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  #1  
Old 12-22-2006, 11:44 AM
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Join Date: Dec 2006
Location: PA, Southern Chester County
Posts: 8
Question Ignition switch grounded wire? PLEase help!!!

I deaperately need a help with my 500 SEL (1985). The engine died and can not be started. There is no spark when you crank engine . I found that there is no power on fuel pump. Its positive wire is grounded somewhere (no resistance to the ground). Fuel pump relay clicks when you connect battery terminals with ignition key out (I found it by accident ). When I turn ignition key, fuel pump does not run, so engine does not start. Fuel pump runs when I connect it directly to the power. My guess that it must be a short fuse somewhere in an ignition lock. But I can not remove it or test it ! What are steps to do this for this car?

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Old 12-22-2006, 11:53 AM
david s poole
 
Join Date: Mar 2005
Location: dallas
Posts: 1,822
the ignition unit creates a "td" signal when the engine starts to keep the fuel pump running.but you have no spark so no signal.sounds like you need a rebuilt ignition control box[left fender by h/light]not unusual especially when key left on for period of time.without spark no fuel pump.
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David S Poole
European Performance
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4696880422

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1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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  #3  
Old 12-22-2006, 12:04 PM
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Join Date: Aug 2006
Posts: 141
iIgnition short

No spark when cranking and fuel pump shorted to ground is unlikely.
When measuring the positive wire at the pump it must be disconnected at both ends.
The pump gets no power unless engine is cranking or running.
Test the distributor signal generator (green wire) with an a/c voltmeter, plug it in the center and side and crank the engine. You should read .350 a/c volts or greater. If this reading is OK and the cap and rotor are good you need a new,used or rebuilt ignition switching unit.
Post your fix
Mike
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  #4  
Old 12-22-2006, 12:11 PM
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Join Date: Dec 2006
Location: PA, Southern Chester County
Posts: 8
Quote:
Originally Posted by david s poole View Post
the ignition unit creates a "td" signal when the engine starts to keep the fuel pump running.but you have no spark so no signal.sounds like you need a rebuilt ignition control box[left fender by h/light]not unusual especially when key left on for period of time.without spark no fuel pump.
Thank you for your advice I thougt about ignotion unit. I actually tested some voltages on ignition box, but I don't have enugh of documentation about this car. Do you have any information how to test an ignition module on this car? There is a diagnostic socket next to the ignition module. I also was confused with a fuel pump relay when it was powered with ignition key out! Thank you for yor help!

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