VW Type 1 "Single port" injection

[tmbryhn]

I'm currently working on an EFi kit for aircooled VW Type 1 engines with singleport cylinder heads+intake.
Singleport = one intake port shared by two cylinders on each side.

Hence, I'm going to run one injector feeding two cylinders.

This seem to fall somewhere between "Single point" and "Sequential"/"Batch" injector mode, and there's AFAIK no way to define that one injector will feed two cylinders with respect to correct fuel calculation and injector pulse sequence.

The firing order is 1-4-3-2, where 4+3 = LH cylinder bank ("Injector B"), and 2+1 = RH cylinder bank ("Injector A").

Ideally, the injection pulses should be ABBA throughout one complete cycle starting on cyl#1.
Can this be implemented in software?

Since I'm developing a kit for a certain market, there would probably be multiple engines running this configuration going forward.
I'm willing to have this as a "bounty job" for whoever is interested in coding this feature.

[mck1117]

Run it in batch mode, but with the fuel injector flow rate set to half what it actually is. The fuel injector flow rate parameter is actually "injector flow per cylinder", not "injector flow per injector", but those usually align to be the same thing.

[tmbryhn]

I believe there's one fundamental problem to the above mentioned strategy in this specific scenario:

Because it's a "Siamese port" configuration (each cylinder bank consists of two cylinders and share one port+injector), and due to the fact that the paired cylinders on each bank fire right after one another throughout the cycle, there'll be a mismatch of available fuel locally in the intake manifold runner between the two paired cylinders regardless if you inject four evenly spaced pulses simultaneously (AAAA) throughout the engine cycle, or if you spread four injections across the two injectors in an alternating fashion (ABAB - batch).
This is because the leading cylinder out of the two cylinders in each bank will "swallow" all available fuel in the intake port during its intake stroke, and there'll be only one single injection event (1/4 of the needed fuel) before the trailing cylinder in the bank is ready to be filled (in simultaneous mode).

I think one possible way to work around this problem with the current firmware, would be to run fully sequential with a cam sensor, and connect each of the two injectors to two separate injector driver channels in a way so that the typical ABCD-sequence could be translated into an ABBA from the injectors point of view. That way, both cylinders in each bank should be getting the correct amount of fuel, and the actual flow rate of the injector should be used. However, the effective duty% of the injectors will be twice as high as the duty% reported by the ECU whenever the ECU assumes one injector per cylinder.

I think this will be the solution for now until a specific "Siamese port" feature might be added at some later point.

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[tmbryhn]

We fired up the engine with two injector outputs for the first time yesterday, and my hypothesis as stated above appears to be true; the engine runs like shit with both batch and simultaneous fuel delivery, and the spark plug pairs for each cylinder bank indicates a significant asymmetry in fuel delivery.

We proceeded by wiring four injector outputs to the two injectors in such a manner that we got the ABBA pattern running fully sequential fuel delivery as described in last post, and it did the trick. However, because we're not running a camshaft sensor (yet), we're only hitting the correct injection phase about 50% out of the times we're starting up the engine/resets the ECU. When we miss by 360 crankshaft degrees, the engine runs like shit

[JRD McLAREN]

try read this ...
https://rusefi.com/forum/viewtopic.php?p=46411#p46411

[tmbryhn]

Yeah, similar problem.
We added camshaft sensor some days later after initial startup, and the deal is done.

The only thing missing now is to have siamese port support in software so that we can run the two injectors on one output each in the correct sequence instead of tricking the ecu into thinking it's running four injectors through four outputs. That would also fix the actual injector duty cycle% value.

But for now, it works...

[JRD McLAREN]

Yes .. we have the same injectors configuration ..

4 INJ in ecu configuration ..
but 2 in real life ...

Outputs 1+2 is for 1st injector
Outputs 3+4 is for 2nd injector