Thoughts on replacing 911 SC ECU with Raspberry solution

[AndrewCologne]

Originally Posted by Jonny H

If this project is for your own entertainment then fine. If you are thinking of putting it out there then stop, do some more homework and consider contracting an EE with automotive experience.

(not wanting to piss on your chips, just experience talking)

Thats why Im starting this thread, not to just assemble and doing the code, but gaining from the experience of others and from sharing ideas.

And for sture its not for my own entertainment, if yes then I wouldn't be here asking this in a forum where many with experiences do share their knowledge and could help on for example this idea.

You aren't pissing on my chips at all, but a real gain would be i.E. a statement what could be used so issues like you mentioned above won't harm an adurino set up when using in a car electric environment. I know there are many details I/we should be aware of, so ... as you mention it ... give me some homework ;-) as ... I would apreciate it.

Cheers

[Reanimotion]

If you are primarily interested in messing with the lambda Frequency valve control then there are a couple of choices for ready made hardware

1. MicroSquirt with the FrankenCIS firmware
This gives you as close to automotive capable hardware as you can get on a budget of a few hundred dollars
Owning the hardware gives you permission to modify the MicroSquirt source code to your liking as long as it is only run on genuine MegaSquirt hardware. Our additional code module for CIS is licenced under Apache 2.0 so you can pretty much do as you please with our portion of the code and integrate it into anything else.

2. Speeduino https://speeduino.com/forum/app.php/page/buy
A more DIY project at around half the cost of the Microsquirt, but has the advantage of being Arduino based with fairly mature firmware that runs engines, bringing across the CIS specific code from FrankenCIS shouldn't be too difficult. You could also easily start from scratch with your own implementation

both run similar main power circuitry which I would rate as 'sufficient', protection designs on inputs and outputs varies from absent to marginal between the two.

CDI can be driven by either system with a little circuitry to do the AC signal, or go fuel only control and use CDI+ from Jonny for ignition

I spent most of 2015 designing and prototyping specific custom hardware for FrankenCIS only to abandon the idea as it became obvious there was no commercial value over the currently available products. Those that could afford EFI were converting and those that couldn't were after something really inexpensive. The I like CIS so I'm staying for the fun of it group could be counted in single digits.

[AndrewCologne]

My idea here also was to feed a new DIY ECU with a wideband signal instead of a narrowband one.
Yesterday I received the LC-2 Wideband Controller/Gauge from Innovate, coming with a BOSCH wideband LSU 4.9 O2 sensor.
It works just fine and on the first test run beside the wideband output it also simulates a 0-1v narrowband output which works flawlessly with the original ECU.
This controller provides a ready to use 0-5v signal which can easely be interpreted by an Arduino setup. ... But I will keep a narrowband 0-1v option in this DIY ECU project as well. So no expensive wideband controller and sensor would be needed to make it work but a narrowband "bouncing" signal will be less precise compared to a wideband one.

So I ordered a lot of stuff, like an Arduino Nano, a step down DC converter to keep a safe liniear 12v input, and all other needed electronic parts.
As Im in C programming language I wanted to crack this nut and decided to start this project, as for this less money it could be really worth it.

The signal of the existing VDO 15°c and 35°c temp "switches" shurely will be taken into account as well as the obligatory throttle switch and Microswitch

[Reanimotion]

Originally Posted by AndrewCologne

To me its also difficult to unterstand why Porsche still used a WUR in a lambda and therefore ECU based CIS system where the ECU influences the fuel pressure via the frequency valve directly. The WOT acceleration feature via throttle switch where the ECU enriches the AFR mixture, makes the vacuum in the WUR therefore not needed anymore. Thats why the engineers dropped the vacuum feature and this shows the capabilities of the ECU based AFR mixture.

The WUR is retained on Lambda systems for warmup and base mixture control

make sure you read through Digital WUR plus? ( FrankenCIS )

Good luck and have fun

[AndrewCologne]

Hi Steve,

thanks, and yes, I had a look at many threads here like the Franken CIS ... and in the arduino forums. A lot of useful information which makes this project funny.

Cheers!

[AndrewCologne]

Yesterday I got the Arduino Nano



... and all needed components for a first rudimentary set up.

It works very well!
Providing at 70Hz a PWM signal / duty cycle from 5% to 95%, based on the input voltage (0-5v) from a wideband Sensor/controller like the Innovate LC-2. The wideband voltage here is simulated by an external power supply.
When the sensor voltage goes below 2.5v it leans the mixture by decreasing the duty cycle, same logic in case of voltage rise and therefore needed enrichment.
How fast the duty cycle will be decreased or increased depends on how far away the AFR is from the stoichiometric optimum at 14,7:1, means 2.5v as output in case of the innovate controllers default.



Now, ... adding the support of the CIS switching component inputs like throttle switch, temperature switches, micro switch etc. Here I won't just set the duty cycle to fixed 65% if an acceleration will be recognized but to an optimal AFR target (like 12.5:1) value like for best effective acceleration performance.

Have a nice weekend and cheers from Cologne

[mysocal911]

Originally Posted by AndrewCologne

Yesterday I got the Arduino Nano


... and all needed components for a first rudimentary set up.

It works very well!
Providing at 70Hz a PWM signal / duty cycle from 5% to 95%, based on the input voltage (0-5v) from a wideband Sensor/controller like the Innovate LC-2. The wideband voltage here is simulated by an external power supply.
When the sensor voltage goes below 2.5v it leans the mixture by decreasing the duty cycle, same logic in case of voltage rise and therefore needed enrichment.
How fast the duty cycle will be decreased or increased depends on how far away the AFR is from the stoichiometric optimum at 14,7:1, means 2.5v as output in case of the innovate controllers default.


Now, ... adding the support of the CIS switching component inputs like throttle switch, temperature switches, micro switch etc. Here I won't just set the duty cycle to fixed 65% if an acceleration will be recognized but to an optimal AFR target (like 12.5:1) value like for best effective acceleration performance.

Have a nice weekend and cheers from Cologne

The Nano is a great device for the application. You could easily add the ignition function with as few as 50 lines of C code.

[AndrewCologne]

Hi Dave,

the few lines of C code ain't no problem but the interface to the ignition units and ... the proper timing advance/retard, done by the Ardino setup are the real challenge and ... do enjoy my respect ;-)

[mysocal911]

Originally Posted by AndrewCologne

Hi Dave,

but the interface to the ignition units and ... the proper timing advance/retard, done by the Ardino setup are the real challenge and ... do enjoy my respect ;-)

That's not that difficult, i.e. I've done it! You can easily use the 911SC distributor output as a timing signal. Driving the CDI box is simple too, i.e. easier than for an inductive discharge ignition.
Yes, the Lambda control part is the easier effort.

[AndrewCologne]

Ok, that really sounds very nice!

[mysocal911]

It's a fully functional proof of concept prototype for an inductive discharge ignition system directly driving an ignition coil.
The timing signal input is three pulses per engine revolution. There's a provision to measure load via a vacuum input,
e.g. using a vacuum sensor (upper right) as an input to the AD converter on the Nano.

[mysocal911]

Originally Posted by AndrewCologne

Ok, that really sounds very nice!

Keep up the good effort! You're basically there.

[mysocal911]

Since the Lambda system is a control system with gain and feedback (O2 sensor), system stability is critical.
The 911SC with Lambda typically has about +/- 25-50 RPM variation at idle in closed-loop. If the mixture is too rich
or lean, the system can become unstable resulting in large swings in the idle RPM. If the feedback O2 loop gain
is too great, or the feedback voltage phase is positive, the idle RPM will oscillate greatly.

[Dr J]

I ran an Arduino-controlled DWUR for well over a year with no issues whatsoever related to the Arduino system. You can check it out here: Another digital WUR project Arduino

[AndrewCologne]

@Dave
Yes, and lets see how it behaves in the real worl test later.
As the the original o2 measuring is done via a narrowband sensor, this gives a very less precise "bouncing" voltage output which could cause the oszillating idle.
My routine doesnt increases the duty cycle by a fixed vaue but with a value depending on how far the ideal cycle is away from the expected volatge which equals to a 14.7:1 reading.
So cycle adjustments at round about the 14.7:1 value range are more detailed compared to a suddenly occuring lean out or enrichment condition like acceleration or deacceleration.

@ Dr J
Thanks for your link! Very interesting.

[midnight911]

How are you protecting the Arduino unit from ambient stress like temp change, vibration, etc? Or am I paranoid?

[AndrewCologne]

The DIY ECU will be mounted to the same place where the orig ECU was/is, means under the passenger seat.
The projet in its final stage will be completely soldered on a circuid board.

BUT ... that Arduino project is that funny that I'm thinking about putting it to the center console i.E., cause I made a little control display using a vintage looking green 2x16 LCD display where all the actual details are shown, means here Voltage of the wideband sensor, AFR, duty cycle and the equivalent CO value of the current sensor reading :-)
Or this display could be mounted within the ashtray, so it can be visible on demand, ... lets see.



The vehicles 12v will be connected to Arduino via a specific DC step down element, which provides stable 5v and prevents from voltage peaks as well.

The Arduino forums are full of valuable information and Im very exited about its capabilities.

[mysocal911]

Originally Posted by AndrewCologne

The DIY ECU will be mounted to the same place where the orig ECU was/is, means under the passenger seat.
The projet in its final stage will be completely soldered on a circuid board.

BUT ... that Arduino project is that funny that I'm thinking about putting it to the center console i.E., cause I made a little control display using a vintage looking green 2x16 LCD display where all the actual details are shown, means here Voltage of the wideband sensor, AFR, duty cycle and the equivalent CO value of the current sensor reading :-)
Or this display could be mounted within the ashtray, so it can be visible on demand, ... lets see.



The vehicles 12v will be connected to Arduino via a specific DC step down element, which provides stable 5v and prevents from voltage peaks as well.

The Arduino forums are full of valuable information and Im very exited about its capabilities.

Nice progress!

[AndrewCologne]

Little status update: It works.
Yesterday evening I connected the arduino setup in a simple way to the existing wiring of the original ECU for a fist test. The Plug to the orig ECU was disconnected.

On a first "fixed duty cycle 50%" run, although the Frequency valve was fed by 12v at Herz 70, the mixture was a bit too rich. So I regulated it. Here when regulating the mixture by using the CO-screw I used the CO value on the new display and set it to approx. 0.5-1.0 CO. The idle then was smooth and the working Freq Valve sounded as expected. Even the throttle valve switch worked and pushed the cycle up to 65% as expected when passing the 30% throttle.
So I connected the voltage output from the LC-2 to the arduino and the regulation of the AFR by the varying duty cycle started. Everything was working as expected.

The only thing is, sometimes after driving when the engine changes to idle, independent from the arduino, the LC-2 sensor controller outputs an error and the arduino then interprets the 0v error output from the sensor controller as it should be, means it switches to a fixed 50% duty cycle (like if it was disconnected). When changing from idle to crusing or higher rpms the LC-2 sensor controller starts working again flawlessly.
Here I guess I would have to make a new sensor calibration or check the connections of the LC-2 controller

[Gretz]

Wow. Sounds like things are moving along great. Congrats. I’m very interested in your work.