91 awd turbo, mpi relay question

[dsm dominator]

so i have found the lil bastatrd that is draining my battery, its my MPI relay, is it possible just to hook the power wire (pin 8 or sumthing) to a switch so i can just cut the power whenever i turn off my car?


also how can i tell if its the relay itself that is the problem,(ie short, or bad relay) of if it is infact a bad ecu?

o and i have searched the forums, i could get as far as pinpointing were the drain is

 

[steve]

The MPI relay is really two relays in on can. One serves to turn on the power to the ECU, MAF, CAS, Solenoids, ISC, Injectors, etc. The other is to power the Fuel Pump and it has two inputs. The ignition switch START position and the ECU.
It far easier to swap the MPI relay and it would be to emulate what it is suposed to do.
How did you decide it was the problem?

Steve

 

[dsm dominator]

well to find the drain i first searched the forum for the clicking that that little gold box was making.

then i found out that it was my mpi relay,
so i took my multi merter and started testing



the first thing i tested was the connecter for the fuses directly off my battery,
then i tested different pins off of my mpi connecter (female side) and one of the pins (first on the bottom of the connecter) read the same volts of when i tested off the battery...I forget the exact volts i think it was 7.6...

so i kept reading the forums and learned to test for voltage drops when the key was turned on, and i found 2, the first pin i explained and one (either the second or third i believe) other..so I went to my local parts store and they told me to go to the dealer,and thats were the switch idea came up, i just would rather spend a dollar over a dealer rice for a fix



thanks fot the help!

 

[steve]

I'm not sure but I think that procedure is faulty.

I think pin 10 is the one your talking about first. It's one end of the coil used to turn the MPI Relay on which when plugged to the harness runs to the MPI Fuse. The other end of that coil is pin 8 which the ECU grounds when it wants to turn the Relay on to power up the MPI circuit.
Since power from the MPI Fuse is always on, pin 10 should be at battery voltage and pin 8 will be close to that but no current will flow until pin 8 is grounded.

The manual doesn't seem to give the resistance specs for the coils and I don't have a spare to measure them. What the manual gives for a test procedure out of the car is to apply +12v to pin 10 and ground pin 8 while measuring pins 4 and 5 to see that the relay switches on.

The check the fuel pump side of the relay by measuring continuity between 3 and 2 while applying power to 9 and grounding 6. Again checking to make sure that relay switches.
The checking the other input to that relay by applying power to pin 3 and grounding pin 7 while measuring pin 2 to see that it gets 12v when the relay switches.

For finding what's draining the battery you'll need to sit down with the wiring diagram and start measuring the current being pulled at various parts of the circuits.

If you find that the MPI relay is still bad you can buy parts online at 20-30% discounts over dealer list from several places.

Steve

 

[dsm dominator]

wow, thanks


......thats a kick ass answer, i bow my head to you sir