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By tigerstyle
#48398
Bit of a weird question here I think, but on my journey into learning FI and Speeduino this is where I got too...

My car is a 1989 Na6 MX5/Miata, I had it running on Wasted Spark + Batch injection successfully. Speeduino is an 0.4.3
I changed it to Sequential Ignition, but it wouldn't run. So following advice on the Facebook page I swapped channels 1+4 and 2+3, and surprise it ran fine. But I am 99.9% sure the wiring to the COPs is correct, I've traced it with a multimeter, and using the test function on Tuner Studio, spark plug 1 fires with channel 1, spark plug 3 fires with channel 2 etc, firing order 1-3-4-2. Verified by a second set of eyes too.
Timing is correct, and checked with a timing light too.

I then made the change to Sequential Injection, and it fired up and ran fine, no need to 'reverse' the channels.

So my question is (eventually...) how do I know if I'm injecting into the open valve (as it should be) or just injecting into the back of the valve (like it does 50% of the time on batch injection) Would it run at all if the sequential injection cycle was opposite to what it should be? Does that make sense?

Because with batch, I understand 50% goes onto the back of the valve, and on the next crank revolution the next injection 50% joins that pool of fuel and goes right into the cylinder. Could it be I have 100% going onto the back of the valve rather than into the cylinder? Can it even run like that?

I'm aware speeduino uses 1-2-3-4 for the ignition cycle, and that has to be matched with 1-3-4-2, but there is no way 1 and 1 can get mixed up, but it only works on sequential if COP1 goes to IGN4 ?

But as it is, both running sequential, it seems to drive fine!
#48400
I think Speeduino times injection by default to finish by 355 degrees whichever stroke. So its trying to inject on to a closed valve. because that is better for atomisation.
you're probably injecting fuel on the compression stroke rather than exhaust stroke, but it doesn't matter much.
your trigger angle may be 360 degrees out.
#48403
There is good explanation in DIY autotune FAQ:

"Sequential injection attempts to only spray fuel while the intake valve is open for the cylinder that is about to fire, which in most cases is only possible at low engine speeds between idle and low speed cruising. Benefits can be seen in emissions, drivability, and fuel economy at these low engine speeds.

Batch injection does not attempt to spray only when the valve is open. It’s a fact that at higher engine speeds you won’t have enough time to spray all fuel while the valve is open, making this somewhat pointless, particularly for a performance oriented application. At these higher engine speeds 99% of sequential systems (exceptions being race only systems with super massive injectors) cannot spray all of the fuel needed while the valve is open anyways, and sprays it both while the valve is opened and closed, very much like a batch system. We’ve dyno tested several cars with using batch fire and sequential injection on the same motor. Peak power was the same without using individual cylinder tuning. However, the sequential fire setup did run a bit more smoothly at idle and at light throttle angles.

There is generally no significant performance difference with a sequential system over a batch system unless you use individual cylinder tuning. There can be minor emissions and fuel economy benefits at very low speeds though. If your tuning budget allows for individual cylinder tuning, it may be possible to pick up 3-4% more power depending on how much cylinder to cylinder variation your engine has."
#48409
tigerstyle wrote: Wed Feb 17, 2021 7:33 pm But, can sequential timing be 'out' do you think?
Yes it can but not like you said. There is little difference in idle speed when injection is in optimal area. Also exhaust emissions drop but it need sophisticated equipment to measure it. And this optimal injection not necessary happens intake valve open but slightly before. There is so called puddling factor in intake runner. In some efi systems it is used for acceleration enrichment: http://www.megamanual.com/ms2/xtau.htm
User avatar
By PSIG
#48411
tigerstyle wrote: Wed Feb 17, 2021 7:22 am… So my question is (eventually...) how do I know if I'm injecting into the open valve (as it should be) or just injecting into the back of the valve (like it does 50% of the time on batch injection) Would it run at all if the sequential injection cycle was opposite to what it should be? Does that make sense?

I'm aware speeduino uses 1-2-3-4 for the ignition cycle, and that has to be matched with 1-3-4-2, but there is no way 1 and 1 can get mixed up, but it only works on sequential if COP1 goes to IGN4 ?
Timing of injection should (at default settings) end at that cylinder's coil firing. You can see this timing relationship in the board LEDs.

Working properly in sequential ignition with COP1 on IGN4 indicates your Trigger Angle is out 360° (1/2 cycle), and changing that should put COP1 on IGN1 with INJ1 ending injection on compression. Yes, the engine will run with injection on any stroke, but better on the best stroke and end-point timing as found by tuning. Many assume "best" is with open-valve, but be aware that is not always true, for different hardware and different goals.

For example, GM sequential were often set to inject only on closed valve (although not just anywhere in the cycle ;)), allowing hot-valve vaporization for better combustion. Systems today often use two injections per-cycle per-cylinder, for the advantages of both methods. However, GM's goals and your goals are likely different, so again, tune it diagnostically in order to find best performance for your hardware and goals.

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