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all black 4G63

Proven Member
254
43
Aug 5, 2019
Chicago, Illinois
Would like to know if it will cause any damage to the ECU if the MPI relay is eliminated and switched B+ is ran to pin 107 (C-59) of the ECM?

I would also be eliminating all factory fuel pump control circuits (pins 56, 13, and 108 at the ECM) as I would run a HP pump on a separate replay and switch?

I am assuming pin 108 (C-59) is used as a crank sense to enable fuel pump control after the key is rotated from start to run and an RPM signal is obtained? I assuming the ECM does this by applying ground to pin 56 (C-60) after the key is rotated from "start" to "run"?

I am also assuming the ECM applies ground to pin 63 (C-60) to close the MPI relay contacts when IGN B+ is applied to pin 110 (C-59) when the key is switch to KOEO?

I have attached a photo of the MPI Circuit out of the 1992 Laser/Talon Electrical service manual. I am working with a 1992 TSI manual AWD

Thank you for your input and assistance.
 

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If you are using a stock ECU you need to retain the power side of the MPI relay as the ECU needs to control the power down in order to be able to modify/save any tunes/changes. If you are using an aftermarket ecu, it shouldnt matter.

The fuel pump control can be run on a standalone switch if you wanted, but if you were running a stock ECU I would just allow the ecu to control it.
 
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You can think of a relay as being just like the light switches in your house, but with one big difference: Instead of turning on the light by a little lever or button, in a relay you turn it on by sending it a small amount of electricity Tutuapp 9Apps Showbox.
 
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