ECU power, constant vs Switched

[mitsugst97]

Hey guys anyone know what pins are constant and which ones are swithced(ignition) i tested 12,13,25 those should be power but none of them show 12v at anytime, i checked fuses but did not find any blown ones.

They were working but i was trouble shoting my starter and then they stoped, so now my SAFC doesnt come on and my FP doesn't run, i know my SAFC is good because it will come on if i give it 12v.


any ideas would be appreciated.

 

[donmagicjuan]

What did you do to troubleshoot your starter? Usually the best plan of attack for that is to take it off and have an auto parts store throw it on their machine for free.

 

[mitsugst97]

turns out that the starter problem wasn't a problem at all, just missed the Damn little plug that completes the circuit.. felt really dumb after we found it,, but hey i didn't take it out or put it back in so how was i to know...
but my new problem came after i was messing with the relay looking thing on the passenger side of the center column, right under the starter relay.

 

[donmagicjuan]

I might be completely crazy, but I thought the starter relay was in the engine compartment. Are you talking about something on the inside of the car?

 

[steve]

Sounds like the MPI relay, it's what switches the power for the ECU and the rest of the MPI circuit.

IIRC, 12 and 15 are the switched 12v. 13 and 16 the ground. 80 is the unswitched backup power.

Steve

 

[mitsugst97]

so the mpi is what turns the ecu on? it acts like the switch,,, damn then mine might have went bad.

 

[steve]

Relays are pretty robust. Have you checked the MPI fuse and measured that you have power to to the MPI relay?

Steve

 

[f2tzoomzoom]

i'm dealing with this same sorta issue.

no start, turned into checking coil/power transistor....both good (new coil)... CAS was checked, but not 12v or even 5 v......... so theres no way to tell if cas is bad ### theres no power.

so now i'm looking at the ECU and/or MPI relay.......

i'm trying to pin out the MPI relay, and i get 12v constant, a couple grounds, and one switched power, now theres no 5v anywhere (as i understand the ECU runs off of 5v and not 12v). also, 3 wires aren't reading ground or power. 2 though are reading identical resistances to ground, which leads me to believe they're going to the ECU.


does the MPI relay convert 12v to 5v?

and lastly, advanced has no idea what relay i'm holding when i bring it in to them..... this is a bear of a problem

MPI fuse..... under hood, off positive batt. terminal right?

 

[steve]

There is a difference between 1Gs and 2Gs in this area so f2tzoomzoom I suggest to search my old posts for details and then start your own thread. The MPI is just a relay and the ECU gets 12v as input not 5v.

Steve

 

[mitsugst97]

Ok update,
so i found that the ecu is getting switched power from the key, but the blue/light green that goes to the MFI relay pack isn't switching to ground, so it wont energize the MFI relay and the MFI relay cant send power back to the ECu or fuel pump, if i put that wire to ground everything kicks on like it should.
Car still wont fire, but i think i might have cooked my ecu. or atleast part of it.

I have a used one on the way so i will find out soon.