Fuel pump relay

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alf
Posts: 124
Joined: 03 Oct 2008 06:00 pm
Location: Bucharest, Romania

Fuel pump relay

Post by alf » 22 May 2013 07:37 pm

Well, after almost 5 years of running the fuel pump whitout its relay, today i`ve tried to connect it the right way ( years ago i`ve changed the fuel pump position, from under the tank to under the brake cylinder). At the beginning i didn`t thought it will last running on and on but it did. Anyway, can anyone tell me which are the two wires to i have to connect on the relay socket? Under the back seat i have 3 wires, but no + or - on them with or without ignition on. Why? I ask this because the fuel gauge works fine, how the heck? Engine -b200 e.


Gracias. :360:
the early bird gets the worm
`87 B200E on LPG grey GLT aka Time Machine

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Fuse
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Re: Fuel pump relay

Post by Fuse » 26 May 2013 11:23 am

Stock fuel pump relay isn't a normal relay as it's a 5-pole relay and one of the poles is for the RPM signal. The relay won't power the fuel pump unless the engine is turning, so it won't power the pump with just the ignition on, the engine has to be turning also. Fuel gauge meter is just a variable resistor connected to ground so it will work always.

Here's a schematic of the wiring. Fuel pump +12V should be a red wire coming from the relay socket to the back of the car. There's also a fuse in the red +12V line leaving from the relay. The fuse is found from the AUX-fuse box attatched to the left front wing behind the battery. There's also a fuse for the front fog lights in the same fuse box.

http://dl.dropboxusercontent.com/s/fa93 ... _LEJET.png

The schematic doesn't tell what's the color of the chassis ground for the fuel pump but it's usually black or brown. One of the three wires going to the back of the car is for the fuel gauge and the schematic says the color for the fuel gauge wire should be W-Br, which means it's a white wire with a brown stripe, so the pump ground is the one remaining wire, what ever color it is. Pump ground should be always connected to chassis though, no matter the ignition position!


Btw. why did you relocate the fuel pump? The stock pump is designed to be fed directly without any suction resistance as it's not a suction pump, that's why it's installed below the fuel tank in stock form. A separate fuel transfer pump should be installed if the stock pump is used above the tank level. It's not good for the pump to use it as suction pump as it's not designed to work that way. 200-series uses the same type of roller pumps with feed line above the tank, but there's an intank transfer pump in 200-series because of that.



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alf
Posts: 124
Joined: 03 Oct 2008 06:00 pm
Location: Bucharest, Romania

Re: Fuel pump relay

Post by alf » 31 May 2013 09:14 am

Sorry for the late answer: when i had the GLE, at some point i hit a portion with water and melted snow on the highway and that was it! A friend towed me home, and it was owful: winter outside, the water inside the cooling system was cold so i had to drove with a front window down (my window screen slowly became foggy on the inside).
The next day, after a hard battle of trying to start the engine, i saw the fuel pump wires hanging under the car (twisted, rusted). So, i relocate the pump under the brake servo in order to have easy acces on it. When i bought the GLT, i did the same thing. I understand what you`re telling me that it`s not ok for the pump to function that way, but what can i do- should i buy another type? I don`t want to move it back to it`s original place.
Thank you!
the early bird gets the worm
`87 B200E on LPG grey GLT aka Time Machine

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