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  #1  
Old 06-12-2002, 12:59 PM
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How do I test the amperage draw of fuel pump?

I have a single fuel pump system and I understand that the fuel pump draw should be 8 amps or less to prevent burning out the relay. I have a multi-tester meter that I know basics on how to use. I would like to measure the pump's resistance. My problem is I am a dummy and do not know where to place the two probes of the tester in order to take the measurement. I don't want to fry anything. Please help.
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  #2  
Old 06-12-2002, 01:15 PM
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The fuel pump is powered through the fuel pump relay pin 87.

On my 86 300E the relay is behind the battery and a black flap. If you remove the relay and measure pin 3 from left (viewing from front of car) on the first row - compared to ground, you would get the fuel pump resistance. (not sure if you'd get anything reasonable though)

Here's a picture of the different relays found behind the battery with their bottoms up...

Klima relay (top left)
Fuel Pump relay (bottom left)

and the 'lil one to the right is the OVP (overvoltage protection relay.

This is how they're found behind the battery too.

If you want to measure amperage you'd want to series the instrument with the fuel pump and pin 87 on the relay...which will be a bit tricky...
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99 W210 E220 cdi sedan automatic (248.000 km) 210.006
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  #3  
Old 06-12-2002, 02:33 PM
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Amuso, thanks for your reply but I am still confused. In my car the fuel pump relay is located at the rear end of the fuse compartment under the hood (126). I can pull the relay and read the numbers for the various pin locations. Now where do I place the two probes from my tester? Do I place one in the 87 pin hole? If so. where does the second probe go?
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  #4  
Old 06-12-2002, 03:17 PM
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The following post may help. Read thru all of it:

300E won't start. Fuel pump? How to check??

Lots more on this subject in the archives. Use SEARCH facility.
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  #5  
Old 06-12-2002, 05:30 PM
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Ups forgot that part...

That post by Mike pretty much explains it.

Probe between 30 and 87 for amperage,
Probe between 87 and grounding (or 31) for resistance...
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  #6  
Old 06-12-2002, 11:38 PM
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Mike and Amuso thanks for the help. My fuel pump amperage is 6.7A so it checks out OK. Measurement was made at the 30 and 87 pin sockets.
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