Rb25 ecu loosing power

[DropTopRB]

Hey guys, ive got a rb25 into s13 was running a year and a half ago, went to start it 6 months ago and wouldnt start. Found eccs wasnt getting power, jumped the relays and the car started. Now when i jump the relays i get power to the ecu, but when i crank the car over the ecu looses power, light goes out on the ecu and i get a really week or no injector pulse at all. Any ideas????Thanks!

[Kevin.A]

How olds your battery?Does power come right back after you let go of the key?

[DropTopRB]

battery is kinda old, ive had a charger on it the whole time. Its just the ecu loosing the power the rest of the vehicle still has it. Once i stop cranking the engine the light on the ecu does come back on a few seconds after.

[robbie2883]

sounds like somehow either when you tapped your original power or bypassed everything you tapped into a accessory source instead of ignition source. ignition keeps power through start and accessory only has power when the key is in the on position. goes to zero when starting and then back to 12 volts.

[USMCgetsome]

you jumped it wrong! you have it set up to acc pwr instead of 12vdc power. check your jumpers again

[robbie2883]

you jumped it wrong! you have it set up to acc pwr instead of 12vdc power. check your jumpers again

you mean ignition power right?

[DropTopRB]

So i cant jump it from battery power, and run a switch to it???

[robbie2883]

just run it to an ignition wire off the fuse box or even better directly from the ignition harness. i would put a fuse in the wire though