What about MOV's?  Typical transient response time measured in nanoseconds...

   <Marv>  

My expert, who has designed ECUs for other applications, had the following comments that may be of interest:

 

As far as the ECU goes, the diodes should be replaced with

tranzorbs or zeners of about 30 volts.  I don't think a pull down resistor

of 1K as suggested will do anything at all.  It should be roughly 8 times

the injector resistance (assuming the injector hold current is less than 8

times the pull-in current -- typically it's between 4 and 6).  And if you

want a true peak and hold injector driver, then the National LM1949 is the

way to go.

 

The resistor only makes

sense at very high RPMs, probably higher than what the engine can do, so I

consider it optional.  The relay contacts are not the issue.  The issue is

protecting the drive transistor which will fail at voltages lower than what

will cause an arc in the relay (not to mention RF noise).  The other issue

is minimizing the current flow as the magnetic field collapses.

 

As previously mentioned, the ‘correct’ way to drive a high flow rate injector is using a

peak and hold circuit.

 

FWIW;

 

Al G