Banking Injectors?
 

So, last weekend, I'm hanging with Joe and Al, and somehow we're talking injectors, and Joe tells me I'm not supposed to bank injectors like I do spark - i.e. not to tie 1&4 as a pair and 2&3 as a pair.

What? I admit, I'm stumped. I don't see how that's supposed to work. If you don't, you're going to get some very weird fueling, where cyl one will see fresher gas than cyl 4?

Someone explain this to me.

I've seen OEMs wire up their injectors every way imaginable on batch fire fours. It doesn't look like there's an absolutely right or wrong way, only what works for your motor.

spark is 1&4 and 2&3
fuel is 1&3 and 2&4

wasted spark.

OMG that makes no sense. Except in ultra short runner cars where fuel could suck around... I don't get it.

Well, find me an ECU with more than 4 outputs, and I'll run sequential.

To me, at two squirts, you're going to have fuel on cyl 1 sitting for 270 degrees and on cyl 3 for 90, totally different levels of evaporation, etc.

Who came up with this?

As I said while standing on my head in the baking desert heat last weekend, Mazda did:

http://img34.picoodle.com/img/img34/...Jm_0324a40.gif

In the higher RPM ranges, is this of any notable consequence (for power/efficiency)?

Intuitively it seems like fuel vapor would remain virtually unchanged through such a brief duration. My intuition usually fucks me though…

At high rpm... I don't know. :-) I've heard all sorts of weird explinations about bank firing, and how it's not too bad, how at low speed it helps. At high RPM, you're right, it doesn't seem there would be a lot of time.

Anyway, with the purchase of my injector driver board, I may very well have to split up my whole wiring harness and run each one independently, tieing them together back inside the case.

That leaves me having to revisit this ridiculous question. Maybe if someone were to bomb all of Mazda's locations, simultaneously, somehow I could ignore this odd news.

Selective ignorance is only a six-pack away.

abe member when you were looking at the hydra?


you know the other option is to shoot fuel in to cool the piston between power strokes.

I think it would take more than 6 for this one. :-)


I dunno about your set up, but with the lowly megasquirt, the fuel doesn't get into the cyl until the valve opens. :-)

I've heard it being used to cool the valves, but it's the exhaust valves that are more of an issue I think. Anyway, care to clarify,I seem to have missed something.

To a certain extent, I think that a lot of this falls into the "it really doesn't matter" category.

I mean, there are a lot of port-injected engines out there that squirt every injector on every pulse, or worse, use continuous injection with variable rail pressure.

Even on a "proper" system with one channel per injector, a lot of the fuel gets sprayed against a closed valve anyway. Heck, for quite a while I had my two injector channels reversed, and after changing them I didn't perceive any notable difference in engine operation.

"Doesn't really matter" is probably the best answer, but it fails to answer the question of "why go out of your way to do it wrong when you could do it right just as easy".

I mean, could they reuse the Y-cable with a 2 cylinder spacing? I don't see why they wouldn't run all cyl the same. Maybe that's why cyl 4 runs hot. :-P

All this tells me they chose it for some reason, some reason I cannot yet fathom

Precisely. It's one of those situations where I have to assume that some smart person at Mazda, who knows more than I do about fuel injection and internal combustion engines, chose to wire the injectors this way for a reason.

A lot of Toyotas are wired the same way as well. For example, here's an '86 22RTE engine:

http://img31.picoodle.com/img/img31/...Em_ec88278.gif

Must be an assembly thing. Whoever put my car together forgot the turbo

This.

Sequential injection is said not to yield any benefit other than low-rpm idle smoothness (possibly emissions too?).

It's muddying the issue, but I often wonder why people don't run injectors big enough (1600cc?) to inject all the fuel while the air is moving. But now we're getting off topic. I got my manifold back, and after a major cleaning it's going back on the car. Maybe I can drive instead of talking about driving for once.

That's done on Formula One engines, which also run ungodly amounts of fuel pressure (like 500 psi or so). For a production car, they just can't justify the expense of such a system.

In the OEM world, we're just starting to see work in this direction via gasoline direct-injection, which is more or less the same technology as common rail Diesel. There are some cars running the system on the road (Alpha and BMW both use it quite a bit, and a few other manufacturers have dabbled, including Mazda with the current-gen Mazdaspeed 3 (DISI) turbo.

...And I'm such a fan of that, too!

Isn't pontiac doing it as well? And how many mega-tons of crack are they smoking not putting that motor in a mazdaspeed miata? One where they leave off the fenders, passanger seat, one headlight and other needless weight....


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So, joe, your answer is pretty obvious: Mazda probably thought it through. Does that mean the general consensus is that I should rewire my injectors to follow that inane scheme?

For what its worth, the MegaManual states the banking of injectors is strictly to help maintain proper pressure in the fuel rail.
--Alex