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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. |
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