ecu voltage problem

[S. Lastuka]

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,
Sean