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The thing with injectors is that the flow rate isn't all you need to know about them. There is the nozzle spray pattern, but that one is also reasonably easy to understand. Thats determined by the orientation of the injector relative to where it needs to get fuel. Some things are more of a stream, some are a cone, different cone widths, etc.


The more fiddly bit is what Ford at least calls "injector slope". Other mfg may call this something else.

What that ends up translating to is how much fuel is delivered for a given pulse width. Its not quite perfectly linear. The flow rate is measured at 100% duty cycle, injector held wide open and being fed with fuel at some pressure. Injectors should not ever be operating like that. If they are, you need a bigger injector. The flow rate isn't perfectly linear by duty cycle, meaning 1% DC doesn't give you 1% of the marked fuel rate. As you get higher with the duty cycle it gets a lot closer but at low duty cycles things get funky. You have to consider the open and close time of the injector, and at low duty cycle that less than 100% open situation can be a fair portion of the injector pulse width. Thats why some injectors will idle like garbage or have low load drivability problems where others of nominally the same flow rate will run a lot better. Also why generally you don't want injectors that can give grossly more fuel than your engine can ever use.

I have no idea how tunable the Motronic stuff is since my experience is with Ford junk but on Fords you can tune the high slope and low slope, which is basically the low duty cycle and high duty cycle parameters. Getting them right will get the fueling correct from no load to full load, get them wrong and it acts like a badly tuned carb and the fuel trim values end up way off trying to compensate.

1st 5er wrote: Dec 04, 2024 10:26 PM

'sup?

gwb72tii wrote: Dec 05, 2024 7:10 PM

1st 5er wrote: Dec 04, 2024 10:26 PM

'sup?

gadget73 wrote: Dec 05, 2024 9:23 AM The thing with injectors is that the flow rate isn't all you need to know about them. There is the nozzle spray pattern, but that one is also reasonably easy to understand. Thats determined by the orientation of the injector relative to where it needs to get fuel. Some things are more of a stream, some are a cone, different cone widths, etc.


The more fiddly bit is what Ford at least calls "injector slope". Other mfg may call this something else.

[stuff]

more info on "injector slope" from haltech

yeah Ford ECMs don't have the dead time parameter but they do have stuff that effectively covers it. Also handles the rise and fall time for the open and close commands.

but yes if its not correct, the tables end up whacky and it just doesn't run quite right. That last bit they mention at the end is another issue people run into when they think "bigger is better". Massively over-sized injectors do very poorly at extremely low pulse widths. The engine in mine originally specified a 19# injector and it was running in the mid-high 90% duty cycle range at full load. I bumped them to a 24# and its in the mid 80% now. Right on the edge of safety, it should probably be one size larger but I don't drive it in such a way that its really a serious concern so they probably aren't changing any time soon. Friend of mine with a fairly similar engine config that dynos within single digit horsepower to mine has 80# injectors. Apparently that specific one is well behaved at low pulse width, but it seems overkill to me. At full go he's at something like 45% duty cycle.

ok, ok, but is there any down side or reason to not use the newer 4 pintle design from Bosch?

They're fine. Motronic fires injectors in batches, against closed intake valves. Most of the fuel injected pools up until the valve opens, regardless of which injector is used.

A wider dispersion of finer droplets may pool a little less. Don't expect a big difference though.

The later Fords ran those, but using sequential injection. They tend to have slightly smoother idle but its not a major difference. Batch fire I suspect you'd never notice.