Minimum injector time using Megasquirt 2

Spongo · Post by **Spongo** » Wed Apr 09, 2014 8:29 am

Peeps does anyone know what the lowest opening time is supported by the MS2? I have some new injectors that are a tad big but will go low enough at a pinch for the idle, assuming they are OK I should be able to get a little more power out of the engine

Oh and the open time calculator seems to give a consistant result of 1.2ms which seems to be as low as I need to go.

DaveEFI · Post by **DaveEFI** » Wed Apr 09, 2014 11:41 am

I don't think there is a minimum time supported by MS - the time is determined by the injector itself. It should be given in the spec.

I take it since it's MS2 you are using batch fire rather than sequential? If so you may have to go for only one squirt per cycle if the injectors are over large.

Spongo · Post by **Spongo** » Wed Apr 09, 2014 2:55 pm

Yes batchfire it is would one squirt work like that?

stevieturbo · Post by **stevieturbo** » Wed Apr 09, 2014 9:34 pm

1 squirt per cycle is fully sequential and requires an ecu capable of such. ie 8 injector drivers and phase sensor fitted.

Anything other than that is batch fire no matter what way they try and dress it up.

Sometimes ecu hardware does create a minimum PW they can output, but usually the injector is the main limitation

Especially with batch fire and large injectors.

What is the application and what are the injectors ?

Spongo · Post by **Spongo** » Fri Apr 11, 2014 1:03 pm

Injectors are 550cc (thats at 40 PSI) units and its on a chevy 6.3, they will I hope just about go down low enough for a reasonable idle but will be man enough when I start to upgrade

DaveEFI · Post by **DaveEFI** » Fri Apr 11, 2014 1:57 pm

I'm getting confused - surely you can have simultaneous but not sequential? ie, one squirt per cycle? I'm sure I tried that with my SD1 before settling on 2 squirts per cycle (alternating). If the injectors are too large to give two squirts per cycle then simultaneous would be the only option?

stevieturbo · Post by **stevieturbo** » Fri Apr 11, 2014 6:44 pm

DaveEFI wrote:I'm getting confused - surely you can have simultaneous but not sequential? ie, one squirt per cycle? I'm sure I tried that with my SD1 before settling on 2 squirts per cycle (alternating). If the injectors are too large to give two squirts per cycle then simultaneous would be the only option?

The problem is there are too many ecu suppliers etc making up BS names for different modes of injection.

Sequential is 1 squirt per cycle. ie 1 pulse of the injector per intake valve opening.

In my book ANYTHING other than that is batch fire where injectors will fire more than once per intake valve opening, and these firings will in no way be timed relative to that valve opening.

Doesnt matter whether it's 2, 3, 4 etc pulses, there is sequential, and non sequential.
2 types, nothing more.

So Ive no idea what you're calling simultaneous injection ?

Sequential requires a cam sensor, non sequential does not.

Other than the above...

I guess there is a chance a system might be able to fire 1 pulse per cycle, completely un-timed running off a missing tooth crank sensor only. Not really sure what you'd call that though, or even how reliable it might be.

Spongo · Post by **Spongo** » Tue May 06, 2014 2:25 pm

OK its a wasted spark semi sequential system, engine is a 6.3L chevy and its running about 2.8 ms on idle with the 575cc injectors and I have it at about 13 on the AFR guage so it appears all is well. Just waiting for the Guru to come and pass his magic PC over the ECU

Eliot · Post by **Eliot** » Wed May 07, 2014 7:16 am

Spongo wrote:OK its a wasted spark semi sequential system, engine is a 6.3L chevy and its running about 2.8 ms on idle with the 575cc injectors and I have it at about 13 on the AFR guage so it appears all is well. Just waiting for the Guru to come and pass his magic PC over the ECU

I don't recall being MS2 sequential at all. Have you got a cam position sensor - if not, its not sequential.
As steve says its just batch firing. You can select one or two squirts per cycle, alternating or batch - which just means all 8 at once or 4 and 4.
I'm running 63lb (~600cc) injectors on my 5.7 chevy - I think I had to change from two squirts to one squirt per cycle to get a reasonable idle pulsewidth.
If you have a stimulator you should be able to check your idle and max rpm pulsewidths and duty cycles to make sure it all works ok.

You could also turn your fuel pressure down a little to make your injectors look smaller if you need to.

stevieturbo · Post by **stevieturbo** » Wed May 07, 2014 7:48 am

I wouldn't reduce fuel pressure, its needed to maintain a good spray pattern. So lowering it too much can make things worse.

But 600cc should be fine as long as it isn't a crazy camshaft.

But if you had 8 injector outputs and no cam sensor. In theory it could fire the injectors sequentially. But they might never actually be timed correctly. Just fired one at a time in the order you want.

Given a 720 cycle, it would be 50/50 chance as to whether they ended up timed right once running.

Spongo · Post by **Spongo** » Wed May 07, 2014 7:56 am

When I got the ECU Phil said it would be semi sequential, IE 4 outputs same as the wasted spark and fire 2 injectors at a time at least I think so. That made it semi sequential I believe or am I wrong.

Anyway long and short is its running well sort of and will hopefully be much better once Shaun has visited.

DaveEFI · Post by **DaveEFI** » Wed May 07, 2014 8:06 am

Megasquirt with no cam sensor gives the choice of firing all in injectors together or each bank alternately, since it has two drivers and it's usual to split the injectors into two groups. You can also choose the number of times they in inject per engine cycle (within defined parameters) The norm on a standard RV8 would be 2 squirts per cycle and alternating. That's how Lucas did it on the flapper. But if you have over large injectors, you may need to go to one squirt per cycle to stay within the minimum opening time.
The flapper had the injectors grouped as left and right bank. Mine are wired thus:-

I can't swear it is better - but think it gives a slightly smoother idle.

To go to sequential you'd need a modified MS2 with an injector driver per injector and a cam sensor.

stevieturbo · Post by **stevieturbo** » Wed May 07, 2014 8:20 am

I've run 750s on mine with batch fire, only time there was a problem was after fitting a bigger cam.. 600s were fine though.

As long as they are good quality injectors, I don't see a problem with batch fire