Fuel pump relay - getting 12v but not energising.

[Boris2k]

So I have some kind of gremlin in my electrical system, made even harder to find since the car intermittently decides to work.

I've narrowed it down to the fuel pump relay not energising even though it's getting 12v (for 3 seconds when ign switched to on) replacement relay won't energise either, though both will energise if i feed them from a battery.

Car runs fine if I bypass the relay and just short the pump to on.

Any ideas what may be reducing the current going to the relay? Intermittently at that? I've checked all the other relays in the car, all seem to work fine, I can't find any blown or damaged looking fuses and none of the relevant contacts are corroded.

Any help would be greatly appreciated.

'95 K11

Edit: also what are the risks of bypassing the relay to enable the fuel pump since it doesn't get 12v until the ignition is on anyway.

 

[frank]

i think the ecu signals the fuelpump earth ?, a safety feature that shuts the pump down if there is no crank signal

 

[Boris2k]

i think the ecu signals the fuelpump earth ?, a safety feature that shuts the pump down if there is no crank signal

so is there something I should check in particular or is the ecu dieing? I have already replaced the crank angle sensor in the dizzy and the car has run fine with it so that shouldn't be a problem.

also, I tried to run it with the relay bypass, engine died as soon as I touched the throttle and the pump is now only being fed 2.5v

 

[frank]

so is there something I should check in particular or is the ecu dieing? I have already replaced the crank angle sensor in the dizzy and the car has run fine with it so that shouldn't be a problem.

also, I tried to run it with the relay bypass, engine died as soon as I touched the throttle and the pump is now only being fed 2.5v

i think you would need to meter the pump pinout on the ecu, the 3 sec priming is working ok eh