Ignition switch function

[AnWaRi996]

Hey all,

Running a wrxlink6+ and am trying to find the real place for the B136-25 wire. The stock routing is directly into the engine bay and I'm trying to find its home from there. The wire corresponds to DI4 which is the ignition switch however the car still starts without it connected to anything? Not sure what the purpose of the wire is at this point. When putting a voltmeter on it with the ignition on it reads 12v although it is a DI (I thought this meant it fed into the ECU, not out?!). It therefore keeps the car running with the key removed if bridged to other engine bay power supplies, and shorts out the ignition fuse when grounded.

My questions in summary would have to be:
1. What does the ignition switch wire actually do if not lead to starting the car?
2. Where would it go as a result?
3. Is it meant to be a 12v output on a DI channel?

 

TIA

[Confused]

In some ECUs, like my Evo 1-3, it's used to initially power the ECU on, before the ECU Hold Power output takes over and switches the main engine control relay on. Once it goes off, it starts the shut-down hold power timer, to reset idle speed stepper motors, for example, so that it's ready to go for cold start next time you turn the power on.

[Adamw]

It sounds like the wiring has been modified in your car.  With the stock wiring I would expect the ecu could not even power up without B136-25 connected.

Pin B136-25 is connected to both DI4 and another separate circuit which controls the main EFI relay - the relay that supplies 12V to all engine related stuff including the ecu, the role of this input is several;

1. When the ignition switch sends 12V into B136-25 a small passive circuit onboard sends 12V back out of pin B136-32 (which is the trigger for the main efi relay), the Main relay then engages and that provides 12V to the ECU (B136-8 & 9), Injectors, coils etc.  The 12V on DI4 tells the ecu to enable fuel and spark, the engine can then be started.
2. When you switch off the ignition, DI4/B136-25 should drop to 0V and this tells the ecu to stop the engine (cut fuel and spark), but power is not shut off yet - Ignition drive 6 is also connected to the main relay pin (ecu hold power B136-32) so it will keep the engine and all accessories still powered up so it can perform the stepper motor reset in preparation for the next start up.  After a few seconds ignition 6 switches off the main relay so the ecu, injectors coils etc all power down. 

So if your car powers up and runs without 12V supplied to pin B136-25 then that main relay must be getting switched on some other way.  Possibly a back feed from a poorly wired security system or something along those lines.  It also means potentially important functions such as the stepper reset wont be working.

[AnWaRi996]

38 minutes ago, Adamw said:

It sounds like the wiring has been modified in your car.  With the stock wiring I would expect the ecu could not even power up without B136-25 connected.

Pin B136-25 is connected to both DI4 and another separate circuit which controls the main EFI relay - the relay that supplies 12V to all engine related stuff including the ecu, the role of this input is several;

1. When the ignition switch sends 12V into B136-25 a small passive circuit onboard sends 12V back out of pin B136-32 (which is the trigger for the main efi relay), the Main relay then engages and that provides 12V to the ECU (B136-8 & 9), Injectors, coils etc.  The 12V on DI4 tells the ecu to enable fuel and spark, the engine can then be started.
2. When you switch off the ignition, DI4/B136-25 should drop to 0V and this tells the ecu to stop the engine (cut fuel and spark), but power is not shut off yet - Ignition drive 6 is also connected to the main relay pin (ecu hold power B136-32) so it will keep the engine and all accessories still powered up so it can perform the stepper motor reset in preparation for the next start up.  After a few seconds ignition 6 switches off the main relay so the ecu, injectors coils etc all power down. 

So if your car powers up and runs without 12V supplied to pin B136-25 then that main relay must be getting switched on some other way.  Possibly a back feed from a poorly wired security system or something along those lines.  It also means potentially important functions such as the stepper reset wont be working.

Extremely useful, thank you. So this means there's likely an issue in the wiring for B136-32 somewhere where it's getting 12v when it definitely shouldn't? And as for the place for the B136-25, given the wiring runs into the engine bay I should be looking for an ignition switched power source in the bay? My understanding is that I should route it directly into the ignition switch to prevent any issues, but there must be a reason it goes to the bay from factory and a solution there would make my life that much easier.

[Adamw]

B136-25 comes from fuse 11 in the "FB" fuse box, I assume that may be in the engine bay somewhere.  It is hard to find correct wiring diagrams for the V5/6, but for all the engine stuff you can go to the G1 section of this forum, at the top of that forum there is a pinned topic "G1 manuals".  look for the PossumV5.pdf manual, that has the factory engine wiring diagrams in the back pages.  

I think I would start by unplugging the ecu and check if B136-25 switches on/off with ignition then.  Also check B136-8&9 should not switch on with ignition when ecu is unplugged.  I havent thought all the scenarios though well but I guess potentially if there was something damaged on the ecu it could it also cause some odd behavior - so these tests with ecu unplugged will confirm that.

[AnWaRi996]

I've checked the ECU pins and it switches 12v without the ECU plugged in.

From looking at the Possum manual, it appears that the wire actually branches out into various places. It is meant to be connected to the fuel pump relay (there's continuity there), that fuse (FB-11) (which is in the cabin, but there's already continuity and I'm assuming the wire has a path through the dash), and to the 12v of the wasted spark ignition system, on the engine bay side of the wiring.

This leads me to believe that the wire should just be the 12v to the coil from factory. As far as touching other wires, it appears to be touching the purge control solenoid ignition output (B135-7) on its way through the cabin to the ECU at some point, however the purge system is not in use and I believe that's just an unused output at this point and shouldn't affect this.

I think in a stupidly foolish moment I bridged my ignition 12v to a different power source (when converting to coil on plug) and completely forgot that this leftover wire was dedicated to ignition power.

Could explain my pissy purple spark too.

 

Does this sound feasible or am I rambling on making only a tiny amount of sense? It just seems like everything is exactly how it should be but my coils were using the wrong power source?

Attached is the wiring I'm following and how I'd imagine it's actually meant to flow.

 

 

 

 

[Adamw]

Yep you have it right in that drawing.  Fuse 11 should supply 12V to the ign coil, fuel pump relay coil and B136-25.

 

17 hours ago, AnWaRi996 said:

I've checked the ECU pins and it switches 12v without the ECU plugged in.

Do you mean pins 8 & 9?