KaLo_o
10+ Year Contributor
- 231
- 0
- Mar 9, 2009
-
Quebec,
QC_Canada
quick question about the MPI relay.....what does MPI stand for and will it prevent the ECU from booting if it goes bad? thank you!
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Actually, the MPI relay is controlled by the ECU, not the other way around.
The way it works is the key turns on and sends a 12v source to the ecu and the MPI relay, at this point you should have a check engine light illuminated. If its not your ECU is bad most likely. Once everything checks out the ECU will send a signal to the MPI relay to switch on.
This is as per the wiring diagram from the 92 talon dealership manual.
So in a sense the ECU turns on the MPI relay which in turn sends a singal back to the ECU thus completely "waking up" the ECU. But the thing to remember is that the ECU is first in line and does turn on the MPI relay.Make sure you have 12v at the MPI fuse on the positive battery terminal?
Then check to make sure you get 12v at pin 103 on the ECU. It comes from the room fuse #19 next to drivers left foot.
The ECU expects to get 12v at pin 110 from the ignition switch when you turn it to run. In response it will pull ECU pin 63 and 66 low to turn on the MPI relay. The MPI relay then applies 12v to ECU pins 102 and 107 and the ECU if it's working correctly will boot up, turn the CEL on while the rest of the dash lights go through bulb check and then turn the CEL off.
If you don't have 12v at pin 10 of the MPI relay the ECU will not power up. If you don't have 12v on pin 103 for backup power the settings for long term variables like fuel trims will reset each time you turn the car off.