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Djet injector batch fire
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Intrinsic
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PostPosted: Mon Aug 13, 2018 5:52 am    Post subject: Djet injector batch fire Reply with quote

In another thread, Ray pointed out the pattern for Djet trigger point initiated batch firing of the FI injectors is diagonal, which I had not realized.

What is the sequence for the firing of the injector batches, as determined by the trigger points; relative to the individual cylinder ignition sparks as dispatched from the upper section of the distributor?

Thanks, this will allow me to study and potentially remap my MS injection timing.
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Bobnotch
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PostPosted: Mon Aug 13, 2018 12:11 pm    Post subject: Re: Djet injector batch fire Reply with quote

I believe they fire in batches of 1 and 4 and 2 and 3 (following the spark firing. Granted 2 cylinders will be wet, due to them not being ready to fire at the time of injection at idle.
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KTPhil Premium Member
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PostPosted: Mon Aug 13, 2018 1:01 pm    Post subject: Re: Djet injector batch fire Reply with quote

Depends on the year... later D-jet models changed the timing.
I know they've been posted here, but I can't find them at the moment.
(EDIT: they were hosted on Russ's site, and are gone now. Maybe someone has a scan from the Elfrink/Bosch manuals that show this?)

I have read that L-Jet fires all four at once, and twice for each cycle!
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raygreenwood
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PostPosted: Mon Aug 13, 2018 1:24 pm    Post subject: Re: Djet injector batch fire Reply with quote

KTPhil wrote:
Depends on the year... later D-jet models changed the timing.
I know they've been posted here, but I can't find them at the moment.

I have read that L-Jet fires all four at once, and twice for each cycle!


Yes...for some reason I cannot find my copy of the injection/ignition firing map either. It was in one of the K manuals.

The timing in relation to total crank rotation...was changed in later models...but it just moved the overall injection map some degrees early or late. It did not change the pairs or sequence or injector window in degrees.

I think if memory serves that it made the two nearly ideal injection events...slightly less ideal....and the two "intake valve closed" injection events...a little better. Most probably for better low speed/traffic emissions and better off the line performance.

L-jet gets an impulse every time the coil fires...but I think (going off memory here again)...that the timing circuit in the ECU converts that to two injections per cycle. Do not quote me on that though....I have to consult the books. Ray
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PostPosted: Mon Aug 13, 2018 1:41 pm    Post subject: Re: Djet injector batch fire Reply with quote

Still looking for the two diagrams. They look like the one at the top of page 3 in this document:

https://members.rennlist.com/pbanders/Baumann.pdf

In this version (early?) the injection timing is indicated by the "b" shaded areas. You can see #1 and #4 are injected simultaneously, as are #3 and #2.

Spark ignition is at "c".
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KTPhil Premium Member
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PostPosted: Mon Aug 13, 2018 8:20 pm    Post subject: Re: Djet injector batch fire Reply with quote

Here we go:

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raygreenwood
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PostPosted: Tue Aug 14, 2018 7:27 am    Post subject: Re: Djet injector batch fire Reply with quote

Thank you! I will have to save it in a better place.

Its really odd. On the 1971 and later map....which lists type 3 only......it shows pretty much that all four injectors are firing out of sequence with the valve .....but not quite. Cylinder 1 and 3 even though they START 180° in advance of the intake valve opening point....depending on injection duration at any given time.....they are firing starting very shortly before and are spraying on into the valve opening point.....because both injector channels havd a nearly 180° firing "window" in the trigger points.....which means 360° of crank rotation. So those two are good.

This very short amount of time before...and its really about "time" and not totally about degrees....is the correct way to go.

However 2 and 4 inject starting 360 degrees before......so they finish before the valve begins to open....but very shortly so. Not horrible.

The early map.....is actually better.....or at least will be more uniform in atomization. You have 1 and 3 firing fully during the valve open cycle with possibly some small overlap to a valve that is now closed.....which "could" leave some injection quantity firing against a closed valve.....but at high rpm that will not matter.

Injectors 2 and 4 start firing 50% of their cycle before the valve opens....a d 50% when its open....which is nearly perfect.

Its also not clear whether all type 4 use the early cycle or not. But I have not heard that type 4 had a cycle change.....and because all of the type 4s I have worked with seem to have more even varnish marks in the ports.....when driven a lot in the city as compared to my late model type 3s.....I suspect all of the type 4 are the early pattern.

I would suspect that this pattern change was either to work smoother with the diaphragm style MPS or for lower emissions. Ray
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PostPosted: Tue Aug 14, 2018 8:35 am    Post subject: Re: Djet injector batch fire Reply with quote

I would guess it was all for emissions. By 1970 all R&D efforts at most automakers were aimed at meeting the fast-changing emissions standards.

Two things made this hard for automakers. First, Congress had no real idea of the lead times required for engine development back then. The standard cycle time for a new engine design was 4-5 years, with 3 being the minimum they could run through design, engineering, prototyping, testing, and tooling up. Standards were rehashed in every year, and so there was a mad dash for "band aid" fixes for emissions compliance, there being little time for major advances.

On top of this, the doomsday scenario had all production stopped by 1975 when there were more drastic standards to be imposed. Remember, VW was the first (and for several years, the ONLY) automaker to go into production with EFI, and others tried to make do with CCC (computer controlled carburetors) and the like. No closed-loop EFI, no cats.

The effect of these two situations made the automakers struggle with cheap band aids for the short term, as they threw most of their R&D money into making the large step up for 1975.

Fiddling with injection timing, along with those horrible transmission-controlled spark timing hacks, and a poorly-designed EGR (both mainly for California cars, which at that time had even stricter standards), really reek of band aid fixes for the short term.

Eventually, the timetable was relaxed a little, and then the magic of closed loop EFI and cats made the quantum leap. By then, both the Types 3 and 4 were on the way out, with VW's future being bet on the new water-cooled cars that took their place in the marketplace (sort of!).

This is speculation, but at the time I was following the foot-dragging and fickle Congressional rule-making through the magazines and newspapers of the day, and this was the narrative.
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Intrinsic
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PostPosted: Wed Aug 15, 2018 7:55 am    Post subject: Re: Djet injector batch fire Reply with quote

Thanks to everyone, this is exactly the information that I needed. I will post on how this gets implemented in my MS.
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