Questions about our design

[Dale Ulan]

> 1. Since the car is dual exhaust, is there ANY advantage to using dual
>    oxygen sensors? (If we were to use two, we would just alternate
>    reading each sensor, as opposed to reading each sensor every cycle
>    and taking an average).

Not really. Only for stringent emission control. For this, you normally
have two integrators and two block-learns, etc. etc., one for each
side.

> 2. Timing control. Have other DIY implemented this in a fuel control
>    and then release the energy into the coil after a certain delay.
>    This is an oversimplistic view of how it works, but is the basics
>    of it).

I did timing control.... I just used a stock GM HEI coil amp and driver.
It also has a hardware bypass mode built in. After the engine is
running smoothly, you feed pulses to the module and flip the bypass
line high. At this point the computer takes over timing.

> 4. How heavily can we depend on the oxygen sensor? Originally we were
>    planning to use the oxygen sensor as our main source in determining
>    the fuel needs (along with references to a MAF and MAP sensor), but
>    it seems this may not be such a great idea. Any comments?

O2 is a very slow sensor, relative to airflow. It also measures the
state of things after the burn, when you really need a feed-forward
compensation, not feed-back. Feedback is used to fine tuning the
rest of the system. In fact, the rest of the system should be tuned
properly first, then turn the feedback on. I've been working on my
system... first by simulation... and with feedback, many other tuning
problems can be hidden... or made worse... by the presence of feedback.

> 5. Inlet air temperature: Do we need one, or will the combination of
>    oxygen sensor and MAF sensor be enough to take care of air temp
>    differences? (The underlying idea we are trying to achieve is
>    simplicity, yet cutting edge).

MAF takes care of air temperature's effect on density. It may be
useful to know air temp for acceleration enrichment and for feed-
forward compensation of the MAF sensor's response times.
> 
> 6. All along we have been assuming that a MAF sensor would be easier
>    to use as opposed to speed density. Before we totally commit
>    ourselves to MAF, does anybody have any convincing arguments as
>    to why we should consider speed density?

Speed density is cheaper but more of a pain to set up properly.
On the other hand, you need to carefully consider the MAF sensor
filtering system because airflow pulsates much more strongly
than MAP.
Theoretically, speed-density is ideal for MP injection (batch or
sequential), and MAF for TBI, but compensation can be made for
either.
> 
> 7. We are gravitating towards either using the 68HC11 or 68HC16 as the
>    microcontroller for our system. I know this might seem to processor
>    timing, and possibly a knock sensor. And as stated, the output will
>    be a batch injection system).
...
I like the 68332, but.... the 68HC11 can be made to run just fine
for this application. You may run into problems if you try to filter
the MAF signal digitally with the HC11... processing power may be
maxed out, but I haven't tried it. I found I ran out of timers on
the HC11 too easily, but batch injection only requires one or two
timer outputs. One for spark, too.

I may try a 45-degree event-based averaging system this week on the
HC11, and see if it drowns out the processor. This system samples
the MAF system quite often, and comes up with a phase-independant
MAF value.

> 8. Does a home brew system need an IAC, or is this really used for
>    stringent emission control? (As I said, we want SIMPLE!).

That's how I do fast idle. Normally, I just open the IAC to a position
and wind it down as the engine warms up. This is rough but works fine.
It's easier than having to warm up the car with your foot on the pedal
until it's hot. Feedback control isn't really necessary, but an upper
idle speed limit is a good idea. If the engine is idling more than 2000
rpm, close the IAC a bit until it's below 1800 or so.
Whether you use it or not... it's your call. I would, though.

-Dale