MegaSquirt For Dummies......

[TC]

Heads up: "Several People" usually means "a few guys running MS on their 80hp Saabs"

Trust me on this: you prefer true PWM as you step up higher in HP/ci. Your pinto engine is capable of an easy 3-4 hp per cubic inch, and to run injectors that large, *you want control of injector dead time* (PWM).

I can go on more if you don't believe me - this isn't an opinion either.

Oh I believe you, but for right now I'm going to fallow their setup instructions to get the thing running and learn the tuning aspect of this.....and then we'll move up the ladder.........

[dieselgeek]

It still would be a good idea to hear from Matt Cramer. I find it hard to believe the DIY-PNP would NOT support PWM ..... ?? that's almost counter-intuitive to going with a standalone EFI system in the first place.

[TC]

It still would be a good idea to hear from Matt Cramer. I find it hard to believe the DIY-PNP would NOT support PWM ..... ?? that's almost counter-intuitive to going with a standalone EFI system in the first place.

Ya I to would like to know Matt's opinion on this, I mean I'm just new to all this and don't really know why they do it this way.......

[TC]

It still would be a good idea to hear from Matt Cramer. I find it hard to believe the DIY-PNP would NOT support PWM ..... ?? that's almost counter-intuitive to going with a standalone EFI system in the first place.

Was doing some reading and it seems with high impedance injectors you are disabling PWM, or at least that is what it says to do in the MS2/Extra manual..... and just to confirm, I'm running MS2/Extra 3.0.3u Firmware which I believe does support PWM...... The only thing I can think of is they are running the resistors to make the computer think the injectors are "high" impedance injectors, though I'm probably totally wrong about that.....Here's what it says in the manual.....

If you are running high-impedance injectors (greater than 10 Ohms), then set the PWM time to 25.5, to disable the PWM mode. This allows full current to the injectors throughout the pulse width.

For low-impedance injectors (less than 3 Ohms), you need to limit the current to avoid overheating the injectors. To do this, there is a period of time that you apply full battery voltage [peak] current, then switch over to a lower current-averaged [hold] current, i.e. peak and hold. Alternatively, you can add resistors in series with the injectors.

http://www.msextra.com/doc/ms2extra/MS2-Extra_Conversion.htm#injchar

And one other question that I have is I'm sure the car has a narrow band O2 sensor on it form the factory......would you recommend replacing it with a wideband O2 sensor..........or is the narrowband good enough........I'm kind of wondering which is better to use with the auto tuning feature that TunerStudio has..........

[dieselgeek]

TC, on a turbo motor that you plan on "turning up" you *most definitely*want to go with a wideband O2 sensor kit IMO. A narrowband sensor is really just a switch that toggles around 14.5:1 AFR. So you can't use it to tell, for example, that you are running 11.5:1 AFR at WOT under boost. Note that you need a controller for the wideband, so you will want to purchase a kit - something like an LC1, LM2, AEM UEGO, or one of many other units out there. Double check what units are pre-configured in TunerStudio as some systems (like that POS FAST dual channel wideband) are a pain in the ass to set up. All of the popular widebands are supported, but be sure you check with us or in TunerStudio before pulling the trigger on one.

For the injectors, it sounds to me like the DIYPNP doesn't have the right hardware to support PWM, since they seem to be recommending "resistors" to limit current when you use low impedance injectors. It'll work but it's not my favorite approach - in my mind, any standalone EFI system needs to support PWM or some other non-resistor method of current limiting... but it's no a show stopper.

Matt's been quiet lately, he must be busy.

[Bamfster]

On the subject of WBO2 ... wasn't there a thread on here (I searched but can't find it) that showed a DIY WBO2 controller? Seems to me it showed using parts and pieces available at Radioshack ....

[squirrel]

The impedence of the injector determines how much current you have to give it to make it open, and stay open.

High impedence injectors take less current to open, and you can leave that lower current applied while the injector is open.

Low impedence injectors take more current to open, and if you keep applying that high current once it's open, it might overheat the injector (or the injector driver)

PWM is a way to modulate how much power is going to the injectors, by sending a high frequency signal that is on, off, on, off, etc with a varying ratio of on-to-off periods. That's the Pulse Width, and the changes in it is the Modulation. PWM = Pulse Width Modulation. So you would send a higher "on" time during injector opening, and then reduce the "on" time to hold the injector open.

Also there is the flyback thing, which is built into the V3 boards, but not the V2.2 boards, right? The flyback curcuit deals with the extra power required to run the low impedence injectors.

Adding resistors to the drive circuit for low impedence injectors will reduce the current required for the driver circuit, but the injectors will not open as quickly.

A resistor acts like a current limiter, as Ohm's Law suggests.

Beware that I'm a mechanical guy, and I don't really understand electronics or MS like I ought to...I'm just trying to give a little background explanation here about what's going on, as I see it. I could be out in left field, hopefully someone will correct my mistakes, but at least I got a few points out in the open to discuss, so hopefully Alex can better understand what he should do.

[Matt Cramer]

Right, the V2.2 boards don't have the flyback board, V3.0 and later have it standard.

[squirrel]

You mean I got most of that right? dang...

[Bamfster]

You mean I got most of that right? dang...

If you did .... you actually explained so I could understand it ... thx

[TC]

Right, the V2.2 boards don't have the flyback board, V3.0 and later have it standard.

Hey Matt can you explain the reason for the injector resistors and why they use them........ And does the MircoSquirt v2.2M board support PWM??........And at that have a built in flyback circuit??

[TC]

TC, on a turbo motor that you plan on "turning up" you *most definitely*want to go with a wideband O2 sensor kit IMO. A narrowband sensor is really just a switch that toggles around 14.5:1 AFR. So you can't use it to tell, for example, that you are running 11.5:1 AFR at WOT under boost. Note that you need a controller for the wideband, so you will want to purchase a kit - something like an LC1, LM2, AEM UEGO, or one of many other units out there. Double check what units are pre-configured in TunerStudio as some systems (like that POS FAST dual channel wideband) are a pain in the ass to set up. All of the popular widebands are supported, but be sure you check with us or in TunerStudio before pulling the trigger on one.

For the injectors, it sounds to me like the DIYPNP doesn't have the right hardware to support PWM, since they seem to be recommending "resistors" to limit current when you use low impedance injectors. It'll work but it's not my favorite approach - in my mind, any standalone EFI system needs to support PWM or some other non-resistor method of current limiting... but it's no a show stopper.

Matt's been quiet lately, he must be busy.

On the wideband, I already own a LM2, what I was getting at is can I swap the narrow band for a wideband and run the car on the wideband sensor?? Or am I just better off using the narrowband to run the car on and just use my LM2 to tune it with.......

As for PWM I believe that the DIYPNP "does" support it.........Though I think I found out why they use the resistors......

People running a number of very low impedance injectors on V2.2 main boards have reported problems with the flyback circuit failing. Typically, this will happen with 4 or more low-impedance injectors, such as the Holley 85 lb/hr TBI injectors. This can be avoided by using resistors in series with the injectors, and disabling the pulse width modulation (PWM).

Now what I've read states the the Microsquirt V2.2 board will support PWM for low impedance injectors with or with out a flyback board, you just have to input different values in the tuning software.........Though it seems using the flyback circuit on the MicroSquirt V2.2 board can cause it to fail, which I'm taking that's why they went with the resistors, to avoid the problem of the flyback circuit on the V2.2 board failing and not having to use a seperate flyback board...........

[dieselgeek]

Aha! an LM2 is a heluva nice wideband (just bought one myself, but it's in Doc's trunk after loaning it out at drag week).

What I'd do is, if you want to be able to datalog the wideband O2s is use the 0-5v output of the LM2 and feed it into your megasquirt. Then go out and do some driving and tuning.

You don't HAVE to plug it in to the megasquirt, but then it usually requires two people to do the tuning - one to drive and one to tune on the fly. Either way works, I like having datalogs though.

Any ETA on when we'll be installing and testing this badboy? You have passed the test with flying colors so far - dare I say, an A+ ??? you are really backing up the talk this time.

[TC]

Any ETA on when we'll be installing and testing this badboy? You have passed the test with flying colors so far - dare I say, an A+ ??? you are really backing up the talk this time.

I should get the resistors today, then I have to check a couple of pin outs on the car and see if the wires are there, they are for an automatic transmission, but since my car is a manual and won't use those wires, I was thinking that if the wires are there I could use them as the Injector Outs when I go sequential.........

[TheSilverBuick]

If you are tempted to try out the autotune function (at least in n/a mode) you'll want to hook the WBO2 into the MegaSquirt.