Pin 13 for 91-94 ECU Harness

[AWD_FIEND]

My ECU fried on me last week and through my research (including an obvious burnt IC) I concluded my ISC motor failed causing a massive short. When I sent my ECU in to see if it could be repaired the tech told me the damage occured in the fuel pump circuit. This has been bothering me because as chance would have it, my fuel pump did stop working which was the original culprit to my car not running. After I replaced the OE pump the car still didnt run which led me to suspect the ECU. I studied the factory wiring diagram and cant understand how if the FP shorted it could make it back to the ECU through the open MFI Relay, and that's what lead me to the mysterious Pin 13. Pin 13 is wired in series to the positive side of the pump, but bypasses the Relay going directly back to the ECU. Does anyone know what Pin 13 is used for, or if it may have shorted my ECU? I cant install my new EPROM without knowing. Thanks.

 

[ilco187]

ecu pinout.

 

[AWD_FIEND]

Thanks for the diagram, but I'm still confused about what Pin 13 actually does. Pin 56 is the trigger wire for the MFI Relay to the FP, and the ignition switch and Pin 110 provide 12+ so what purpose does Pin 13 serve. Is it grounded in the ECU, is it 5v+ supply, or 12v+ supply? Could that wire backfeed and damage the ECU?

 

[AWD_FIEND]

Wait Pin 56 is the trigger wire ground for the MFI Relay, and Ignition Switch/Pin 110 is 12+ for the MFI. Pin 13 must be grounded in the ECU for the purpose of signaling that the FP is running perhaps for diagnostic purposes?

 

[ilco187]

Pin 13 is the sense line for the fuel pump. You'll find it listed in the 1G Tech manual and the actual 1990 FSM but it's missing from the later manuals. Without it the ECU will throw the fuel pump CEL as soon as the ECU turns on it's output on pin 56. Pin 13 connects to pin 2 on the MPI relay (or wherever your power for the fuel pump is being sourced from.

that might be it.

 

[AWD_FIEND]

Might be, but I have to know for sure. I got a socketed EPROM to replace my burnt hunk of shizzle and paid a pretty penny, so I dont want to install it and cook that one too. I'm going to test the harness anyway, but I'd like to narrow down my possibilities so I'm not wasting time testing stuff that's irrelevent. If you know anyone that's very familiar with the ECU sick them on my thread. Thanks.

 

[ilco187]

i would say PM dsm wiseman ''steve'' he know quite alot about this.

View Profile: steve - DSMtuners.com

 

[AWD_FIEND]

Thanks, I'll try that. He knows his stuff, I'm hoping he'll get in on this.

 

[steve]

Does anyone know what Pin 13 is used for, or if it may have shorted my ECU? I cant install my new EPROM without knowing. Thanks.

Pin 13 is simply the feedback to the ECU that the fuel pump was getting 12v. If the ECU turns on the fuel pump relay via pin 56 and doesn't see pin 13 also go high it throws a fault code.

Since I don't have anything to verify what the cause of the damage really was I can't say anything other than I really doubt pin 13 has anything to do with it.

 

[AWD_FIEND]

Pin 13 is simply the feedback to the ECU that the fuel pump was getting 12v. If the ECU turns on the fuel pump relay via pin 56 and doesn't see pin 13 also go high it throws a fault code.

Since I don't have anything to verify what the cause of the damage really was I can't say anything other than I really doubt pin 13 has anything to do with it.

Thanks for the response I really appreciate it. I thought it might be for diagnostic reasons but I wasnt sure. I tested all the wires in the FP circuit and nothing was shorted. My only conclusion is the fuel pump itself seized causing a massive temporary voltage spike. Or maybe the tech is wrong about why the ecu failed...

 

[steve]

Or maybe the tech is wrong about why the ecu failed...

That's very possible since the ECU is isolated from the fuel pump by the MPI relay.
But since you didn't use me to fix it I can't really do more than speculate.

 

[AWD_FIEND]

I was afraid you would remember sorry about that. I couldnt afford the eprom you had so I bought a stock replacement from a local vendor (which turned out to be an eprom by luck), and used my burnt unit as a core. But when he unbolted the board from the case there was a huge hole through it from the short, so I was only able to get partial credit. All in all I was out the door for $120 which was already a stretch.