Expert Electrical Advise Needed

Greetings... Before state the problem, I will, as briefly as I can, fill you guys in on what has been done, what we are doing, and what we can't figure out (why I'm asking you guys).

Truck: 2005 Tacoma

This truck is being built to eventually race as a hobby, time and funds pending. I could go on and on about suspension and where the truck is at in the full build, but that's not why I'm here. We'll be making a write up when we're done.

The truck had a stage 1 setup from URD. After encountering some failed head gaskets, we decided to go ahead and pull the engine and rebuild the whole thing with balanced forged internals, head studs, new water and oil pump, and of course the appropriate bearings and seals. After the build was complete, we decided to go ahead and upgrade to a stage 2 kit. (I do have to say, those Doug Thorley headers and stainless 3" exhaust look sick).... Anyway, we got the motor reinstalled and wired up. After a fluids check and once over, she fired right up. Purred like an angry kitten. After some idle time and diagnostics we shut it down for the day.

Came back 2 days later to continue work on it. All we needed to do was reinstall the front coil overs and wire up the electric fan.... So we got to work. FYI:yes the battery cables were removed prior to any modification to the vehicle after we had it fired up. We reinstalled the coil overs and wired the fan to the battery terminal with an in-line fuse along with an in-cab switch for activation.

We tried to fire the truck up and it turns over, but there's no fire.

Checked they batter terminals and they're nice and tight... Try to start it again, no fire.

So, of course, check fuel and spark.... There's no fuel. Check the fuses. Fuses good. Check the relays. Ended up replacing some of the relays just for a piece of mind sake. (EFI, open circ, fuel pump). Tried to fire again.. No fuel.

Alright, jump the pump to test it. Pump works great.... So it's electrical.

Pulled up a wiring schematic from Mitchell 1. Started testing power in the fuse box.

-40amp efi fuse: good
-power to efi relay: good
-trigger to efi relay: nothing there

Traced that wire to its source, the ecm. Decided to replace the ecm and crossed our fingers that URD's UCON piggy back wasn't damaged... Tried the test again. Fuse and power good, except this time the trigger got power, but only 3volts.

So now we're thinking that there's a short somewhere. Is this a correct diagnosis? Is there something else we forgot to check? It's boggling us how it went from firing to not firing. Electrical experts! Help!

 

Are you sure the URD piggy back ecu isn't acting up? One of our master diag techs has a Tacoma that kept misfiring and it was the piggy back. And make sure the engine ground strap isnt loose or corroded