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Relays draining my battery
speedyxjs - 9/10/09 at 07:35 PM

My battery had been loosing its charge at a rate of .2v per day. To diagnose it, i pulled all the fuses and unplugged the ECU, no change, so i automatically thought it must be the alternator.

Not so, yesterday i pulled the fuel pump relay (the only one i have) and checked it this morning and it hadnt changed.

I have never wired a relay before but must have done something wrong.

The one thing i am not sure about is that it clicks when i unplug or plug it in. Does this mean i have the wires the wrong way round?

02GF74 - 9/10/09 at 07:40 PM

yep - does sound like it iswire in wrong and symptoms ofbattery draiing implies the coil is always on - when you remove it, you hear the click as the contact move since you have removed power to the coil.

what a the pin numbers on the relay?

and how have you wired it?

note that some relays have a built in snubber dioe so the coil needs to be wire in one particular way.

Dusty - 9/10/09 at 07:45 PM

The only way it can click when you unplug is if that action cuts the switching current. But you're not saying it's running the pump all the time. So relay switching must be active all the time. Switched circuit to pump presumably has ignition live supply or the pump would run all the time. What have you got switching the pump relay on/off at present?

Rod Ends - 9/10/09 at 07:45 PM

fuel pump relay would be controlled by the ECU and would normally be off until ignition switch is on.
(and usually goes off after a few seconds if the engine isn't running)

Dusty - 9/10/09 at 07:54 PM

Agreed, that's how it works in mine but i'm not the one with the problem and I have seen other methods of switching the relay. Need to know how it's switched on this car.

BenB - 9/10/09 at 08:03 PM

Yup. Def sounds like your relay is constantly on.....

speedyxjs - 9/10/09 at 08:22 PM

Fuel pump is not on all the time, and the relay works as it should.

I havnt wired it up to the ecu as i thought it would be simpler to bypass the ECU.

Dusty - 9/10/09 at 09:55 PM

Your relay probably has terminals numbered 85 and 86 for the switching circuit. One should be powered by an ignition live and the other earthed. It also has terminals 30 and 87 for the switched circuit. Connect 30 to a battery live and 87 to the pump. Circuits should be fused. You should at least have a dash switch in the ignition live to 85. There should also be an automatic means of cutting the power to the pump in the event of a crash. Insert oil pressure or motion activated interupt relay between 87 and the pump or use the ECU which also has this function.

[Edited on 9/10/09 by Dusty]

02GF74 - 10/10/09 at 07:53 AM

quote:
Originally posted by Dusty
Your relay probably has terminals numbered 85 and 86 for the switching circuit. One should be powered by an ignition live and the other earthed.


to play it safe, wire 86 to 12 V, and 85 via switch to ground in case there is snubber diode fitted, like this:

MikeRJ - 11/10/09 at 10:56 AM

quote:
Originally posted by speedyxjs
Fuel pump is not on all the time, and the relay works as it should.

I havnt wired it up to the ecu as i thought it would be simpler to bypass the ECU.


You should wire it to the ECU, the whole point is that the ECU will only let the pump run when the engine is running.