Wow! Scott.

That Treatise is a HUGE step in helping me understand our trusty steeds
engine operation.

Thanks for posting!

John

On 11/17/2013 12:32 AM, Scott Daniel wrote:
> hi John....
> what is 'injection discharge' ??
> got me there.
>
> let's try this ....
> air is being drawn through the intake manifold and past the open intake
> valve while that cylinder's piston is going down, drawing in the air (
> which is 'pushed' by atmospheric pressure , as you say ) ..
>
> IF it was a timed sequential egine ...the injector would squirt right at
> the intake valve area ...and during the intake phase . Subaru's are
> really, really neat that way. Each injector is 'twin'd'
> .............that is there are two separate sprays coming out of the
> injector together..each stream of fuel aimed right at it's nearby (
> about an inch or so ) small intake valve ( 4 valves per cyldiner , 2
> intake, 2 exhuast ).
> And that all makes perfect and logical sense.
> For the ecu to do that , it has to know where the crankshaft and pistons
> are , which it knows by there being a camshaft and crankshaft positon
> sensor on each of those .
> There's no distributor ....the timing can not be adjusted ..the ecu
> knows completely what's going on, and fires the spark plugs and
> injectors at exactly the right time.  Ignition advance is taken care of
> inside the ECU, completely electronicaly. ( it's also Knock Sensor
> equipped ignitIon . )
>
> on a waterboxer..compared to that , it's really crude.
> The ECU know the engine is turning from seeing the igntion pulses from
> the Hall Sender in the distributor.
> It also knows what the rpm is.
> It does not have any idea what cylinder is being fired or where say
> Cylinder 1 is in the 4 Stoke Cycle.
>
> inputs are ........let's see..
> rpm,
> coolant temp,
> intake air temp,
> air flow meter flapper door and sweeper position on that circuit under
> the cover on the AFM.
>
> ( I don't know if the ECU can sense 'rate of change of throttle
> position'.  I  suspect not on Difijet and Digifant.
>   One some systems ....say early volvo EFI ...there's a a fairly
> sophisticate throttle position switch ( and no AFM ) . The Ecu can see
> throttle position, and also 'rate of change' of throttle position, and
> it uses that info to richen up mixture when the throttle is opened more
> ..exacty analongous to the Accelerator Pump Jet in a carb. ) ( further
> below I'll say what waterboxer EFI uses for an 'accelerator pump jet )
>
> Throttle wise...wbxr ecu's know if the throttle is closed,  or if it's
> at WOT ...and if it's not at either of those extremes.
> Those are the imputs that come to mind right now.
> oh.....here's another one ..'Start Signal' ..the ecu knows when the
> engine is being cranked to start ..to put in extra fuel I imagine.
> (earlier systems had a Cold Start Injector , pre Digijet and digifant
> ..thankfully our waterboxers don't use one )
>
> and oxygen sensor of course...that comes into play after a short period
> of running.  It fine tunes the mixture.  They'll run quite well without
> an 02 input, but having one is better of course.
>
> with that information ....
> the ecu figures out how long to hold the injectors open.
> if the fuel pressure is right ...the right amount of fuel will be injected.
> The ecu has no idea what the fuel pressure is.
> if the fuel pressure is low say ..........for a given amount of injector
> open time...less fuel will be injected.
> The ecu will not even know it, except maybe slightly from the 02 sensor.
> There won't be any codes set or anything like that of course.
> The ecu will just 'try' to do what it can with what it has to work
> with.  Fuel pressure is regulated by the fuel pressure regulator of
> course...a purely mechanical device.
>
> OK ..the 'enrichment when opening the throttle' ....the fuel pressure
> regulator has a vaccum line on it, connected to intake manifold vacuum.
> It's built so less intake manifold pressure equals higher fuel
> pressure.  When the throttle is opened ..intake manfiold pressure drops
> .....raising the fuel pressure as controled by the fuel pressure regulator.
>    if the injectors are held open the same amount of time...more
> pressure means more fuel molecules get injected, thus richening the
> mixture for acceleration. Pretty clever, and fairly crude, but it works
> well.
>
> Ignitio...base timing is set by the rotational position of the
> distributor in the engine block.
> on 1.9's advance is control by centrifugal weights in the distributor (
> how many people or engine techs even know anymore that felt pad under
> the rotor is for a drop or two of oil to lube the centifugal mechanism
> ??? not many I suspect ! )
> Ignition timing is also controlled by the vacuum capsule on the side of
> the distributor.
>
> on 2'1's igntion timing is  entirely electronically controlled. I'm
> trying to think of how it could be load sensitive ...and can't think of
> how it would know that...seems it's only pegged to rpm.  I'll have to
> think about that more.
>
> as for fuel pooling in the intake manifold or anything like that ..
> I just have never seen any concern about that ..........other than a
> sequential system would give more power , possibly better driveability
> and better fuel economy.
>
> I must live in a different world than some people..
> bad 02's don't ruin cats that I've seen ( though to be fair, I am not
> dealing with vanagons that get smog checks ) ...
> intake valves don't get carboned up ..
> etc.
>
> Oh ..i get it. By 'discharge' you might mean squirting of fuel by the
> injectors.
> They're all fired like one big one..
> and it's not really timed, even though injection events are triggered by
> ignition pulses.
> It's kind of imprecise and was 'good enough' for the era.
>
> Just move up to a distributorless, knock sensor, 4 valves per cylinder,
> sequential injection engine ...
> the common subaru conversion. They just rip.
>   What's not to like ? !
> more power, with a  fat power band, better throttle repsonse, better
> fuel economy , and an extra thousand rpm to play with ...
> and ..they use an Air Mass Meter .. ( and some later ones don't even use
> one of those )
>
> if anyone finds this interesting...here is why an Air Mass Meter is a
> huge advance over an Air Flow Meter.
> An AFM has mechanical contacts in it ..those wear. AFM's run 'uneven'
> after a while.
> The flapper door is anther obstruction in the air intake path . A choke
> point.
>
> An Air Mass Meter ....no moving parts. No electrical contacts other than
> the plug on the side of it.
> The way it works is a small current flows through nearly invisible wires
> right in the middle of the air flowing through it.
> The ECU sees changes in resistance in those wires by how much air is
> flowing over the tiny wires.
>
> And get this ....both barometric pressure
> and humidity affect what the ECU sees for air flow ! It can't make up
> for altitude and less air to work with of course...
> but air temp, barometric pressure, and humidity all affect what the ECU
> sees air-wise.
>
>    About all that ever happens to them is junk or dirt gets on the fine
> wires . I have to clean my turbo Volvo  air mass meter wires every once
> in a great while. You can buy air mass meter spray cleaner at a FLAPS.
> I never have to clean Subaru ones.
>
> and then after that ....this 2002 Forester 2.5 I'm almost finish with,
> doesn't even have an air mass meter, just a pressure sensor called a MAP
> sensor ..bolted on the intake manifold. Between coolant temp, throttle
> position and map sensor inputs, the ecu knows what to do.
> And they are really reliable too.
> Seriously ... a well set up subaru engine in a vanagon holds that 'tune'
> very, very well.
> Waterboxers somehow seem to loose it after a while, needing a little
> tweaking or adjusting.
> Waterboxers by the way ..
> in my experience .....the traditional tune up parts ..the ignition stuff
> ...in my world that stuff doesn't even wear , or barely barely. Sure
> eventually those parts wear and need replacing ...and very often cap,
> rotor, plug wires and spark plugs are 'not what's wrong' on a waterboxer
> engine.  I have boxes of good Bosch distributor caps with tons of life
> left in them. Just barely a wear item.  Waterboxers don't use up spark
> plugs very much in my experience either.
>   it's the fuel injection that gets off.
> I do recommend a good fuel treatment and injector cleaner once in a
> while.  I really like SeaFoam.  I would never run a gas vanagon for
> years on end without treating the fuel once in a while.
>
> I hope people can read fast !  lol.
>
> what fun aye !?
> Scott
>
>
> On 11/16/2013 9:42 PM, JRodgers wrote:
>> Ok, sort of a question here. Given how the injectors fire - all four at
>> once - it appears that a "vapor cloud" of air/fuel is provided in the
>> intakes and by way of the rpm and valve timing that cloud is pushed ( I
>> think in terms of atmospheric pressure pushing  rather than a vacuum
>> sucking - but either way - the cloud goes into the cylinder)  into the
>> cylinder  at just the right time and in just the right amount to be
>> ignited at just the right moment. Consequently - individual injection
>> discharge is not needed on the WBX? Do I have that right?? Is that
>> basically the big picture?? Or is the ECU timing the period of the
>> injector pulse to control the amount of fuel for the amount of air
>> through the AFM?? Thus varying the density of the air/fuel vapor cloud
>> in the intake at the cylinder head??
>>
>>
>> John
>>
>> On 11/16/2013 9:00 PM, Scott Daniel wrote:
>>> a few more thoughts..
>>> OK...the injectors fire when there is an ignition pulse , all 4 of them.
>>> So ....for the one cylinder that happens to be just before TDC with the
>>> spark plug firing ..
>>> that cylinder's  injection pulse is actually late for that cylinder.
>>>
>>> the other 3 cylinders .....the injector squirt will be at some other
>>> phase of the 4 stroke cycle.
>>> It works out that things are moving fast enough ..( I read this years
>>> ago in some paper discribing the system )
>>> that injecting into the intake manifold happens continously in
>>> pulses...and it all works out.
>>> and they are not actually timed to intake valve being open say ..
>>> or perhaps one cylinder is . .
>>> while the other injector pulses happen in the intake runners at various
>>> 'not intake valve opening' times.
>>>
>>> That's a more elaborate way of saying what I meant when I wrote that
>>> injection events do not occur in a 'timed to engine position' way.
>>>
>>> Scott
>>>
>>>
>>> On 11/16/2013 5:28 PM, JRodgers wrote:
>>>> Wow!
>>>>
>>>> Thanks Mark, for even more illumination on how things work in our
>>>> mechanical beasts!
>>>>
>>>> This is all great stuff for those of us that don't know!
>>>>
>>>> John
>>>>
>>>> On 11/16/2013 4:24 PM, mark drillock wrote:
>>>>> The injectors do fire in time with the engine position. All 4
>>>>> injectors
>>>>> fire once every hall pulse which happens every 180 degrees of
>>>>> crankshaft
>>>>> rotation, so twice for every engine revolution. The ignition spark
>>>>> is by
>>>>> definition according to engine position and the fuel injectors fire
>>>>> based on the same triggering event that the ignition uses. Of
>>>>> course the
>>>>> ECU adjusts the ignition point to optimize it. The ECU also cuts
>>>>> off the
>>>>> injection pulses when conditions dictate, such as going down hill with
>>>>> your foot off the gas, assuming your throttle position switch is
>>>>> working.
>>>>>
>>>>> Mark
>>>>>
>>>>> Scott Daniel wrote:
>>>>>> minor correction ...waterboxer injectors don't turn on 'every
>>>>>> revolution' ..
>>>>>> They are triggered continously in pulses...or in 'injector on
>>>>>> time, in
>>>>>> milliseconds of duration.'
>>>>>>
>>>>>>   - as one big 4 part injector too btw.  Called batch fire.
>>>>>> Not sequential, not timed to engine or piston position.
>>>>>> Somewhat crude.
>>>>>>
>>>>>>
>>>>> .
>>>>>
>>>>
>>>
>>
>