Resolved 1G MPI Relay won't turn off

[90gsxftw]

Have read every thread on MPI relay and nothing has helped. I'm not having the problem of no start but rather the problem of a dying battery because of the MPI relay. It won't shut off and is causing a parasitic drain to my car. I have verified this with multimeter and plugged MPI relay in with case off. As soon as I plug it in it clicks and closes the connection.

From what I read the ECU is not grounding the MPI relay there for de-energizing it and turning it off. Have checked all grounds that I could find with multimeter and there good ECU has been rebuilt and caps replaced by Jeff. Now as for grounds does anyone know where the ECU grounds are on 90 GSX? Or have I missed anything? And MPI relay hums if I plug it in then plug ECU in.

Any help cause I'm having to pull the relay every time I get out of my car. Also checked all fuses. Will be getting a spare ECU to check next week but I am out of ideas.

 

[steve]

Does it do this when the ECU is unplugged?

You have the way it works backwards, the ECU switches to ground the wire from the relay coil when it wants to activate the relay and lets it float the rest of the time. When the one side of the relay coil is grounded current flows and causes the relay contacts to close switching power from the MPI fuse to the ECU and the rest of the MPI circuit under the hood.

If the MPI relay still turns on with the ECU removed you have a short in the wiring or something else pulling the wire between ECU pins 63 and 66 and the MPI relay to ground.

If it doesn't there is a problem with the ECU or the signal from the ignition switch telling the ECU that the relay should be on.

Do you have a multimeter and know how to use it?

 

[90gsxftw]

No the relay lets go as soon as I unplug the ECU, and yes I have a multimeter and know how to us it.

Hopefully the ECU I get soon will solve things I'm not ruling the ECU out just yet till I get this other one and if it is the ECU I'll just have to send it to ECMtuning to get it fixed.

 

[steve]

Good, check pin 110 at the ECU and see if it's grounded (0v) when the ignition is off and at battery voltage when the ignition switch is on.

With the ECU unplugged measure the resistance between pin 101 and pin 63. I'll verify a good one here but it's shouldn't be a short.

 

[90gsxftw]

Okay will do, what will this tell me, if there is a short or if my ecu ground
is maybe rusted or corroded.

 

[steve]

It will tell you if something is telling the ECU that the ignition switch is on all the time or if the IC used to switch the MPI relay is blown shorted to ground.

You don't say but I'm assuming the car runs but the MPI relay won't shut off so the battery runs down. The car running would suggest that the ECU grounds are just fine but that there is a problem in the circuit controlling the MPI relay.

 

[Mr PopUps]

Could be the caps, they run right through the MPI circuit IIRC.

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[steve]

Could be the caps, they run right through the MPI circuit IIRC.

ecu has been rebuilt and caps replaced by Jeff.

Your memory is fine but you're grasping at straws. While the capacitors can damage IC110 (which controls the activation of the MPI relay) and other parts of the ECU. They don't typically cause this problem. Rather than jumping to conclusions based on limited data or completely discounting the provided data, I'm trying to diagnose the root cause of problem based on how the MPI circuit works.

The odds highly favor the ECU being damaged but some simple testing will help confirm.


90gsxftw, if you want to take pictures of your ECU that won't hurt.

 

[Mr PopUps]

Your memory is fine but you're grasping at straws. While the capacitors can damage IC110 (which controls the activation of the MPI relay) and other parts of the ECU. They don't typically cause this problem. Rather than jumping to conclusions based on limited data or completely discounting the provided data, I'm trying to diagnose the root cause of problem based on how the MPI circuit works.

The odds highly favor the ECU being damaged but some simple testing will help confirm.


90gsxftw, if you want to take pictures of your ECU that won't hurt.

Sorry missed the part in the rambling about it having them replaced already.

Im not grasping at straws, ive seen leakage cause the cruise control to not disengage and almost caused the person to wreck. I will say this is the first one ive heard of where the relay wouldnt shut off.

When did this start happening? Is the MPI fuse shorted out somehow?

Another option is that if the FP is rewired, that it was done incorrectly and it maybe backfeeding to the MPI relay keeping it on? Thats a far stretch though knowing how a relay is normally hooked up, if anything it would isolate the MPI relay even more.

 

[90gsxftw]

I looked at the ECU super close and two traces are scratched pretty bad, in between the capacitors, I think this is my problem. The new ECU is coming in 2-3 days. The whole problem started when I switched ECU's, so I ruled out ignition or fuel pump rewire, maybe they got scratched when replacing the caps.

 

[90gsxftw]

Just found out ongreenperformance ripped me off, the ECU is a 91-94 I should have seen it cause I was getting fuel trims outside of 60 to 120. They sold it to me saying it was only ment for 90 models car only. I am running this ECU with a MAFT setup cause if I try and run it with a 2g MAS the car jerks past 5psi or 4k rpms. The ECU was chipped for 2g MAS and Evo 9 injectors but this ECU looks like a 91-94 ECU and has the fuel trims to prove it. I'm sending it back right away and demanding a refund.

 

[steve]

So you bought a "new" 90 ECU from ongreenperformance and they sent you a 91+ ECU?
Unless they included the tach adapter board to make the later ECU work in a 90 you should send it back.

Did you try it in your car? If so did it fix the issue with the MPI relay?

 

[90gsxftw]

The ECU was chipped by Jeff O and it didn't show signs of having a tach adapter board. It ran the car for a while but was impossible to run with a 2g MAS. The only way it would run it with a MAFT setup.

I just got my original ECU back from ECMTuning fully repaired and as soon as I plugged it in the relay let go and car ran fantastic. Hopefully they give my money back or we'll have a problem.

 

[steve]

Did Tom and Dave tell you what they fixed?

 

[90gsxftw]

my original ecu practical blew up so they had to replace the top half and the middle portion of the board works perfect now.