ecu voltage problem

[S. Lastuka]

We are using a 7805 1 amp voltage regulator.  We also tried a 1000 uF cap
between 12 volts and ground to no avail.  I am going to run over to the 
ECU and analzye the ground situation since we had the computer
running the engine on a stand but as soon as it was in the car it
crapped out.  Other information: the regulator seems to put out 5 Volts
down to a 7-8 volt input.  The cmos in the 68hc11 will work down to 4 1/2
volts with little problem and can probably drop a bit below that
sometimes. 
Sean
On Wed, 30 Apr 1997, Tom Cloud wrote:

> >I am an FSAE student and we built an EFI computer for the competition.
> >There seems to be a problem running it off the car's power supply, ie the
> >battery.  When it is hooked up to the battery the computer holds pulse
> >widths at around 1 ms per revoltution regardless of throttle position.
> >When we hook it up to the standard voltage regulator used for testing in
> >the lab the car works perfectly with full rpm and throttle range, but
> >can't move because it is attached to an extension cord.  We're using a
> >68hc11 processor.  If anyone has had any weird voltage problems like this
> >any help would be appreciated.  Thank you,
> 
> What kind of regulation circuitry are you using to drop
> the voltage from the automotive 12 volts to your circuit.
> Keep in mind that your regulator needs to be able to deal
> with voltages as low as 8 or 9 volts (cranking) to over
> 15 volts, with voltage spikes maybe as high as several
> hundred.  A resistor/zener or varistor input could squelch
> the spikes (lo-R so you don't lose voltage from current
> drain of circuit).  Put this before your regulator.
> In-line inductors (chokes) work also, but they can
> get big.  Also consider you may have some sort of
> ground loop going on.
> 
> Tom Cloud <cloud at peaches.ph.utexas.edu>
>