Basic FI requirements?

[robert dingli]

Clint Sharp asked about basic efi requirements,

>  I am going to build my own FI system and I have worked up a list
> of sensors/inputs I think I need. The system will control four injectors
> and two coils (a four cylinder CVH lump) with mapped ignition and 
> possibly sequential injection. Can anyone tell me if I missed anything, 
> or am being hopelessly optimistic here. The sensors I think I need are;
> 1. Crank sensor for RPM and position sensing.
> 2. Cam sensor for ignition and injector timing.
> 3. Airflow.
> 4. Water temp sensor for cold start enrichment.
> Could I get away with using the cam sensor alone for RPM and timing?
> What type of airflow sensor is best, i.e. can I use a throttle position 
> pot and get good results or is a 'proper' flow sensor neccessary? Would 
> retarding the ignition until the engine is hot be worthwile? I would 
> like to use a 68hc11 but am open to suggestions if you think this chip 
> isn't up to it (please no 'my controller is better than yours')
> Thanks for any help/suggestions in advance.

You can easily do away with the cam sensor and simply use a crank sensor
for rpm and position.  You will be firing the plugs once per revolution
anyway and can simply fire the injectors once per revolution as well.
Alternatively, you could use just a cam sensor and get 720 deg information.
You can infer air flow from a throttle position pot, MAP sensor or MAF
sensor depending on your application.  The use of throttle position assumes
a constant upstream pressure and thus isn't useful for turbo applications.
The airflow per cycle (and hence fuel flow) as a function of MAP is near 
linear for any particular rpm and is easy to determine empirically. A
calibrated MAF sensor is also easy to integrate.

Air temperature would be useful for MAP/throttle position/moving vane air
flow based systems.

I don't understand why you would want to retard the ignition until the
engine was hot.  Some systems retard the ignition when the inlet air temp
gets too hot while others advance the idle timing to increase torque
after a cold start.  You can worry about these subtle corrections after you
have the system running.  For refernce, get hold of a copy of Bosch's
little red Automotive Electronics handbook which details the early Bosch
efi and ignition systems.

The HC11 will have plenty of power for an initial diy-efi and is extremely
easy to get going.

Robert
-- 
    Robert Dingli   r.dingli at ee.mu.oz.au
Power and Control Systems    (+613) 9344 7966
Thermodynamics Research Labs (+613) 9344 7712
     University of Melbourne, AUSTRALIA 
**  he who dies with the most toys, wins  **