Dwell and HEI's

[Sandy]

EFI332/DIY'ers


Well after some simple testing, I have determined one thing for sure, RFI
will trash the test equipment! My simple pulse generator is housed in a
plastic case and it gets pretty scrambled with the coil attached. I have
another one in the garage, and will have to fish it out but here is what I
got going so far -

Using the 4 terminal older style HEI module -

Current limit seems to be set at 5.5-6 amps. If driving it with a digital
signal, it starts to trigger around 2-3 volts, and the timing does not
change as the input voltage is raised beyond the 2-3 volts. Also, no timing
changes were noticed with the digital drive. For the connection to the
inputs W and G, I grounded W and drove pin G. I didn't try the other way
yet. Initial testing was driving a H1 Haloged headlamp bulb, which seemd to
work OK, I then moved to the dual post GM coil, and all havoc broke out
when the pulse generator get a dose of RF from the spark plugs and wires.
It seems to work OK when I could get it running cleanly. It was hard to
tell, but their may be a minimum dwell time, but I'll have to get the other
generator to verify. 

On a spur of the moment, I decided to try one of the driver boards to see
how well that worked compaired to the GM module. One key thing makes the GM
module a potential downer, and that is the CURRENT LIMIT IS NOT CHANGABLE!
The driver board has the current limit set at 8 amps, and with anything
under about 4ms of on time the IGBT didn't warm, as I went over 4ms mark it
started to heat. So 3.4-4ms seems where the coil saturates to the point of
current limit (8amps). The spark became pretty constant when the on period
was greater then 3.5ms, this is a subjective observation however. Just for
the fun, I tried one of the new coils from the group buy, and it work
equally as well.

The HEI module was a touch more sensitive, or seemd to caused more mischief
with the pulse generator then the driver board with the opto-isolator
inputs, but both still would scramble the pulse generator.

One cool thing, I did find that you can use the HEI modules as a nice turn
signal driver, add a 555 and you have a rugged current limited switch ;-)

Sandy