2Lucky2tha7

iTrader: (3)

After finally updating to the latest ms2extra firmware (3.3.1), on a 3.0 board, I noticed a separate setting for secondary injector values. The car runs and all, so there is no problem there, but I want to fine tune it more. My injector setup is RC Engineering 750's and Bosch 1600's. All injectors are peak and hold. I know the dead times for both and have them set. I have the PWM Time Threshold and PWM Current Limit set for the primaries according to the megasquirt manual - and I don't use resistors. So, my question is, how do I know what values to set for my secondaries? My primaries are set at 15% and 0.9 ms, but the default values for my secondaries is 50% and 1.0 ms for both PWM values. I set "different bank settings" to ON because of not only the injectors being of different manufacturers, but the dead times are quite different - 0.350ms vs 1.000 ms dead time. I've been searching quite a bit, but all I can find refers to setting the primaries - or just setting injectors in general - but I can find no mention of setting these values for secondary injectors that are staged.
Can anyone shed some light on this? Thanks.

Brian

muythaibxr

The only way I can think of to do this is to temporarily make them the primaries and tune like you would with the primaries. The engine probably won't run very well like that even when they are set up right though.

The other thing you could do is get the jbperf P&H driver circuit and wire it in and set the PWM settings on the MS like you are driving high impedance injectors and forget about the settings.

2Lucky2tha7

iTrader: (3)

Thanks Ken. Your right that it may not run good on the 1600's. I also saw when I was searching, a topic I came across about running 1600's as primaries and the common statement was that they are only good from 2.0 ms and up, but not below 2.0 ms because thats where they get finicky. Seeing as I run around 1.3 ms at idle with the 750's, it would run rough indeed! Is there perhaps a common value I could use for the secondaries, say 30% and 1 ms? Wouldn't there be better response time with the more accurate values for peak and hold injectors?
Thanks for the suggestions!

muythaibxr

I don't know of any common values.

The other thing you could do is set up an "experiment" with an injector in a cup, and run test mode at various pulse widths to see when it starts injecting and how low you can go with PWM before it starts affecting the amount of fuel being injected.

Ken

2Lucky2tha7

iTrader: (3)

Thanks for all your suggestions Ken, I'll post up when I find out what works to get the settings

2Lucky2tha7

iTrader: (3)

I'm beginning to rethink all this. I remember reading a long time back that running a low-z setup is indeed better - and this is the route I took with this project years ago. But, is there really a benefit to be gained from running a true low-z injector setup over a high-z setup for Megasquirt specifically? Even in the MS3 documentation, all I can find is a guide to making a high-z setup from low-z injectors.
So, in my case, is it truly worth getting the exact PWM values for my low-z injectors over installing resistors or a peak & hold driver circuit (or external box) like you mentioned, hence making it a high-z setup?

muythaibxr

The peak and hold driver method is better in my opinion that doing the PWM. It basically automatically does what you have to do manually with the PWM.

For the primaries, getting a low dead-time when you have big injectors is a must, since the engine won't run very well if you're fighting with the dead-time.

However, for the secondaries, it's less important. It's mainly important from the standpoint that you want to make sure you're actually spraying fuel when they first engage since you're reducing the primaries at the same time.

With table-based staging you can pretty easily tune around these kinds of issues though in my experience.

Most injectors even when you factor out dead time have an area at low pulse widths where they don't inject fuel in a linear fashion with increasing PW (so say the dead time is .8 ms, then from .8ms PW to 2ms, the amount of fuel being injected doesn't increase linearly with PW). It's important to try to avoid that or account for it when you tune staging.

Ken

2Lucky2tha7

iTrader: (3)

That's interesting, I wasn't aware of that. That would probably explain some problems I've had at idle over the last few years - sometimes it would die for no reason (I couldn't track it down) as well as a fluctuating idle. For some reason, I also mistakenly thought a driver board was a different way of essentially using inline resistors for all the injectors. I really didn't want to make for sluggish injectors by adding resistors, hence why I didn't go that route with this build.
But, now that you mention all this, I looked up the J&B board, and I see there are essentially 3 versions. Are they all essentially the same? After looking around a bit more, i found another and it looks to be essentially the same as the J&B. It's a P&H driver board for Megasquirt from Symtech Labs.
There's also an article I found basically saying what you just said:
http://www.symtechlabs.com/support/k...gasquirt:low_z

And then the Symtech Labs driver board they sell for Megasquirt:
http://www.symtechlabs.com/catalog/p...oard-p-65.html

It seems that your suggestion of a driver board is really the best option. Thanks!

Jobro

iTrader: (2)

Bosch 1600's are roughtly 4.5 Ohms. Each injector driver on the V3 PCB will handle 2 of them wired in parallel, I ran my old setup like that for years.

2Lucky2tha7

iTrader: (3)

Jobro, you are absolutely right - the trouble is that since I haven't been running resistors or a driver board, I either need to get the PWM values spot on or else I get a driver board. It also seems especially true for the latest firmware. It specifies this. I did realize recently that I had been using the general recommended dead time setting for my primaries for a long time, and apparently that same setting applied to my secondaries as well (I'm pretty sure). But even then I was too high. I was at 0.9 ms dead time for the primaries, but now it's at the 0.350 ms it's supposed to be at for these specific injectors. On a side note, I do use table transition for staging and it has always been flawless.
I have to recheck the pwm parameters again at idle, but the trouble is the secondaries. I know the dead time is between 0.99 ms and 1.0 ms, but I don't have values for the pwm current limit and the pwm time threshold, and to find these values will take some work and testing.
Or a driver board.
This is the problem.