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  #1  
Old 03-18-2017, 04:44 PM
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500 sec fuel pump problem

hello,i have a 1985 mercedes 500 sec and there is no power to the fuel pump and i have 3 different fuel regulators (all used)that i have tried, none does the job ! do you think it could be something else or maybe all 3 are bad ?
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  #2  
Old 03-18-2017, 05:22 PM
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you know there is a relay for the fuel pumps ?, its in the fuse box
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  #3  
Old 03-18-2017, 05:43 PM
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The engine also has to be revolving for the fuel pumps to run in this era of vehicle. They don't have a "prime" cycle like the later cars do. You must have the engine running, or rolling on the starter to have voltage to the pump.
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Old 03-18-2017, 06:05 PM
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yes i said regulators i should have said relays, and yes i did have another guy crank the motor while i was checking, thanks, keep em coming
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  #5  
Old 03-18-2017, 07:42 PM
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You can start by checking power and ground at the relay, you should be able to remove relay and bypass by jumpering power to pumps from that point, if pumps run next you need to check if engine run signal is being sent to relay
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Old 03-19-2017, 08:39 PM
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and how is that done ? the signal to the relay
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Old 03-19-2017, 08:47 PM
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With volt meter , ill get you pin location numbers, I have Mercedes diagnostic manuals
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Old 03-21-2017, 10:17 AM
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If you remove the relay and jumper pin 7 to pin 8 circuit the pumps should run, pin 10 is rpm input or td signal, pin 9 circuit 15/key on to coil , pin 11 ground,pin 12 crank input from starter ,these are all you need to be concern with at the moment
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Old 03-22-2017, 03:41 PM
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thanks i will give it a go
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