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240 Explain this fuel injection wiring diagram

A

atikovi

Member
Joined
Jun 6, 2005
Location
Suburban Washington DC
There are the fuel injectors at the bottom left getting constant 12V+ battery power from fuse 4, so I assume the ecu puts out a ground signal to the injectors anytime they are to be activated. But....all the injectors are connected together to pin 13 at the control unit. How is that possible? Why would the injectors operate all at the same time? The pistons aren't all at the same position in the cylinders.

 
they're configured for batch fire which was a fairly normal thing at the time. Not sure if it is the same for LH2.0/2 but on LH2.4/3.1 they batch inject once per crank revolution. So two injector openings 360 crank degrees apart per single intake stroke for a cylinder.
 
Half a squirt opposite the intake valve opening, half a squirt closer to it. One of the quirts has a bit more time to evaporate in the intake, and perhaps cool the intake valve too?

It's one of those things that seems to be an issue when you think about it, but in the context of it happening dozens of times per second, the precise timing of the injection really doesn't matter much. What does matter more is that the right amount gets injected.

On the MS3X setup I had on the 16V turbo, I wired it up to do timed per-cylinder injection. Then, messing around with the laptop, I could change how many squirts the engine got per cycle, when those squirts were timed, and even have them all squirt together like the stock ECU does.

And really, back and forth, I really couldn't tell much of a difference. Not at higher RPM's, not at idle (where in theory it should make more of a difference). It just didn't matter. 1 squirt, 2 squirts, batch squirts, individual squirts, timed before the intake opens, timed when it opens, timed opposite. I'm guessing maybe a sensitive tailpipe sniffer might tease out some tiny differences in emissions quality, but in the context of doing a shade-tree tune on a Volvo motor, it didn't matter. Getting that VE table tuned in makes a huge difference, when the squirt/s occur makes practically none.
 
Just two. Once per revolution of the engine, it's two revolutions for the entire 4 stroke cycle.
 
JohnMc said:
It's one of those things that seems to be an issue when you think about it, but in the context of it happening dozens of times per second, the precise timing of the injection really doesn't matter much.
Click to expand...

yep, 46 years and 100s of millions of redblock miles later they are still batch squirt going strong
 
atikovi said:
But it's 4 cylinders. I should have said the injector squirts during each episode of suck squeeze bang blow, no?
Click to expand...

But the injection system doesn't care about 4 cylinders, it's firing all of the injectors at one time, through 1 ground wire.

It's firing them once per revolution, twice per each cylinder's cycle.
 
JohnMc said:
I'm guessing maybe a sensitive tailpipe sniffer might tease out some tiny differences in emissions quality, but in the context of doing a shade-tree tune on a Volvo motor, it didn't matter. Getting that VE table tuned in makes a huge difference, when the squirt/s occur makes practically none.
Click to expand...

There is a old story from the dawn of d-jet. By accident they connect injectors in wrong order, and ended injecting on the closed intake valve. This helped with evaporation of fuel and also reduced HC emissions.
 
D-Jet also did one squirt per rotation, but in two batches. So #1 and #4 got squirted in some probably meaningless relationship to TDC (firing and exhaust strokes), and #2 and #3 also got squirted at the same TDC crank angle.

B30 D-Jet didn't really know it was running a 6 cylinder engine, it still fired 2 batches of injectors, only in groups of 3. But there, the cylinders weren't on the same crank angles, but it didn't matter.
 
I want to say that the later 9xx series ECUs, without the separate start injector, do 1 squirt per engine cycle (2 revs) when running, and 2 squirts per cycle during cranking. I can dig up the pictures if anyone cares.

For comparison, a carburetor and K-Jet both inject fuel continuously. The fuel sits in the intake manifold, with some of it vaporizing, until the intake valve opens. This has worked fine for lots of engines.

Generally, batch injection versus semi-sequential (2x per cycle) versus full sequential (once per cyl), doesn't make much difference unless you're running a cam with big overlap. With big overlap, squirting just as the intake valve opens can result in unburnt fuel going straight thru the cyl and out the exhaust while both valves are overlapped/opened.
 
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