MicroSquirt.com read only forum (Jan.15,2018)

Hi guys, I am running a two stroke single cyl with microquirt. Everthing is working great, but I keep having injector issues. I have a fused switched 12v supply from the battery going to one side of the injector, and the injector wire from megasquirt going to the other, I am not running a relay for the injector, just the fuel pump. Here is the problem, motor runs the way I want it too for the first few pulls on the dyno, then after that my motor runs eratic and lean. I tried a new injector and ran good for the first few pulls and then the same thing happened. My motor always runs perfect with new injectors, but only at first. I went threw 3 injectors already. Anbody have any idea what is happeningf here? The duty cycle gauge in mt reads about 30% at wide open throttle, and I am using around 5 ms max. Any help is greatly apreciated.

What are the impedance of the injectors? Remember that Microsquirt can handle 2.4 ohm loads per channel, if you go less then you need to put in a bt of series resistance.

Also, have you run a datalog during this period?

- Bruce

I am runing 1 2.4 ohm injector. I have not dataloged yet. Should I be using a resiter? Thanks for the help.

A 2.4 ohm injector is fine. Lower impedance injectors than ths will not damage anything but the overtemp may shut down the driver.

Yes, you need to datalog and see everything that is going on. Chances are its something else causing the issue.

- Bruce

1 more thing, what should my pwm current limit% and pwm time threshold be set at for a low impedence injector? Maybe my current limit is to high and damaging the injector?

Does microquirt have flyback control already in it?

supertuner wrote:Does microquirt have flyback control already in it?

Yes, the VND5N07 driver used in Microsquirt had the flyback capability - its 70 volts Vclamp rating.

- Bruce

If you are not running PWM ( try 1ms PWM time threshold and 75% ( or less PWM current limit)) if these are not set, i.e. you are suplying full current to your injector, possibly you are over heating your injector. have you measured the resistance of the old injectors? if they have developed an internal short from over heating then the resistance will be less than 2.4 ohms.

The PWM time threshold ( set at 1ms. ) will supply full current to the injector ( 5.625 amps! @ 13.5v ) for 1ms to pull it open, then the PWM current kicks in for the remainder of the pulse width to hold it open at aproximatly whatver reduced current you set the PWM curent limit to. for example, at 75% the hold open current draw will be ~5.625 x .75= 4.21 amps, a setting of 50% would result in ~5.625 x .5= 2.81 amps etc. Thus reducing heating both in the injector and the driver. try to set the PWM current limmit to as low as you can and reliably hold the injector open. 75 is a good starting point, but try it at lower settings, check the Mega manual on this in case i missed something or state it wrong, but it does sound to me like you might be burning up the injectors by not limmiting the current enough.
Joe