Sequential injection / waste spark questions

[driftxsequence]

Hey guys I've had my turbo M20 325ix running for about a year now. Over the course I've put about 6000 miles on it and gradually dialed in the tune. I'm pretty satisfied with the car but wish I could get some of the finer on/off throttle details dialed in.

Reading this here, I'm curious if its my tune that needs more adjustment or if sequential is what I need to do. https://www.diyautotune.com/support/...ch/sequential/

Thinking about it now, I guess the factory used batch fire so there shouldnt be any reason for me to have the on/off throttle dialed in. :(

Additionally if my standard oem ignition system is okay, is there any reason to switch to wasted spark?

[citizen_insane]

The general consensus is that sequential injection doesn't really buy you anything but more complexity. I tend to agree. It sounds like a good idea in theory, but when you realize that you have 10+ injection events per second, it's really chaotic in there and timing the injection with the intake event doesn't mean all that much.

If you're having issues with tip-in and tip-out, try messing with the accel and decel enrichment settings. Not sure which ECU you're using, but with my MS3 I've found I get better response using pedal based rather than MAP based accel enrichment.

[Digitalwave]

I've been told (don't have any direct experience) that sequential makes the most difference at idle when the pulse widths are very small. I don't think you would notice much if any tip in/tip out improvement by switching to sequential.

Can you be more specific with the issues you are having? Posting a link to your MSQ may help too, there's some good tuners on this board that would probably take a look and see if they have any suggestions.

[digger]

unless youre using really big injectors that operate at a low duty cycle approx 25-35% @ maximum hp so you can phase the injector event correctly (i.e. while inlet valve is open and port speed is high ) at all rpm then full sequential wont do much for you at WOT. you should get slightly better fuel economy and it might drive slightly smoother but that's about all and it is only "slightly".

[varg]

Whether or not you need a wasted spark conversion is pretty easy to determine. Do you experience misfires at full boost with good ignition wear parts and properly gapped plugs? If you don't, it's pretty pointless to do the conversion because you won't really gain anything from it. I cruised through your build thread for more info about your sequential injection question, and while you are running pretty radically oversized (600cc/min) injectors which may make it difficult if not impossible to idle well at a reasonably lean AFR, it's unlikely you'd see much of an improvement outside of that and some low rpm part throttle transient areas. And it's a lot of work to do that conversion and time the injection events properly.

The problem with big injectors like that is that in low fuel demand situations the injector pulse widths will often drop below the operating range of the injector (typically 1.5ms and up). If you try to use the injector with such low pulse widths you will see unstable fueling, AFR will sometimes vary even if the pulse width stays consistent, and as a result idle will be unstable and you may experience bucking or random misfires when driving slowly in this part of the VE table. The only solution is often to run the engine very rich, I've seen situations where the car has to be idled at a 12:1 AFR to idle smoothly due to this issue. Batch fire makes the situation worse because the injection timing isn't optimal. If you have your tune otherwise fully dialed in and your idle, low-load performance and fuel economy bother you enough to do something about it, it's going to be more cost effective to get more reasonably sized injectors which will operate in the 2ms range at idle than to do a sequential injection conversion. Honestly, you don't need 600cc/min worth of fuel, you'll start breaking ix parts before you're making the kind of power that warrants that much fuel.

[e30davie]

Wasted spark has the advantage of removing mechanical components, but reality is distributors, caps and rotors generally give very good service. But you can set up wasted spark pretty cheap if you buy the right bits.

TPS based accel enrich made a huge difference to my NA m20 tune. Everyone has their own way of tuning but I log various throttle changes, then i view TPS, TPS dot (change in TPS), AFR, target AFR an acceleration enrichment. when you stab the throttle you can see the AFR go lean and see the accel enrich trying to correct it. Unsure what computer you are running but the megasquirt has 3 or 4 TPS dot enrichment settings, slow change, mid change and fast change. It did not take me too long to get the enrichment dialed in with this method, and small changes made a huge difference to tip in of engine.
This was the main advantage i got from tuning my NA engine, soo much better than stock on throttle changes.

[citizen_insane]

Wasted spark has the advantage of removing mechanical components, but reality is distributors, caps and rotors generally give very good service. But you can set up wasted spark pretty cheap if you buy the right bits.

TPS based accel enrich made a huge difference to my NA m20 tune. Everyone has their own way of tuning but I log various throttle changes, then i view TPS, TPS dot (change in TPS), AFR, target AFR an acceleration enrichment. when you stab the throttle you can see the AFR go lean and see the accel enrich trying to correct it. Unsure what computer you are running but the megasquirt has 3 or 4 TPS dot enrichment settings, slow change, mid change and fast change. It did not take me too long to get the enrichment dialed in with this method, and small changes made a huge difference to tip in of engine.
This was the main advantage i got from tuning my NA engine, soo much better than stock on throttle changes.

This was my experience as well. The main issue I found was that there's still a lot of drive line lash (at least in my car) that makes the car feel like it's stuttering a bit during harsh accel/decel maneuvers. Are you sure what you're feeling is engine hesitation and not drive line movement?

[driftxsequence]

Thanks for the replies guys, it turns out I had the timing set incorrectly at the low load map area so when I would shift the car would stutter as load came back in. I'm good to go now.

I appreciate the input here and it appears sequential is more hassle than its worth, even though every MPG would help on the IX.

And considering the build is a very basic setup theres no need to do anything with the stock coil setup until something fails.

[LowR3V'in]

any write ups on how to tune the accel enrich?

[Jaxx_]

any write ups on how to tune the accel enrich?

https://www.youtube.com/watch?v=HSE3CxaWF-I

this is only time based AE, not EAE or x-tau