Date: Sat, 16 Nov 2013 22:32:59 -0800
Reply-To: Scott Daniel <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel <scottdaniel@TURBOVANS.COM>
Organization: Cosmic Reminders
Subject: Re: Arduino and Vanagons
In-Reply-To: <5288572C.4060906@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
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.
>>>>>
>>>>>
>>>> .
>>>>
>>>
>>
>
