Hi, my mates subaru is having issues with the alarm. He had it removed but is constantly having fuel pump cut issues. We assume its something to do with the wiring of the old alarm. He has tested the fuel pump by running a wire straight to the battery and it seems to work fine. Whats the consequences of hard wiring the fuel pump direct to the battery with a fuse and a on/off switch. Apart from the hassle of manually switching the pump on and off, could this be a temporary fix!
mechnificent,
Jan 24, 8:24am
Have you checked the fuel pump relay!
mechnificent,
Jan 24, 8:25am
if you have a crash the fuel could keep pumping and be a fire risk.
pge,
Jan 24, 8:29am
I would suggest running the wiring to the pump through a fuse that is active only when the ignition is "on".
Then you have the security of knowing that, when the ignition is off, so also is the pump - it is also fuse-protected.
Good luck.
Spelling edited
2lo4ho,
Jan 24, 8:33am
havnt checked the relay at this stage. may sound stupid but i wouldnt know how to check it to be honest. hes not got much cash so looking to fix it as free as possible. i can easily wire in a fuse and switch but i wouldnt know what to look for when it comes to relays. hes happy to hard wire it, just confirming it wont do any more harm
bigfatmat1,
Jan 24, 8:51am
its not really a good idea to do it. I would check the multi plug under the rear seat for burnt connections. as this is a very common problem and gives your symptoms fuel pumps are wired to go only when engine is running this is the safest way to have things the relay is up above fuse boxtowards top of dash and is of a tin can type on most subarus and is trigered by the ecu negatively
mechnificent,
Jan 24, 8:55am
The relays have four contacts. Two are gold coloured and two are steel generally. Two have the triggering power put into them and when that happens some contacts inside close and the other coloured contacts conduct power to the pump.
The relay only has power to the trigger contacts for about one second when you first turn the key on, then it is turned off again until the motor is actually turning over. That is controlled by the ecu(computer).
The other two contacts, one of them has power supplied to it when the key is on, but there is no power coming out of the second one till the trigger is triggered/applied. Once the trigger power is supplied by the ecu at key on or startup, then the power comes out of the second contact and goes to the fuel pump.
If you find the relay and pull it out, then put power into one set of contacts it will click, those are the trigger contacts. When they are energised and the click has happened, then the other two contacts should be connected and conducting enough power to run a decent sized headlight bulb.
mechnificent,
Jan 24, 8:58am
And as Matt says, the underseat connector is prone to getting hot and buggering up, but I'd imagine you've already been there hotwiring the pump to test it. right!
bigfatmat1,
Jan 24, 9:10am
hate to correct ya hard work there mech there is 1 batt supply one ignition supply the output to fuel pump and the neg which is switched via ecu once crank signal is detected
socram,
Jan 24, 9:46am
Don't hard wire the pump.It may be cheap but as an above poster has pointed out, not only will the fuel supply not cut off automatically, in a crash, but it won't cut off in a crash even if the engine is smashed to bits, and could still be pumping fuel onto hot metal.I have witnessed a crash where the BADLY damaged battery was still powering the electrics!
mechnificent,
Jan 31, 12:04pm
Err actualy Matt, in some of the turbo cars there is a timer in the ecu and the relay is fed from the ecu, then to earth. The ecu keeps feeding power to the relay after the ecu is turned off, only for a few seconds though. I'm not sure why because it's not long enough for turbo cooling but. it does.
My post was mainly about testing the relay off the car anyway.
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