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1G MPI relay question

peon_slayer

Proven Member
230
19
Oct 6, 2008
grande prairie, AB_Canada
Hey guys I am curious about a 1991 talon TSI mpi relay, is pin 8 on the relay supposed to be ignition power or grounded? I have looked on the forum and seen people saying both answers I talked to a good buddy of mine who knows electrical a bit better then I do and he says ignition power but I'd like to be sure before I go and wire it that way. Reason I am asking is my car has a plug and play aem ecu and my MPI relay is not doing anything o i have no spark or anything associated with it. When I go back to a stock ecu the car runs just fine but rich as the car has large injectors which is why I'm trying to put a standalone in it. Please do not turn this into get dsmlink I have a better ecu but it requires me to completely build a harness from scratch and all I want to do is get the car running ATM thanks guys.
 

dustyboner

DSM Wiseman
1,944
1,062
Mar 13, 2016
abq, New_Mexico
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dustyboner

DSM Wiseman
1,944
1,062
Mar 13, 2016
abq, New_Mexico
it looks like pin 10 provides +voltage to one side of the activation coil, pin 8 is the ground side. mpi pin 8 > ECU pin 63 .
the ecu will ground pin 63 to activate the mpi side of the relay.

im not sure about the fuel pump side, the diagrams shows 2 activation coils for 1 switch. 1st time i've ever seen that shit. Good thing you didn't ask about it.
 

steve

DSM Wiseman
14,714
1,586
Feb 3, 2002
Boulder, Colorado
There are two coils on the Fuel Pump side. The starter controls one and the ECU the other. Either can cause the relay to activate.

From my thread in the Technical Articles https://www.dsmtuners.com/threads/1g-basic-ecu-mpi-circuit-function.435961/

"When pin 110 goes high the ECU pulls pin 63 (MPI relay pin 8) low (to ground). This causes the the relay to activate and switches the MPI power from MPI pin 10 to MPI pins 4 and 5 providing power to the ECU on pins 102 and 107 along with various sensors, solenoids, injectors, ISC, and O2 Heater in the engine bay."

The AEM should be doing something much the same, pulling pin 8 to ground to turn on the power to all that stuff.
If your measuring voltages your going to see battery voltage @ pin 8 until the ECU pulls it to ground.
 

dustyboner

DSM Wiseman
1,944
1,062
Mar 13, 2016
abq, New_Mexico
not at all, i learn alot from you :thumb:
 

peon_slayer

Proven Member
230
19
Oct 6, 2008
grande prairie, AB_Canada
I hope I'm not coming across as arrogant as that. It's not intended.
not at all man you are helping out quite a bit I am not sure why that didn't make sense to me reading it on my own but you have been a huge help both here and in PM I hope others can also find this information useful I will update this thread around sept 12th with how I make out! either the aem will finally work or I tear out the stock harness and start building my harness for my big boy ecu that I have had sitting for about a year now just was not quite ready to pull the trigger on that if I didn't need to.
 

steve

DSM Wiseman
14,714
1,586
Feb 3, 2002
Boulder, Colorado
From what little I've read lately about the AEM Series 1 PnP ECU you should be able with their wizard to configure the normal behaviour for the MPI relay. Given that AEM no longer supports or repairs the Series 1 ECU's I'd think long and hard about using it.
 

peon_slayer

Proven Member
230
19
Oct 6, 2008
grande prairie, AB_Canada
From what little I've read lately about the AEM Series 1 PnP ECU you should be able with their wizard to configure the normal behaviour for the MPI relay. Given that AEM no longer supports or repairs the Series 1 ECU's I'd think long and hard about using it.
I'm already hunting for a 1g ecu with link, I'm over this thing
 
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