1G MPI relay not getting ground from pin 63 on the ECU!

[pikul21gsx]

hi, according to this thread http://www.dsmtuners.com/forums/articles-tuning-ecu/435961-1g-basic-ecu-mpi-circuit-function.html pin 63 from the ECU grounds pin 8 of the mpi relay so that pin 4 and 5 get power and send it to the ecu pin 102 and 107 to get the check engine light and finally start the car.

The problem im having is that ECU pin 63 is not grounding the mpi relay pin 8. i dont know why, what i did to partially fixed it was get a ground from the chassis to pin 8, that way ecu gets power and i can start the car normally.

So my question is, what could be causing this?

This is the second ECU that i put on my car and usually they worked maybe a month or two and then stopped working, yesterday i had time so started looking for info and found the problem that i describe at the top of my thread.

i really need help guys, i had the car running maybe 1 hour fine, later in the afternoon i started it again and now seems like injector number 3 its not working.

 

[wrencher]

Need to OHM out the field coil in the MPI relay on that side. There are 2 field coils on for the pump other for the ECU ,injector,coil power etc.
If the resistance for the field coil is too low it can burn the "drivers" out of the ECU that grounds the field coil from excessive amperage.

Actually the ECU supplies 2 separate ground drivers for the MPI relay on that circuit. They are spliced together in the harness to share the load of the relay's field coil. 63 & 66 both black/w a blue tracer.


ON the MPI relay;
terminal 3 & 7 are the main fuel pump field coil. (3 is internally spliced with supply power for the fuel pump from the ignition switch)
8 & 10 are the ECU's power field coil in the MPI relay.( 10 is internally spliced inside the MPI relay to the main power supply of the MPI fuse on the battery)
Also inside the MPI relay in that coil there is a diode to bleed excess current off of the ECU's drivers.
Need to ohm out & test the diode.
That means polarity of the ohm meter to MPI relay terminals is an important test.
With the negative lead on terminal 8 & the positive test lead on # 10 the resistance should be 250 ohm or so.
I cannot remember the spec of the top of my head
With the tester leads reversed from the above resistance should be very high. over a thousand ohms at least.
I am going off of memory here it has been a while. I dont really have the access to the service info on hand @ home.
If I can remember I find the specs on it....

If this is the 2nd ECU with the same failure something is burning the drivers up.
MPI relay pinouts;

 

[yokotabrat]

Testing the MPI relay coil as wrencher suggested is a good idea.

It's also possible that you've just gotten 2 bad ecus. If these ecus have original caps, check for leakage around the caps. Pin 63 not being grounded by the ecu is a very common failure when the caps leak.

 

[pikul21gsx]

Need to OHM out the field coil in the MPI relay on that side. There are 2 field coils on for the pump other for the ECU ,injector,coil power etc.
If the resistance for the field coil is too low it can burn the "drivers" out of the ECU that grounds the field coil from excessive amperage.

Actually the ECU supplies 2 separate ground drivers for the MPI relay on that circuit. They are spliced together in the harness to share the load of the relay's field coil. 63 & 66 both black/w a blue tracer.


ON the MPI relay;
terminal 3 & 7 are the main fuel pump field coil. (3 is internally spliced with supply power for the fuel pump from the ignition switch)
8 & 10 are the ECU's power field coil in the MPI relay.( 10 is internally spliced inside the MPI relay to the main power supply of the MPI fuse on the battery)
Also inside the MPI relay in that coil there is a diode to bleed excess current off of the ECU's drivers.
Need to ohm out & test the diode.
That means polarity of the ohm meter to MPI relay terminals is an important test.
With the negative lead on terminal 8 & the positive test lead on # 10 the resistance should be 250 ohm or so.
I cannot remember the spec of the top of my head
With the tester leads reversed from the above resistance should be very high. over a thousand ohms at least.
I am going off of memory here it has been a while. I dont really have the access to the service info on hand @ home.
If I can remember I find the specs on it....

If this is the 2nd ECU with the same failure something is burning the drivers up.
MPI relay pinouts;

If you could get me the values it would be great ill try to test it

Testing the MPI relay coil as wrencher suggested is a good idea.

It's also possible that you've just gotten 2 bad ecus. If these ecus have original caps, check for leakage around the caps. Pin 63 not being grounded by the ecu is a very common failure when the caps leak.

The first one was great without leaks at all, just in case i changed the caps anyway, the second one i didnt check, i was so happy i was gonna start using my dsm again thay i didnt think about it