for the brake, start another topic and I will help as well. After all I did own a W126 for 11 years. Alot can be improved in brake with just replacement parts.
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