Why Honda design the main relay this way
#1
Why Honda design the main relay this way
I don't get why Honda design the main relay this way...
Fuel pump relay coil power is from Pin2 (ST switch) and Pin6 (ECU 12V feed) which is controlled by IGN1 (Pin5). Why are there two sources to feed fuel pump coil?
When only IGN1 is on, fuel pump can be controlled by ECU A7,8.
When IGN1 and ST is both on, fuel pump can be controlled by ECU A7,8.
When only ST is on, fuel pump cannot be controlled because it gets power from IGN1.
And I believe when you crank (ST is on), the IGN1 is also on. It is impossible that when ST is on, IGN1 is not on.
Then what is the point of having IGN1 and ST control the fuel pump 12V feed? I don’t get it. Honda…
Fuel pump relay coil power is from Pin2 (ST switch) and Pin6 (ECU 12V feed) which is controlled by IGN1 (Pin5). Why are there two sources to feed fuel pump coil?
When only IGN1 is on, fuel pump can be controlled by ECU A7,8.
When IGN1 and ST is both on, fuel pump can be controlled by ECU A7,8.
When only ST is on, fuel pump cannot be controlled because it gets power from IGN1.
And I believe when you crank (ST is on), the IGN1 is also on. It is impossible that when ST is on, IGN1 is not on.
Then what is the point of having IGN1 and ST control the fuel pump 12V feed? I don’t get it. Honda…
#3
Re: Why Honda design the main relay this way
#4
Re: Why Honda design the main relay this way
Maybe it was for security purposes? Seems like this design would be at least somewhat more difficult to hotwire.....
Maybe Honda adopted some ubiquitous universal relay and that’s just how it was designed....
I mean, how exactly would you have designed it and why?
Maybe Honda adopted some ubiquitous universal relay and that’s just how it was designed....
I mean, how exactly would you have designed it and why?
#7
Re: Why Honda design the main relay this way
Thanks for the explanation. But looking at the relay schematics, how does the relay work as described?
"One relay supplies battery voltage to ECU, power the injector, and power the second relay" => I understand that. Pin 5 and Pin 3 power the coil and Battery Voltage flow from Pin7 to Pin6 which powers ECU and second relay's coil.
"The second relay is energized for 2s when ignition is switched on" => I guess that is controlled by ECU pulling down Pin1 for 2 seconds to allow battery voltage flow from Pin6 thru second relay's coil. That is understandable.
".... and when the engine is running which supplies power to the fuel pump" => When engine is running, ECU pulls down Pin1, current flow from Pin6 to Pin1 to activate the coil. Pin5 supplier power to fuel pump. That makes sense too.
So it is Pin1 (ECUA7,8) is controlling the fuel pump all the time.... Then what the hell is the function of Pin2 from crank signal???
"One relay supplies battery voltage to ECU, power the injector, and power the second relay" => I understand that. Pin 5 and Pin 3 power the coil and Battery Voltage flow from Pin7 to Pin6 which powers ECU and second relay's coil.
"The second relay is energized for 2s when ignition is switched on" => I guess that is controlled by ECU pulling down Pin1 for 2 seconds to allow battery voltage flow from Pin6 thru second relay's coil. That is understandable.
".... and when the engine is running which supplies power to the fuel pump" => When engine is running, ECU pulls down Pin1, current flow from Pin6 to Pin1 to activate the coil. Pin5 supplier power to fuel pump. That makes sense too.
So it is Pin1 (ECUA7,8) is controlling the fuel pump all the time.... Then what the hell is the function of Pin2 from crank signal???
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#8
Honda-Tech Member
Re: Why Honda design the main relay this way
And I believe when you crank (ST is on), the IGN1 is also on. It is impossible that when ST is on, IGN1 is not on.
Then what is the point of having IGN1 and ST control the fuel pump 12V feed? I don’t get it. Honda…
Then what is the point of having IGN1 and ST control the fuel pump 12V feed? I don’t get it. Honda…
And the reason is so you can crank the starter longer than 2 seconds to get the engine started, if needed.
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