[solved] Injector wiring sanity check..

[Tired2]

So, I am running an MS2 on MS3.0 Main board, fuel and spark.

I have had the car running, but I'm at the idle tuning stage. While troubleshooting why my stock ECU has decided not to run the fans anymore, I did not want to run the MS ECU, so I pulled the fuse for it.

I currently have ignition switched 12v going to a fuse box, and I power my fuel pump 12v+, injector 12v +, and spark 12v+, and ECU off separate fuses from that box. (20A fuel, 5A per inj, 10A spark, and 2A ecu).

With the ignition switch on, the 12V line to each injector is always hooked up, and the ground wire is controlled by the ECU, from my recollection by a P-Type transistor. If you pull the ECU fuse, but leave the fuse hooked to the injectors, the gate of the transistor floats, and the ground side of the injectors is grounded, completing the circuit. For my 2.9 ohm low z injectors, that means 50 watts being dissipated in each injector. Luckily I heard them fire and realized they were getting really hot before I melted them... they all still ohm out okay, so hopefully they are fine.

So, on to my questions... Am I correct about what happened when I pulled the fuse to the MS ECU while still allowing power to the injectors?

Did/does the same thing happen with the BIP373 coil drivers?

Assuming so, I know now not to pull JUST the ECU fuse, and to also pull the other fuses (preferably first).

So, assuming I'm not mistaken above... what happens if the ECU fuse actually blows in operation? Flooding the engine is not my concern, I'm worried about toasting lots of low Z injectors because the software peak and hold current limiting only works if the ECU has power.

Last question... should I just go ahead and pick up a resistor box and ditch all the low Z peak and hold stuff?

Thanks.

[racingmini_mtl]

Check the recommended wiring here: http://www.msextra.com/doc/index.html#schems. You should never have anything connected to the MS that is powered when the MS is not powered. Moreover, you should have injectors and coils powered by the fuel pump relay because then they only get power when the MS is ready to control them since the fuel pump relay is activated by the MS (of course this assumes you control both fuel and spark from the MS).

And there is no reason to use a resistor box if everything is correctly wired and set.

Jean

[Tired2]

Thanks for the reply.

Looking at the 'official' external wiring guide, that seems like it would work out better. I'll have to convert over to that from what I have now.

I'm a bit disappointed... I tend to think very highly of Symtechlabs, but if you check out their 420a schematic, I've wired it very close to that, which in the event of a pulled fuse or blown fuse can damage your injectors and coil. I'm not a Symtech ECU customer, so I have no right to complain about their documentation, but I think any users of that style of wiring should beware.

^ EDIT: I was mistaken, they are still excellent at what they do. See next post.

I'll not link it here, but if you search 420A megasquirt on google images it comes up. Unfortunately with MS, there is so much unofficial, and quite a lot of 'official' information out there it can be really hard to get it right the first time.

Thanks again for pointing me in the right direction, I'll fix up the wiring and continue on.

[SymTech Laboratories]

Thanks for the reply.

Looking at the 'official' external wiring guide, that seems like it would work out better. I'll have to convert over to that from what I have now.

I'm a bit disappointed... I tend to think very highly of Symtechlabs, but if you check out their 420a schematic, I've wired it very close to that, which in the event of a pulled fuse or blown fuse can damage your injectors and coil. I'm not a Symtech ECU customer, so I have no right to complain about their documentation, but I think any users of that style of wiring should beware.

I'll not link it here, but if you search 420A megasquirt on google images it comes up. Unfortunately with MS, there is so much unofficial, and quite a lot of 'official' information out there it can be really hard to get it right the first time.

Thanks again for pointing me in the right direction, I'll fix up the wiring and continue on.

We're not quite sure what you're referring to, but none of our wiring diagrams suggest that the injectors or ignition coil should be powered when the ECU is off. We tried to be very clear that these things should be powered by a relay controlled by the MegaSquirt ECU. Our 420A diagram was designed to be minimally invasive when starting with the stock 420A harness, but otherwise it is very similar to the "standard" MS/Extra wiring diagram.

[Tired2]

Thanks for the response...

You are correct, I think I misinterpreted the wiring diagram for the 420A from Symtechlabs.

It does indeed show the injectors, coil, etc being powered off the output of the ASD relay, not from the battery directly.

Thanks for the response, keep up the good work.

[Tired2]

Okay, so I was contented a few hours back, but when trying to discuss my wiring screw up to a friend, I was explaining that if the MS blew its 3A fuse in this diagram: http://www.msextra.com/doc/general/ms2external.html .... And the ignition switch was on, wouldn't the fuel pump P-Type relay driver lose the pull up voltage on its gate and allow a path to ground for the fuel pump relay, similar to what I had happen with my injector in the original post?

I think I'm losing my mind, but in effect if the ECU loses power while the hot side of the fuel pump relay is powered, is seems like the circuit would complete, powering the injectors and coil anyway, which I'm trying to avoid.

Before I rip up my wiring to fix my initial screw up, I want to get this clarified. If the fuel pump driver was N-Type, providing the 12v+ to the fuel pump relay, everything would make sense, but I'm having trouble seeing how wiring through the fuel pump relay really helps in the event the 3A fuse blows.

Thanks for sticking with me on this, I feel like I'm wrong and I'm just missing some detail.

[slow_hemi6]

The relay driving transistors are a NPN type. No base to emitter current means no collector to emitter conduction. That means the relay coil does not get grounded. Relay coils have 12v supplied and MS ground switches the coil when the uP pin goes high and drives the NPN's base.
Here is how to keep from having problems. http://www.msextra.com/doc/general/ms2external.html

[Mustangous]

Im sorry to jump into your thread, but now you got me concerned, slightly. In reality I don't think my key will be on much if my ms happens to blows a fuse. I would obviously know something is wrong (car wont start) and fix it. Having said that, I have a ms3x and just got done wiring it almost as the op. Just like this --> http://www.diyautotune.com/images/mshar ... wiring.png
Only difference is that the fuel pump relay is seperate other than the ground (pin 37) from ms3x.

Would i have anything to worry about?

[SymTech Laboratories]

Though we prefer to have the MegaSquirt ECU control power to the injectors and coil through the fuel pump relay output, that's also an appropriate way to wire it. Everything is controlled by the ignition switch, so the injectors and ignition coil can't be powered independent of the ECU.

[Tired2]

Though we prefer to have the MegaSquirt ECU control power to the injectors and coil through the fuel pump relay output, that's also an appropriate way to wire it. Everything is controlled by the ignition switch, so the injectors and ignition coil can't be powered independent of the ECU.

Assuming you are referring to the DIY auto tune diagram, if the 3A fuse is pulled, or blows for some other reason and the key is on, the inj and coils will be powered w/o the ECU. Sure, you would not leave they key it on all day like that, but full current would be applied to your injectors at that point, which on mine means 'burns the skin' hot, probably near meltdown. 55W heats up that small amount of metal pretty quickly.

A quick fix to the diyautotune diagram could be to run a single 3A fuse separate from the big fuse block, into the MS right out of the ignition switch... Then between the fuse and the MS, trigger the 12v on the main relay. That way, if the 3A blows or is removed, the main relay can't come on. If you do this, just watch for flyback since that is your main ECU power line. Not saying this is a great idea, just something quick I thought of before I was corrected on the fuel pump driver. Better to just wire the fuel pump relay output pin to your main relay, just beware of current limits, it is only good for 1A.

[Tired2]

The relay driving transistors are a NPN type. No base to emitter current means no collector to emitter conduction. That means the relay coil does not get grounded. Relay coils have 12v supplied and MS ground switches the coil when the uP pin goes high and drives the NPN's base.
Here is how to keep from having problems. http://www.msextra.com/doc/general/ms2external.html

Thanks, this is the part I was missing. I assumed it was a PNP like the injector drivers. Just because it switches the low side does not mean it has to be P-Type, which is something I had wrong in my head and need to research more.

Symtechlabs, I agree the best way is to go through the fuel pump relay, or rather, use its output to switch on the main relay. That way, the MS ECU has to actively power up the coils and injectors. Thanks for your help and resources.

[SymTech Laboratories]

Assuming you are referring to the DIY auto tune diagram, if the 3A fuse is pulled, or blows for some other reason and the key is on, the inj and coils will be powered w/o the ECU. Sure, you would not leave they key it on all day like that, but full current would be applied to your injectors at that point, which on mine means 'burns the skin' hot, probably near meltdown. 55W heats up that small amount of metal pretty quickly.

We were referring to the diagram Mustangous posted. Appropriately sized fuses should blow if low-Z injectors are held open.

Thanks, this is the part I was missing. I assumed it was a PNP like the injector drivers. Just because it switches the low side does not mean it has to be P-Type, which is something I had wrong in my head and need to research more.

The injector drivers don't use PNP transistors, they use N-channel MOSFET's. All outputs in a MegaSquirt ECU use N-channel MOSFET's or NPN transistors. In general, N-channel MOSFET's and NPN transistors are used for low-side switching. P-channel MOSFET's and PNP transistors are typically used for high-side switching, but there's nothing like that in a MegaSquirt ECU.

[Tired2]

We can probably end this conversation now, but I'm still a bit curious why the injectors ground out when power is lost to the ECU, but the fuel pump does not.

As for the fuses blowing on lowZ, I have mine fused at 5A, but with 2.9ohms and 14v, I'm at 4.82A. Maybe I should put in 4A fuses instead, but I'm just going to fix the wiring instead.

[DaveEFI]

We can probably end this conversation now, but I'm still a bit curious why the injectors ground out when power is lost to the ECU, but the fuel pump does not.

As for the fuses blowing on lowZ, I have mine fused at 5A, but with 2.9ohms and 14v, I'm at 4.82A. Maybe I should put in 4A fuses instead, but I'm just going to fix the wiring instead.

I've just checked a brand new MS2 V3 I have on the bench. Powered down, the injector outputs are effectively open circuit to ground. So I'd guess you need to double check your wiring.

[Tired2]

We can probably end this conversation now, but I'm still a bit curious why the injectors ground out when power is lost to the ECU, but the fuel pump does not.

As for the fuses blowing on lowZ, I have mine fused at 5A, but with 2.9ohms and 14v, I'm at 4.82A. Maybe I should put in 4A fuses instead, but I'm just going to fix the wiring instead.

I've just checked a brand new MS2 V3 I have on the bench. Powered down, the injector outputs are effectively open circuit to ground. So I'd guess you need to double check your wiring.

Interesting. I guess I'll have a look at that again tonight with a meter. Thanks. The car runs, so it can't be that big of a problem.

[ashford]

We can probably end this conversation now, but I'm still a bit curious why the injectors ground out when power is lost to the ECU, but the fuel pump does not.

As for the fuses blowing on lowZ, I have mine fused at 5A, but with 2.9ohms and 14v, I'm at 4.82A. Maybe I should put in 4A fuses instead, but I'm just going to fix the wiring instead.

the mosfet controller u4 is behind a diode with a capacitor. when the processor looses power it turns on the mosfet until the capacitor is discharged(c13,c14).
i currently hvae my fans controlled by the injector circuits and they run from 2-10 seconds after the key is turned off