Resolved 1G ECU bad or MPI relay? No crank no start

[Oilers199099]

Hello
I replaced my ecu and i am not getting a CEL light for 5 seconds. There is a one click when I try to turn the key behind the ecu. What can it be and where should I start. Any help will be grateful

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I sent a spare ecu to ECMTuning this week. My other ecu was sent to foreign auto for repair but when I received it no check engine light at start up.

 

[Oilers199099]

You want me to put the red wire to pin 10 and the black wire to ground and measure it in ohms?

Then pin 8 to same way and so on?

Or pin 10 to red probe to pin 8 black probe?

 

[steve]

You want me to put the red wire to pin 10 and the black wire to ground and measure it in ohms?
Then pin 8 to same way and so on?

No.

Or pin 10 to red probe to pin 8 black probe?

Yes.

I wanted to check if the diode or coil on the MPI side of the relay was open by measuring the resistance between the two pins. Because there is a diode in series, you need to check in both directions because diodes block current flow in one direction and pass it in the other. If it was open would explain why then it's plugged in you see battery voltage voltage @ pin 10 but nothing at pin 8 and mean you need a new relay.

 

[Oilers199099]

No.


Yes.

I wanted to check if the diode or coil on the MPI side of the relay was open by measuring the resistance between the two pins. Because there is a diode in series, you need to check in both directions because diodes block current flow in one direction and pass it in the other. If it was open would explain why then it's plugged in you see battery voltage voltage @ pin 10 but nothing at pin 8 and mean you need a new relay.

With the key in the on position pin 10 red to pin 8 1.1 ohm reading with the key off I get nothing. I added a new relay last week

 

[steve]

Since these tests were to be with the MPI relay disconnected the results are suspect. If you have changed anything other than getting the ECU back in the last week all the prior data points are invalid and need to be checked again. I'll be happy to expand on how the 1G MPI circuit works if there is something in https://www.dsmtuners.com/threads/1g-basic-ecu-mpi-circuit-function.435961/ that isn't clear or to explain what might be going on if things don't follow the description in it.

 

[Oilers199099]

Disconnect the MPI relay and measure the resistance across pins 8 and 10 with the red lead on pin 10. There is a diode in series with the coil here so one direction will have a relatively low resistance and the other direction a very high one.

While your at it measure the resistance of the harness on the Black/blue wire from pin 8 on the MPI to Pins 63 and 66 at the ECU. You should have continuity (close to 0 ohms) between the two.

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I am sorry if I am confusing you. I am learning. I tested the relay and this is the picture. The other tests was on the harness with the relay disconnected.

All the tests I sent was with the relay disconnected. Those values were from the harness. I haven’t done any tests with the relay in.

 

[steve]

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So that says 0.5 Megaohms (The "M' next to the ohm symbol) in that direction which is pretty high resistance pretty much like no connection in that direction. if you swap the two probes what do you get.

Also make sure we are looking at the right pins.

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[Oilers199099]

So that says 0.5 Megaohms (The "M' next to the ohm symbol) in that direction which is pretty high resistance pretty much like no connection in that direction. if you swap the two probes what do you get.

Also make sure we are looking at the right pins.

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Pin 10 red probe to pin 8 this is the reading the other way I get zero

 

[steve]

Good, a reading of zero ohms is great in that direction. The next test would be to apply 12v to pin 10 and ground to pin 8. The relay should click and you should see 12v at pins 4 and 5. (with the black probe connected to the same ground)

 

[Oilers199099]

Ok I appreciate your patience with me. I have 2 relays here. Let me try that next

 

[Oilers199099]

Ok I appreciate your patience with me. I have 2 relays here. Let me try that next

It clicks and I get 12.67 volts on 4 and 5 each

 

[Oilers199099]

Should I ground pin 8 with a back probe when I install the mpi relay in the car so the voltage from pin 10 and pin 8 grounded gets transferred to pin 4 and 5 to send a voltage to pin 102 and 107.

 

[steve]

You can try it. With it plugged in, grounding pin 8 (same as ECU pins 63 and 66) and see if you then see battery voltage at pins 4 and 5 (which should be the same as ECU Pins 102 and 107).

If you get battery voltage then check to see if the CEL turns on for 5 seconds after you ground pin 8.

 

[Oilers199099]

Hi Steve

I am still trying to figure how to ground pin 8 with the relay on. The back side is closed so I can’t back probe. I am trying to slide a wire and close the relay to the harness so one wire sticks out. I’ll update you if I get a light.

 

[Oilers199099]

Is pin 8 black with blue stripe? I seen in one of your other chats. If that’s the case then I can back probe and ground it. Thanks so much for your help again.

 

[steve]

Is pin 8 black with blue stripe?

Yes, Black with a Blue stripe. That's what the BL means next to the lines on the schematic.

 

[Oilers199099]

Omg Steve I got it. The mpi relay is not getting grounded. Not sure maybe bad ignition switch or ground? I got the check engine light on. I got spark and I am going to check fuel next. I appreciate everything you did for me. Can you email [email protected] if I can send you something for your time. Finally I got a answer

 

[steve]

So since is unlikely the ECU from ECMTuning is bad the next steep is figure out what's wrong in the car that isn't causing the relay to trigger.

 

[Oilers199099]

So since is unlikely the ECU from ECMTuning is bad the next steep is figure out what's wrong in the car that isn't causing the relay to trigger.

Yes maybe the ignition switch or a bad ground from here I am not sure

 

[steve]

Multimeter is your best friend.

 

[Oilers199099]

Multimeter is your best friend.

Ok thank you. It’s helped a lot still learning but I have progress

 

[Oilers199099]

Multimeter is your best friend.

Any suggestions on what might be the issue on why I have to ground pin 8 on the mpi relay while I trace some steps with the wiring. I seen the diagram you sent and ig1 is suppose to send a signal pin 110 to ground pin 8 so what do
You think would be all the related issues causing it?
Appreciate all the help.

 

[Vegas Smith]

I'm no wiring guru but the diagram appears to show the ecu giving ground to the mpi. If the ecu is good, check the MPI connector from the ecu. Perhaps the it's old or the pin is weak?

 

[steve]

So did the engine start once you grounded pin 8 in the MPI relay?

In the past people have had issues with the mating pins in the connectors not making good contact or cut from installing aftermarket alarms or turbo timers. Once I reach this point I have to measure and record everything making sure that the wires still connect to the places they should and thee the voltages do what they should for things to work. The problems pop out once you find something that doesn't follow the normal behaviour and investigate why.

 

[Oilers199099]

The engine turns over and I checked it has spark. I am going to check for fuel today. Before I got no spark before grounding pin 8. So I have something less to test for the starting issue.

 

[Oilers199099]

So did the engine start once you grounded pin 8 in the MPI relay?

In the past people have had issues with the mating pins in the connectors not making good contact or cut from installing aftermarket alarms or turbo timers. Once I reach this point I have to measure and record everything making sure that the wires still connect to the places they should and thee the voltages do what they should for things to work. The problems pop out once you find something that doesn't follow the normal behaviour and investigate why.

Thank you so much for all your help. If I didn’t ground the relay I would never been able to figure it out. After that we ran a wire from the s terminal to the ignition and it started up. Appreciate everything means the world to me.

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