ecu voltage problem

[Sandy]

At 03:28 PM 4/30/97 -0700, you wrote:
>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.

Sounds bad, as 6VDC into a 7805 is not very good, Look at the LM2925, much
better device. Is the battery 6VDC too? If the Power supply is not
requlated, typically the output will be higher then 6VDC, enough for the
7805 to work properly where the battery at 6VDC is marginal. 

Watch out for rated voltage of CPU, as the Temp goes up the voltage
required also goes up. Also the current drive from the LM1949's can be
quite high also causing some odd glitches if the supply is already on the
edge.

If you have a schematic that you could post that would help in finding the
problem too.

The interesting thing, is that 1MS is pretty short to run injectors, I
think the min time event for the faster injectors is closer to 1.5ms. 

A scope will be your best bet in finding the problem, check for clean power
before and after the requlator. Check anything that you can stick a probe on 
;-).

It is not clear if the pulse from the CPU to the lm1949 is OK, Is that the
source of the problem or is it the lm1949?

Sandy

>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