Spyder No power to ECU

[ryan4269]

Where does the 12v+ power supply leads to the ecu start? I am getting no power to my ecu.

Just finished doing exhaust work and went to start it up and it ran for maybe 10 secs then died instantly, at first I thought I fried the ecu but jumping power to the ecu it starts fine..

I was moving the engine bay fusebox around a bit, is that where it gets its power from? Can I get a pointer to which leads are which, quite the mess in there.
Thanks

 

[steve]

It starts at the battery, then across two of the four white wire to the fuse box, then out the 20A MFI fuse on the large Red/Black wire to the MFI relay pin 3. On the 2.4L Spyder it looks like the power to drive the MFI relay coil comes from the ignition circuit (ignition key) not the MFI circuit like the turbo cars. So both need to be good to turn on the ECU.

Once the ECU pulls pin 2 on the MFI relay low the 12v to power the ECU si switched to pin 1 on the relay and from there on the large red wire to pins 12 and 25 on the ECU.

https://www.dsmtuners.com/threads/2g-basic-ecu-mfi-mpi-relay-circuit-function.497188/

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[ryan4269]

It starts at the battery, then across two of the four white wire to the fuse box, then out the 20A MFI fuse on the large Red/Black wire to the MFI relay pin 3. On the 2.4L Spyder it looks like the power to drive the MFI relay coil comes from the ignition circuit (ignition key) not the MFI circuit like the turbo cars. So both need to be good to turn on the ECU.

Once the ECU pulls pin 2 on the MFI relay low the 12v to power the ECU si switched to pin 1 on the relay and from there to pins 12 and 25 on the ECU.

https://www.dsmtuners.com/threads/2g-basic-ecu-mfi-mpi-relay-circuit-function.497188/

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Thanks, currently pin 25 is dead and I’ve jumped power from the black/red wire from the mfi.

My whoopsie was replacing the o2 sensor with a generic one I had around, I guess the pinouts were different and now that power wire is dead??..

Judging by the schematic, my troubled area is between the mfi and the ecu, but what could possibly break that circuit? I notice that my power leads are solid red, and grounds solid black, and a pinout of the 4g63 describes pin 25 as red/black which matches the mfi power lead, so is it possible the ecu is powered from elsewhere?

I’ll do some more digging, thanks Steve.

 

[steve]

You don't have a 4G63 the 2.4L NA wiring is a bit different. The following measurements are without your jumper bypassing the power.

Do you have 12v at Black/Blue wire on pin 4 of the MFI relay when the ignition is switched on?
What voltage is on the Blue/Green wire at pin 2 of the MPI relay with the ignition on?
What voltage do you measure on the Black/White wire to pins 3 and 4 of the other relay in that set (Fuel Pump)?

Because of how the O2's are wired you can cause a bit of damage if you short or miswire them. There is 12v from the MFI circuit to the heaters and both the 5v sensor power and the sensor ground in the bundle. Miswiring the O2 sensor is how most of the ECU sensor ground get blown.

 

[ryan4269]

You don't have a 4G63 the 2.4L NA wiring is a bit different. The following measurements are without your jumper bypassing the power.

Do you have 12v at Black/Blue wire on pin 4 of the MFI relay when the ignition is switched on?
What voltage is on the Blue/Green wire at pin 2 of the MPI relay with the ignition on?
What voltage do you measure on the Black/White wire to pins 3 and 4 of the other relay in that set (Fuel Pump)?

Because of how the O2's are wired you can cause a bit of damage if you short or miswire them. There is 12v from the MFI circuit to the heaters and both the 5v sensor power and the sensor ground in the bundle. Miswiring the O2 sensor is how most of the ECU sensor ground get blown.

I believe the miswire was the 12v lead and ground being swapped, do you know what would theoretically happen, and what would need to be replaced? What do you mean by ECU sensor ground? Is that internal of the ecu or are you talking about the wiring harness circuit?

I’ll check those voltages later today, thanks

 

[steve]

If you look at the FSM for the 2.4L Spyder you'll see that the ECU turns on the heaters for the O2 sensors using pins 54 and 60 just like the Turbo ECU. So that means the ground side of the heater circuit is part of the ECU and the current is limited by the resistance of the heater.

Then looking deeper you'll see the the O2 sensor itself is connected between the ECU's sensor ground and the ECU +5v sensor power (Both internal to the ECU going back to the microprocessor ADC).

The sensor ground and power are shared with all the analog inputs to the ECU. None of these are going to be happy if you put a direct feed from the MFI +12 power to them and try to discharge the battery that way. It's a race to see if circuit traces inside the ECU or the MFI fuse are going to melt first.

If you don't have said FSM you should download them ASAP from the resources on the site. https://www.dsmtuners.com/threads/2g-1997-1999-dsm-electrical-factory-service-manual.517369/