Semi-Sequential Injection - Same timing as WasteSpark Ignition?

[stradlater]

Is Semi-Sequential Injector timing/sequencing the same as Wastespark Ignition?

IE, the pairs are the same - cylinder 1 fires on power stroke while cylinder 6 is on exhaust?

[oldcorollas]

semi-sequential?
http://www.m-techautomotive.co.uk/ec...c_glossary.htm

Semi-Sequential Fuel Injection - Semi-Sequential means that 2 or more cylinder's injectors are triggered at the same time, but only 1 time during the engine's cycle. This requires the ECU to be synched with the engine's cycle. Typically injection timing is retarded from the optimum timing point for full sequential by an angle which is equal to 1/2 the angle between 2 cylinders in crankshaft degrees. Semi-sequential allows optimization of injection timing which typically leads to increases in midrange torque and a reduction in fuel consumption for equivalent power compared which Batch fire.

ie, as you said waste spark for injection

the difference between batch fire and semi-seq is that the phasing of the semi-seq can be changed to different parts of the engine cycles..

whereas batch injection is basically semi-seq but with a fixed phasing you can't change

[stradlater]

Yeah, I read that thing from M-tech, and I didn't get the '1/2 the angle between 2 cylinders' thing..

I guess I'll just plug it in and see hey. :-)

so long as I know I wire it the same as waste spark

What does a 1uz use from the factory? It had 2 injectors pair PER SIDE, whcih seemed a bit weird to me?

Would that mean batch?

[Jason Broadhurst]

Usually semi sequential will go in firing order.

Is cylinder firing order 1-8-4-3-6-5-7-2? Therefor if you are runing semi sequential (two injectors per injection output) you will wire injector output to injectors 1 and 8. Injector output 2 will go to 4 and 3. Injector output 3 will go to 6 and 5. Injector output 4 will go to 7 and 2.

This minimises the amount of time fuel has to "pool" in your intake/intake valve. This way, when the second injector is fired the cylinder is almost at an intake stroke.

If you were to run it with the wasted spark timing, the second cylinder would have to wait a full crank rotation and the first cylinder would get ideal injection timing.

[AL510]

Just a quick question regarding sequential injection, do you need bigger injectors for the same power out put as you only have 1 engine rotation for fuel delivery time but with a batch injection setup you would have 2 rotations? or am i looking at it wrong.



"What does a 1uz use from the factory? It had 2 injectors pair PER SIDE, whcih seemed a bit weird to me?"

I think the early series 1uz up to 94 had batch injection then the later ones had sequential.

Cheers, Al.

[wilbo666]

Jason is right, don't wire it like wasted spark!

The below picture shows how Toyota do it from factory

Taken from:
22 EFI#3 Fuel Delivery & Injection Controls.pdf file size 727KB




Cheers
Wilbo

[stradlater]

Fuck, really? I've just wired the bastard to waste spark order...

But it's firing the injectors twice per revolution, which made me think that the waste spark order is fine.

One the first fire it will hit the intake valve of 1 and then on the second fire it will hit the intake valve of 6...

[stradlater]

I mean once per revolution, twice per revolution of the cam.

[oldcorollas]

they only do one injection event per engine cycle? not twice?(duh... re-read twice...)

[AL510]

they only do one injection event per engine cycle? not twice?

Thats what i was asking re the question about injector sizing.

[wilbo666]

Toyota Wired 1UZ as below.

1&7
2&8
4&6
3&5






Below is what would happen if you did wasted spark on a 2 group 4cyl I believe...


Cheers
Wilbo

[oldcorollas]

twice will require not a huge jump in size.. just needs to be big enough to allow another opening/closing event within the 80% duty cycle.. maybe 15-20% larger at a guess (and non guess = latency of 1ms x 2, + 2x pulse width, all within time available per engine cycle at max rpm)

with full sequential, fuel is often fired at closed valve anyway, to cool it and get better atomisation, at part throttle. at full throttle, to only inject fuel when valve is open, at max rpm, takes big injectors!
ie 1 full engine cycle = 17ms-ish at 7000rpm .. assume maybe 200deg worth if injection (when valves are actualyl open) 4.76ms pulse width required... roughly 880cc for a 500ml cylinder.. for NA? = 1800cc for 1 bar boost..

i guess the question is... does "semi-sequential" actually have any "meaning", as opposed to just a fancy way of saying batch injection with more batches? in which case, does it matter which way they are wired?

[oldcorollas]

hmm.. 4 pairs of injectors, with 1 injection event per bank per cycle makes no timing sense at all.
if it was 2 injection events per bank per cycle, then it would make some sense....
or am i missing something?

[stradlater]

yeah, I'm getting the feeling it's just Batch injection with 4 batches.

What I meant to say was, I have 4 injector driver channels.

each one will fire once per revolution. (Crank Revolution)

Ergo, for two engine revolutions, I will have 8 injectors fired, which holds true for waste spark too.

Which is where I got the idea from.

But I might be getting this mixed up.

It may be that I only have FOUR injector firing events per TWO revolutions, meaning that I have to have the injectors batched as above.

I was just assuming that each cylinder would get two lots of fuel, one of which would be wasted. Like waste spark.

[oldcorollas]

well.. unless the ECU is syncing the injection events to a particular timing, it doesn't matter..
and if there is one injection event per batch per engine rev (two per cycle), then it matters even less cos half of the fuel will go to valve cooling/fuel vaporisation anyway....

and then when you are above part throttle and have reasonable duty cycle, it matters even less...

in the interest of keeping everything even, you could wire up to be like waste spark order, but toyota chose to go the route which would reduce wiring (ie, not cross the valley within pairs), but it doesn7t seem to have any timing significance...

in summary, unless they are paired as waste spark order, and fired twice per engine cycle (once per rev) then timing/syncing will not make much difference i can see... since the timing of the injection events will be different for different cylinders.
if it fires once per cycle, then timing is way up to shit and then it won't matter where in the cycle, or what injectors are paired, cos at least half will be way out.

so in the interests of eveness, but not reduced wiring cost, you would wire as waste spark and fire twice. if you can specifically sync with crank position, you might get a slight benefit of having half the fuel going in during intake stroke.. OR so that all the fuel goes against closed valve (for emissions/efficiency).
To get better than that, you would go to proper sequential with 8 drivers, and then experiment with the timing of the injection events, at different revs and throttle positions....

if that makes sense?

edit: the "wasted" fuel is not wasted, and might be better.... since fuel atomisation is the consideration for part throttle efficiency..
if you look at Wilbos first post, bottom sequential diagram, the fuel starts coming in against a closed valve...