ecu voltage problem

[S. Lastuka]

It is a truly bizarre glitch because the engine runs fine with our own 6V
AC/DC Radio Shack power supply and the same chip ran fine in the other
engine we have which is the same model but was mounted on a test stand.
This indicates the code is capable of running the engine.  The motorola
chip actually generates the pulse and sends it to injector drivers
(National LM1949) which then open up the injectors.  The weird thing is
that the input pulse to the drivers (coming from the motorola MCU) is the
exact same length as the pulse from a crank sensor which happens to be 1
ms.  The pulse from the crank sensor feeds into the MCU for RPM
calculation and seems to work just fine regardless of power supply.  
Sean
  

On Wed, 30 Apr 1997, Tom Cloud wrote:

> I would investigate other things than the PS.  Your symptom
> zounds like a glitch somewhere's else.  Not knowing your setup
> nor your code puts me at a disadvantage, but I can't
> see why the power supply would be good enough to allow the
> confuzer to put out a pulse synchronized with the tach but
> not good enough to allow it to adjust the width of said pulse ???
> Still go back to ground loop, but how can that cause a fixed
> pulse ??  Does the confuzer generate the pulse or does it
> just load an external (or internal) counter with the pulse
> width ??
> 
> >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>
> >> 
> >
> >
> >
> 
> Tom Cloud <cloud at peaches.ph.utexas.edu>
>