Elon,
In reverse order; ECUs generally have two separate internal power supplies.
One feeds the "brain and memory" and is on as long as the master switch is
on. The other powers the ECU's output drivers (e.g. fuel injectors, spark
box, relays, etc.) The important thing to remember, is when the
manufacturers are building solid state electronics, it is much easier to
switch a ground (sink power to ground) than to switch the power (provide
amperage). As such, most ECUs require power be delivered to the device (e.g.
injectors) out side of the ECU.
It is common for a standard Bosch 30AMP relay to be used as the "switch" for
the power under control of the ECU. The ECU only needed to switch a few
milliamps verses the full 30 amps. Since the relay will generally have lots
of excess capacity - why not let it switch the fuel pump? After all, the
fuel pump is not needed if the injectors are in the off state (ignition off
that is). With this type of setup, the ECU can be "running" yet have all
solenoids, injectors, spark boxes, etc. in the off state. As for the
question on the RPM sensor, if the ECU is off (or the ECU drivers have been
told to turn off), the ECU will have shut off the relays hence killing the
power to everything including the RMP sensor - no power, no signal,
regardless if the engine is still spinning.
When I get back from the BUB meet on the flats this week, I can send you a
drawing of the electrical system on the bike. It is far more comprehensive
than most, however it will give you a very good idea on how a system works
and what is art of the possible.
John
-----Original Message-----
From: land-speed-bounces+lsrvette=yahoo.com@autox.team.net
[mailto:land-speed-bounces+lsrvette=yahoo.com@autox.team.net] On Behalf Of 3
liter
Sent: Friday, August 31, 2007 4:48 PM
To: land-speed submit
Subject: [Land-speed] No Hands (I disagree)
I like the logic of the idea but would appreciate a few more details. I am
assuming the ECU senses rpm by some kind of hall-effect sensor or ignition
pulse? That works when you want the fuel pump to turn on but what happens
when you want to kill it? If the engine is already running and you kill the
ECU the rpm sensor is still feeding information. Does the ECU shut down all
solenoids as part of its shut-down procedure? Do you need a "normally
closed" relay so when ECU power is lost the relay automatically goes to its
normal state? An EFI pump consumes copious amps. Can the ECU supply it, or
is there a relay in-line? Sorry for so many questions but you can tell a
MFI guy may be merging into the EFI world :-) -Elon
----- Original Message -----
From: ddahlgren@snet.net, August 30, 2007
Fuel pump switch????? Why noy just let the ecu turn it on..No rpm no fuel..
That way 1 switch turns off ign fuel pump and ecu.. Dave
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