Constant Injector Power - Microsquirt

[STH212]

Hey Everyone, our team is using a microsquirt ECU on a WR450 and we keep getting power to the injector as soon as we switch on the relays. The injector and ECU are powered off of the same relay. We measure the voltage across the drain and the input on the injector transistor and got nothing yet the injector is still powered. Is our transistor fried or have we missed something obvious? Any input is appreciated.

[STH212]

Hey Everyone, our team is using a microsquirt ECU on a WR450 and we keep getting power to the injector as soon as we switch on the relays. The injector and ECU are powered off of the same relay. We measure the voltage across the drain and the input on the injector transistor and got nothing yet the injector is still powered. Is our transistor fried or have we missed something obvious? Any input is appreciated.

[Damon Pipenberg]

What do you mean they are powered? Most ECUs switch the low side of the injector, so so the high side of the injector is always at 12V when the power is on. In this case, when the injector is off, you would measure 12V between either terminal of the injector and ground, or 0V between injector terminals.

[STH212]

What I mean is that we're getting 12 volts across injector terminals at all times.

[Ockham]

Just to clarify: when you turn on the ECU/injector relay, the injector opens (static @ 100% duty cycle) without the engine running or any kind of RPM/TPS signal input to the ECU? That's either a wiring mistake (12V & ground at all times), or the ECU thinks the engine is running, and the fuel map is driving the injectors wide open.

Haven't used a MicroSquirt before, so I can't vouch for the off-the-shelf map. Did you assemble the ECU electronics yourself, or was it a prefabricated board? Is the wiring harness custom, or off the shelf?

[wweissin]

Might I suggest that you have a separate relay just for you fuel system (injectors and fuel pump) that is activated by you ECUs fuel pump output. This is a simply safety/redundancy measure we use in all the harness we build.

[PeterK]

wweissin: +1 This is always a good idea.

STH212: Did you confirm that you wired it correctly (especially the switched ground for the injectors). IIRC the harness is labeled very well (assuming you purchased the harness from DIYautotune have the harness). There is also an injector test mode... make sure that isn't enabled.

[Mbirt]

^^^Injector test mode will turn the injector into a tommy gun as soon as you put power to the ECU if you're in it. So I'm with Peter, check to make sure you aren't in injector test mode. If you're not in injector test mode, try it anyway to see if there's any difference in your measurements at the transistor.

[STH212]

UPDATE: So after much time spent with a multimeter we figured out that we had somehow managed to fry the transistor for the injector on the board. We soldered on a new one and now our injector works just as it should. How we managed to ruin a transistor is beyond me. Also, Alex we have a relay for the fuel pump/injector and another for the coil and the ECU driven off of the main relay, but I definitely see the value in your suggestion. I'll pass it on to our EE.

[Drew Price]

Sounds like a Freshy plugged the battery in backwards.

Beware the electrons, they require periodic sacrifices for appeasement....



At least that's what I've learned working in service for the last year....


Drew

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Drew Price:
Sounds like a Freshy plugged the battery in backwards.
Drew </div></BLOCKQUOTE>
Worth elaborating on this...

ECUs like Microsquirt may have reverse polarity protection for the CPU (usually a diode) but that won't protect the output transistors (MOSFETs). These conduct all the time if reverse biased.

If you do not use a relay or similar to provide the 12V supply to the injectors, and you connect the battery backwards, the injectors will just turn on and stay on. This will possibly burn out the loom, transistors or injectors, not to mention the possible dangers of fuel everywhere.

Using a relay under ECU control prevents this. The ECU does not power if the battery is reversed, so the relay is not turned on by the ECU, and the injectors, transistors etc. are saved.

Regards, Ian