1994 Eagle Summit 5v signal and sensor ground showing 12v

[dsmkid303]

Long time viewer first time poster. I'm extremely frustrated and stumped for the first time so I'm posting here in hopes someone smarter then me can explain what's going.

I'll try and make this fast I'm finishing up the wiring on a 1994 Eagle Summit 2g swapped finally got everything together and then noticed in ECMLink I was only getting 2.7 volts at WOT. I checked 5v sensor power and found it wasn't getting full 5v power. Finally traced it down to the ISC I had accidentally wired the power to 5v source instead of 12v fixed that and now have full 5v.

However while i was testing everything I noticed something odd. Unplugged ECU key on so MPI is powered and grounded on harness hooked up to everything else I was seeing 12v on the 5v sensor power and the ECU sensor ground, unhook MAF and it goes away? With ECU plugged in I get 5v and sensor grounds like normal MAF functions like normal along with everything else am I overthinking this?

I have pretty much tested continuity over every inch of the harness and checked for multiple shorts to power with no luck but I'm only seeing it with key on MPI on ECU unplugged MAF plugged in. Not trying to burn up sensor grounds or 5v reference circuits in the ECU.

 

[habitatguy187]

Pretty sure it’s supposed to be 12v when the ECU is unplugged because that’s the same thing that happens when the ECU ground blows.

Maybe wait until someone more knowledgeable chimes in.

 

[steve]

It's getting late and I'm still groggy from a 14 hour banzai run from Boulder to Chicago yesterday but I can't figure out what you are describing?

Without the ECU plugged in you shouldn't have anything on the the Sensor Power wires since the ECU sources that. Also with the ECU disconnected the MPI can't activate so only those things powered from the ignition switch would see 12v.

 

[dsmkid303]

Pretty sure it’s supposed to be 12v when the ecu is unplugged because that’s the same thing that happens when the ecu ground blows.

Maybe wait until someone more knowledgeable chimes in.

That would make sense on the sensor ground side if that's the case maybe it's possible the MAF is causing it to back feed through the 5v sensor power aswell would make sense why it goes away when MAF is unplugged?

 

[dsmkid303]

It's getting late and I'm still groggy from a 14 hour banzai run from Boulder to Chicago yesterday but I can't figure out what you are describing?

Without the ECU plugged in you shouldn't have anything on the the Sensor Power wires since the ECU sources that. Also with the ECU disconnected the MPI can't activate so only those things powered from the ignition switch would see 12v.

MPI turns on when grounded and ignition switched on, at least on the Summit, then it feeds 12v to the sensors and ECU on pins 12 and 25.

The 2g is ECU controlled on the MPI and the fuel side. Maybe that's why I'm getting these odd reading. I thought the same shouldn't be seeing anything on the 5v circuit with ECU unplugged yet I'm getting 12v I can't find anywhere on the harness that has continuity with a 12v source either but when MAF gets unplugged it goes away.

I've put in a few different MAFs and connectors on it does the same thing with all of them. ECU plugged in it seems to function like normal as well.