Author Topic: fuel pump jump relay  (Read 1387 times)

rumb

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fuel pump jump relay
« on: 15 August 2016, 01:22 PM »
I received back my fuel distributor and it said to run the fuel pump for an hour with supply and return lines connected.  I have gathered that I need to jump pins 30 and 87a to do so.  There are 3 relays in my fuse box, I suppose I just try them all until I find the right one? Do I need the key on pos 1 or @ and will this hurt anything else leaving the ignition on this long?
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

rumb

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Re: fuel pump jump relay
« Reply #1 on: 17 August 2016, 09:01 AM »
I'll answer my own question.

Put 5 gallons gas in and then found my fuel pump was DOA anyway.

I plan on hooking up my 12V power supply directly to the terminals on the pump with the key off.  Then I dont have to mess with anything else.

'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

w116john

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Re: fuel pump jump relay
« Reply #2 on: 17 August 2016, 01:36 PM »
hi

i think if you leave the key in position 1? you could damage one of the ballast resistors, as its not supposed to be on all the time just when starting.

i am sure people here have swopped a fuel distributor, i would be surprised if you had to run it for an hour. i am going to change mine in the near future so i am interested to see how you get on.  i have a spare and its the only part of the fuel system i have not changed, in search of a cure for my warm start issues.

all the best

polymathman

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Re: fuel pump jump relay
« Reply #3 on: 17 August 2016, 03:14 PM »
Sorry to take so long with this reply...

In the photos I have marked the location of the fuel pump relay and shown a simple jumper I made from parts on an old harness. There is white paint I put on the socket of the relay to show me where to connect the jumper.

If running pump for a while, I disconnect one wire to the coil and the one wire each to the ballast resistors. Key is in ON position.
190sl 1957 rusting away
250S 1968 long gone
280SE 1976 got hit, parts
280SE 1979 running fine
C320 4Matic 2005 for wife -Mercedes after MIT

rumb

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Re: fuel pump jump relay
« Reply #4 on: 17 August 2016, 03:36 PM »
Thanks for the info, those are great pictures!
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

ortolani

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fuel pump jump relay
« Reply #5 on: 11 March 2020, 06:08 PM »
Hi,
Of which Mercedes is this relay / fuse box?
Thanks in advance.