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I have an '03 F115 with a high idle, no rattle from IAC at shut down, took it out and activated with YDS stationary test, did not move. Does not get hot (or even wsrm really) when motor is running either. I read an earlier post where rodbolt stated 2 of the 6 wires should be 12v from the ECM, only one of mine is 12v. Motor runs fine in all other respects, am I looking at an ECM with an open circuit to the IAC or a totally dead IAC?
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the ECM controls the ground path.
without the harness diagram in front of me I cant say out of memory where the 12+ comes from. -
the answer is "neither"Originally posted by JonB1436 View Post
if you actually do not have 12V on one of those two red/yellow wires:
You have a "bad connection" or damaged wire.Comment
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There are two red/yellow wires connected to the IAC/ISC valve connector. There should be battery voltage on both of those wires when the key is on. When measured to ground on the engine block.
The ECM does not supply electrical power to the IAC/ISC valve. The ECM grounds the device to operate it. Through the other four wires.
All of this is clearly depicted in your service manual.Comment
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Thanks for the help, the service manual does show all the 12v wires going to a junction plug (near the flywheel), however the manual shows the feed for that comes from the ecm plug. But all the rest are good so I must have a bad wire/connection.Comment
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re read your diagram. the 12V + source does NOT come from the ECU. the ECU simply toggle the ground path to make the stepper motor run CW or CCW.Comment
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The ECM does not feed power to the ISC valve. That comes from the junction plug as you note.Originally posted by JonB1436 View Post
The ECM provides a ground to the valve to make it function.
You may be thinking that the circuit is like your house, where a switch is closed to apply voltage to a device. Say a light bulb. The valve is not wired like this. The valve is wired so that it has voltage any time the key is turned on. The ECM then makes the valve work by connecting the ground lead.
It would be like wiring a light bulb to a battery as depicted in the illustration below. Just the opposite from the way that everything else in the boat is wired. It can mess with peoples mind when they are trouble shooting.
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What is the purpose of using the ground rather than positive to control this valve? Being a boat, is it really a ground or a common connection?Comment
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The boat is the boat and the motor is the motor.Originally posted by pstephens46 View Post
Virtually all boats will switch the power positive side to control a device. When it comes to computerized Yamaha motors most (but not all) stuff is switched on and off via the ground side of the circuit.
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there is still the mystery of why, in the manufacture of the valve,
is it advantageous to have two separate pins for (+)
each of which "internally" splits to supply two coils
rather than one power connector common to all four....Comment
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Just a guess on my part but the valve might need to move in both directions. Power applied in one manner opens the valve. Power applied in a different manner closes the valve.Originally posted by fairdeal View Post
Thank goodness for Google.
https://www.circuitspe******ts.com/stepper-motorLast edited by boscoe99; 08-14-2016, 09:54 AM.Comment
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And that diagram seems to match the Yamaha type.Originally posted by boscoe99 View Post
But my point was that there is no need in the circuit design for two separate power supply wires -
(its the same power, and constantly supplied - as has been explained ad nauseum)
It must simply be that in this micro-constructed valve,
its "not worth the trouble" to connect the two power leads within the valve body itself -
and then require only one connector pin for power.Comment
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I think I see your point.Originally posted by fairdeal View Post
Might just come down to design philosophy. The shift position sensor has two separate 5 volts inputs provided to it from the ECM. One for each of the two sensors. I guess they could have run just one wire and then branched to two at or within the device itself.
Same with fuel injectors and coils. Each has its own 12 volt power supply via separate wires from the junction block. Why not use just one wire to power all of the devices at the same time.
I retired from a manufacturing company that was full of engineers. You would not believe the miniscule stuff that the engineers would argue over. Sometimes a fight would damn near break out.
Why does Yamaha use different wire colours for the same circuit? Why does Yamaha use the same wire colours for different circuits? Up is down and down is up. Left is right and right is left. Sometimes. Sometimes not.Comment
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it is called digital logic and MOST electronic digital stuff is wired that way. low lights the light. most of the midrange EFI use a 4 wire single speed stepper motor. the one boscoe pictured is a 6 wire dual speed stepper.why do the have PNP and NPN transistors?why use IGFET and MOSSFET ?mostly it is heat and power consumption that dictates a circuit design.Comment
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Why do some auto car bodies use a positive ground?
Why do some engines turn clockwise and some turn counter clockwise?
Why is the face of a propeller blade facing rearwards?Comment
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