ECU not getting power

[Red Civic LS-T]

I have a 92 Civic CX hatch with a JDM B18B, a T3/T4 turbo, and a P28 ECU tuned on crome.

Problem: When key is turned to ON, the ECU doesn't get power from the battery or main relay. Therefore the fuel pump doesn't kick on, and the CEL stays on solid regardless of whether the service connector is jumped or not (no blinks, Code 0).

Things I've already tried:
- Changed out main relay
- Subsituted ECU for a known good ECU
- Replaced my hacked CX engine harness with a DX harness
- Checked for voltage at fuel pump (no voltage)
- Jumped the fuel pump connector at the main relay (fuel pump kicks on but ECU still not getting power)
- Checked for battery voltage at A25 ECU pin (no voltage)

So basically, I know it's not my engine harness, main relay, ECU, or fuel pump causing the problem. What else could it be???

 

[Red Civic LS-T]

Anyone?

 

[MoSeS]

sounds like you have a bad connection to me but thats just my guess... if you did a voltage test and you weren't getting any power then you just need to find out where you are losing power at.

 

[Red Civic LS-T]

I jumped the fuel pump at the main relay connector and it kicked on. So this means that I'm getting voltage at the main relay but there is a bad connection somewhere between the relay and the ECU? Is this correct, or am I way off?

My understanding is that the battery voltage goes through the main relay before it gets to pin A25 of the ECU (where I currently have no voltage).

 

[CIV98DX]

I don't know if this would be like the problem I just had with my 1998 Civic. Ended up having a wire that wasn't ground....we found this out after we had already replaced the battery, alternator, speed sensor and one O2 Sensor. I'd check and make sure all your wires are okay.

When we called Honda we were checking on a price for the ELD (Electrical Load Detector); told the guy my problem and he suggested checking the wires to make sure there wasn't a loose connection and...that turned out to be the actual problem which probably meant we didn't need to replace all the parts. Hope this helped!

 

[handlebarsfsr]

check the ground on the thermostat, and then from the tranny and valve cover to the chassis. also, check your fuses.

 

[CIV98DX]

???

are you telling me to do that?

we already fixed the problem. thanks though.

 

[Red Civic LS-T]

I disconnected, wire brushed, and reconnected all of my grounds. All of my fuses are fine.

At the ECU, pin A25 doesn't show battery voltage with the key on, but D1 (backup power) shows battery voltage all the time. At the main relay, the yellow/white wire shows battery voltage all the time, even when the relay is unplugged. The yellow/black wire doesn't show any voltage with the key on or off. Is this correct for normal operation of the relay?

 

[Red Civic LS-T]

Problem Solved!!!

Ok, I finally figured it out! I was trying so hard to figure out how a good relay could have 12V coming into it but nothing coming out of it. Then I realized that it also needs a 12V signal from the ignition. As a test, I jumped a 12V signal to the ignition wire going into the relay and the fuel pump kicked on! Woot woot!!! So all I need is a new ignition cylinder and the turbo hatch is back baby!