Updated Main Relay theory - Feb14/05

TeGGer=AE wrote:
> I did some checking today as I was driving around. With my ears, I
have
> great difficulty hearing the clicks, so I just reached under the
dash, and
> felt the clicks on the relay as they occurred.
>
> The first click of the Main Relay is DEFINITELY a double-click. The
others
> are single clicks.
>
> The click sequence appears to be this:
> 1) Turn ignition on, both relays close, one very close after the
other. The
> first click is harder than the second
> 2) 2 seconds later the Engine light goes off, and a hard click as the

> second relay pops open and the pump stops
> 3) Start cranking, and a final soft click as the second relay
re-closes and
> the pump restarts.
>
> Therefore, the third click happens BEFORE the engine fires, not
AFTER.
>
> The problem with the relay when there is no third click is that the
engine
> is running on the residual pressure within the fuel rail from the
2-second
> precharge time before the starter was engaged. Once that pressure is
gone,
> the engine stalls.
>
>
> So, a revised sequence:
> ----------------------
> Driver turns key to ON (but not to START):
> ------------
> 1) Ignition switch terminal IG1 sees power. Injectors allowed power
from
> Main Relay term 1 (batt) through term 3
> 2) Power sent thru IG1 to term 5 to a permanent ground at term 2
> 3) First relay is activated as current flows from 5 to 2. ECU
monitors this
> flow at 2, but cannot shut it off. First relay is now powered ALL the
time.
> 4) Closure of first relay will allow activation of second relay (fuel
pump
> relay) from term 1 to term 8
> 5) Before current can actually flow and activate the second relay,
ECU must
> supply ground to term 8
> 6) Grounding 8 causes both first and second relays to close
>
> ***BOTH RELAYS CLOSE AT SAME TIME (DOUBLE-CLICK)***
>
> 7) Current from term 5 is tapped from BEFORE the first relay to flow
> through the closed second relay to ground at the fuel pump from term
7=2E
> This is the fuel pump's ONLY power source, and is available ALL the
time
> from IG1, since it is tapped BEFORE the relays.
> 8) Since engine is not running and ignition has just been turned on,
ECU
> cuts ground to 8 after two seconds allowing just enough time to
> pressurize the injectors. Second relay pops open and fuel pump shuts
off
>
> ***SECOND CLICK***
>
> 9) ECU knows the engine is not running because of the Crank Angle
Sensor in
> the distributor, which it uses to see engine RPM.
>
>
> Driver turns the key to START
> -----------------------------
>
> ***(THIRD CLICK)***
>
> 10) IG1 terminal at the ignition switch remains powered as ignition
switch
> is rotated to START. This is necessary otherwise injectors would lose
power
> 11) ST terminal at ignition switch is now powered, and is allowed to
> activate second relay directly through term 4. ECU holds ground at 8,

> cureent flows from 5 to 7 and pump runs
> 12) There is a redundant activation feed to the second relay during
> cranking, one from 1 to 8, and one from 4 to 8. As starter is
released, it
> stops powering the second relay. The second relay reverts to being
powered
> solely by batt from term 1 to 8, and will remain this way as long as
the
> engine is running.
>
>
>
> --
> TeGGeR=AE
>
> The Unofficial Honda/Acura FAQ
> www.tegger.com/hondafaq/


I took off the plastic dash part thats cover the Main Relay so I can
grab
it. Sometimes my car does not start, I just shake main relay.